texts: Unit analysis for neutralization reaction

texts:
What volume of $\pu{0.500 mol L-1}$ $\ce{HCl}$ (in $\pu{mL}$) is required to neutralize $\pu{2.02 g}$ of solid $\ce{NaOH}$ pellets?

So far I have tried regular unit analysis:

2.02 g NaOH * 1mol NaOH/40g NaOH * 1mol HCl/1mol NaOH * 500g HCl/1mol HCl
= 25.25 g HCl --> 25.5 mL HCl

This answer doesn't make sense in the context of this neutralization reaction. Is there a type of unit analysis that is used specifically for determining the volume required for a reaction?


texts: Why is the discovery of chiral molecules in space a big accomplishment?

texts: Today, I came across the discovery of a chiral pair of molecules in interstellar space. I know that a chiral molecule is a molecule that is not superimposable on its mirror image. But why is this discovery such a big deal?  I think that the existence of chiral pairs should be obvious where multiple molecules exist. So why is this discovery significant?


texts:
We've been told that the in the structure of $\ce{NOCl}$ the central atom is $\ce{Cl}$ (rather than $\ce{N}$) due to some exception.

Looking up on internet I could not find anything to support this. I would like to know if it really exists in such a state due to some exception. If yes, what is that exception.


texts: Identity a metal based on its properties

texts:
A metal X can be cut with a knife. When placed in water, metal X floats and melts. What is X? The options are calcium, copper, magnesium and potassium.

I think it can't be potassium because it will react vigorously with water, So I believe it's calcium. But the only problem is that calcium is denser than water so it will sink.


texts: Perplexing claim in Chang and Overby's "General Chemistry"

texts:
I'm reading the chapter on gases in Chang and Overby's book "General Chemistry: The Essential Concepts" [1, p. 145], and the following passage is causing me some confusion:

The work of the Italian scientist Amedeo Avogadro complemented the studies of Boyle, Charles, and Gay-Lussac. In 1811 he published a hypothesis stating that at the same temperature and pressure, equal volumes of different gases contain the same number of molecules (or atoms if the gas is monatomic). It follows that the volume of any given gas must be proportional to the number of moles of molecules present; that is,
$$V \propto n$$
$$V = k_4 n \tag{5.7}$$

I don't quite understand the emphasized sentence; in particular, I don't understand how the emphasized claim "follows" from the preceding statement. In fact, I don't actually think it does.
For example, suppose instead that the volume of any gas at a given temperature and pressure was inversely proportional to the number of moles of the gas present; that is, suppose the relationship between volume and amount was instead
$$V \stackrel{?!}{=} \frac{k}{n},$$
for some constant $k$. Then it would certainly still be true that equal volumes of different gases contain the same amount of gas. For example, if I had $\pu{5 L}$ of $\ce{H2}$, then, according to the above "false law", I would have $k/5$ moles of $\ce{H2}$. Similarly, if I had $\pu{5 L}$ of $\ce{N2}$, I would have $k/5$ moles of $\ce{N2}$ — the same amount!
So the claim that the proportionality follows from the fact that equal volumes of different gases contain the same number of molecules seems illogical. In fact, it seems to me that the only thing one could logically deduce from the first hypothesis is that there is some relationship between volume and amount which holds for all gases (that is, the relationship doesn't depend on the gas itself).
Am I missing something, or is the statement in the book an error?

Added much later:
To clarify what I'm asking here (though I thought it was pretty clear), consider the following two statements:
Statement A: at a given temperature and pressure, equal volumes of different gases contain the same number of molecules.
Statement B: at a given temperature and pressure, the volume $V$ of a gas is related to the number of molecules by $V = kN$ (where $k$ depends on temperature and pressure).
My point is simply that these two statements are not logically equivalent. B implies A, but not the other way around.
So why is it that the two statements are (seemingly quite often) presented as logically equivalent?
References

Chang, R.; Overby, J. General Chemistry: The Essential Concepts, 6th ed.; McGraw-Hill: New York, NY, 2011. ISBN 978-0-07-337563-2.


texts:
The Wikipedia page on inductive effects states that the order of inductive effects of halogens is as follows:

$$\ce{-F} > \ce{-Cl} > \ce{-Br} > \ce{-I}$$

From this, and from the fact that electronegativity of fluorine is higher than that of chlorine, I guessed that the acidity of p-fluorophenol is more than p-chlorophenol.

But the $\mathrm{p}K_\mathrm{a}$ values are:

p-fluorophenol: 9.8
p-chlorophenol: 9.4

Where did I go wrong? Why does this discrepancy occur? Detailed explanations are very much welcome.


texts: Chemical equation to represent the hydrogen peroxide scavenging experiment, used to determine antioxidant ability of tea

texts: I am currently investigating the antioxidant ability of tea using hydrogen peroxide scavenging. Basically, I will look at absorbance of the tea samples with and without the addition of hydrogen peroxide at 230nm using a UV-Vis spectrophotometer and the difference between both is the amount of antioxidants which were able to reduce the hydrogen peroxide. However, although I've been looking theough many papers, none show me the chemical equation representing this reaction. Could someone help me with this?


texts: How is an aqueous Ag+ the same as [Ag(H2O)2]+?

texts:
$\ce{Ag^{+}_{(aq)}}$ can be written as $\ce{[Ag(H2O)2]+}$ but how would you know that it bonds with 2 water molecules?

I don't get when ligands randomly form 6, 4, 2 bonds.


texts: In order to overlap, orbital lobes must have the same sign of the wavefunction i.e. they must have the right symmetry. In case 2 in the image above, can therefore E2 elimination not occur?


texts: Mechanism of sodium hypochlorite and hydrochloric acid

texts:
The overall reaction for the reaction between NaClO and HCl is: $\ce{NaClO + 2HCl -> NaCl + Cl2 + H2O}$

To try and understand how this reaction occurs, I've thought of a simple mechanism for it. However, I don't even understand my own mechanism. Here's what I proposed:

$\ce{NaClO + HCl -> NaCl + HClO}$
$\ce{HClO + HCl -> Cl2 + H2O}$

The mechanism looks like it could work, but whether it would work is another question.

One problem I have with understanding it is the second step: how exactly would that work? My first thoughts were that since HCl is the stronger acid out of the two, H2ClO+ and Cl- would be produced in the second step, and a third step would have something happen between both of these products to finally produce H2O and Cl2. However, I scrapped that thought since surely an ionic compound would then be produced and nothing would happen afterwards.

Now, I'm lost on what would really happen in the second step.

Maybe I've got it all wrong, but does anyone have any other thoughts on this? Or are there any actual proposed mechanisms for this out there?


texts: Examples to show how useful or not useful of dimerization, trimerization, tetramerization and their likes in synthesizing alkenes and other compounds?

texts:
this answer shows that dimerization is a synthetic method
On wikipedia, 1-octene is showed to made from numerous dimerizations or a tetramerization.
When I read that piperazine  $\ce{C4H10N2}$ is made with ammoniation of chloroethanes or alkanolamines, I wonder if few repeating units synthesis is a general trend for making polyenes and heterocyclic saturated compounds. If dreaming is allowed, could dimerizing ethylamine $\ce{C2H7N}$ with eliminating hydrogen or aziridine $\ce{C2H5N}$ make piperazine?
For the title, I am hesitant to use telomerization or oligomerization because I am unsure about them in the contexts of this question.


texts: Heat of hydrogenation of 1,3-substituted cyclohexanes

texts:
From these two molecules in question, (C) should be more unstable as it is in a cis-configuration. The t-butyl and methyl groups being on the same side of the ring would exert a larger steric force on each other as compared to the trans configuration. However, (D) is mentioned as the correct answer.

How is a trans-1,3 disubstituted cyclohexane more unstable than the corresponding cis-isomer? I drew the chair projections of both compounds and the cis one has both groups on the same side, which would cause 1,3-diaxial interaction as mentioned here


texts:
After reading this recent question I was interested in how to calculate the specific heat capacity of a mixture based on the specific heat capacities of its components.
According to this website the specific heat capacity of an ideal mixture is given by

$$C_{p(\mathrm{mixture})} = \sum\limits_iC_{p(i)}x_i$$
where $x_i$ is the mole fraction of each component.

Where does this come from and what are the assumptions involved in treating it as an ideal mixture?
What deviations from this are observed in non-ideal mixtures? Can you easily predict the deviations based on the mixture and/or predict the actual specific heat capacity?


texts: How to calculate the relationship between the pressures of zinc, carbon monoxide, and carbon dioxide based on mole balance?

texts:
Zinc oxide is reduced at a constant temperature in a closed reactor using $\ce{ZnO(s)}$ and $\ce{C(s)}$ as the only starting materials. The following reactions are assumed to be at thermodynamic equilibrium.
  \begin{align}
\ce{ZnO(s) + C(s) &-> Zn(g) + CO(g)}\\
\ce{2CO(g)   &-> CO2(g) + C(s)}
\end{align}

  Assume ideal gas behaviour. Based on mole balance, the relationship applicable to the system at equilibrium is:
  \begin{align}
\tag{A} P_{\ce{Zn}} &= P_{\ce{CO}} + 2P_{\ce{CO2}}\\
\tag{B} P_{\ce{Zn}} &= 2P_{\ce{CO}} + P_{\ce{CO2}}\\
\tag{C} P_{\ce{Zn}} &= P_{\ce{CO}} + P_{\ce{CO2}}\\
\tag{D} P_{\ce{Zn}} &= 0.5P_{\ce{CO}} + 2P_{\ce{CO2}}
\end{align}

In this problem seeing that none of the given options consisted of $\ce{C(s)}$, so in order to get rid of that I just added the two equations and arrived at the equation $$\ce{ZnO(s) + CO(g) = Zn(g) + CO2(g)}.$$
Now just sort of comparing with the options I find that $\ce{CO(g)}$ and $\ce{CO2(g)}$ are on the opposite sides. It sort of gives me the intuition that may be the pressure term should have had a minus. Anyway I know that I have gone horribly wrong somewhere with regard to my concepts. Please tell me how to solve the problem henceforth.


texts: What are the reaction products of sulfur and potassium nitrate?

texts: YouTube shows videos of dropping a piece of elemental sulfur into molten potassium nitrate and applying additional heat to accelerate the process. A white precipitate falls out to the bottom. There is never any mention as to what this material is. An internet search yields not a clue. Sulfur dioxide is obviously evolved, but KNO doesn't seem to exist if one relies on an internet search.


texts: Synthetic approach for precursor 1,1'-(bromomethylene)bis(1H-pyrazole) in ligand synthesis

texts:
Relevance

During my Bachelor's project I focused on the synthesis of iron(II) complexes comprising a tetrapodal pentadentate ligand from the ligand family $\text{PY5R}_2\ (\text{R = H, Me, OH, OMe})$. [1-4] This ligand consists of one axial pyridine unit and four equatorial pyridine units. I investigated the activity of these complexes in the oxidation of alkenes by hydrogen peroxide.

While doing literature research I discovered several means of tuning the properties and chemical reactivity of these complexes.

For example, the cone angle for steric accessibility is larger for ligands with five-membered pyrazolyl rings compared to those with similarly substituted six-membered pyridyl rings. See the ligand $\text{pz}_{4}\text{lut}$. [5]

Furthermore, one could also influence the donor-strength of the ligand by replacing the axial pyridine unit by a $N$-heterocyclic carbene (NHC) unit. See the ligand $\text{PY4Im}$. [6]

So I thought, why not combine both features? This leads to a tetrapodal pentadentate ligand with an axial NHC unit and four equatorial pyrazole units, abbreviated as $\text{pz}_{4}\text{Im}$.

Figure 1. Tetrapodal pentadentate ligands.

By modifying the procedure employed in the synthesis of $\text{PY4Im}$ [6], the synthesis of the iron complex comprising $\text{pz}_{4}\text{Im}$ would look like this

Figure 2. Synthetic approach towards $[(
\text{pz}_{4}\text{Im})\text{Fe(MeCN)}](\text{PF}_{6})_{2}$.

Problem

My actual problem is related to the starting material.

In the synthesis of $\text{PY4Im}$ [6], 2,2'-(bromomethylene)bis(pyridine) is used as starting material. It is known how to synthesize this compound.

In this synthesis, that of $\text{pz}_{4}\text{Im}$, 1,1'-(bromomethylene)bis(1$H$-pyrazole) I would choose as starting material. However, I cannot find any literature on the synthesis of this particular compound.

Figure 3. 1,1'-(bromomethylene)bis(1$H$-pyrazole) (left) and 2,2'-(bromomethylene)bis(pyridine) (right) - starting materials.

Question

So my question is: Does anyone know a way to synthesize the starting material 1,1'-(bromomethylene)bis(1$H$-pyrazole) for the synthesis of the iron(II) complex comprising the pentadentate NHC-pyrazole ligand $\text{pz}_{4}\text{Im}$?

References

Eur. J. Org. Chem. 2004, 21, 4319-4322.
Tet. Lett. 2012, 53, 1, 54-55.
ChemSusChem. 2016, 9, 10, 1178-1186.
Inorg. Chem. 2006, 45, 15, 6048-6055.
Inorg. Chem. 2008, 47, 17,7468-7470.
Inorg. Chem. 2010, 49, 23, 11223-11230.


texts: Why can some redox half-reactions be combined and some cannot?

texts:
I mean by "combining" is to make a new half-reaction equation and not an overall equation for a reaction in whole.

For instance, I was trying to arrive at the following half-reaction:

$\ce{MnO2(s) + 4H+(aq) + 2e- -> Mn^{2+}(aq) + 2H2O(l)}\quad E^\circ= 1.23\,\mathrm{V}$

by combining

$\ce{MnO4^{-}(aq) + 8H^+(aq) + 5e- -> Mn^{2+}(aq) + 4H_2O(l)}\quad\quad E^\circ=  1.51 \,\mathrm{V}$

and

$\ce{MnO4^{-}(aq) + 4H+(aq) + 3e- -> MnO2(s) + 2H_2O(l)}\quad\quad E^\circ=
1.7\,\mathrm{V}$

using Hess's Law. My calculation yielded +0.19 V, and not +1.23 V as I would expect.

Why caused this? I know that there are half-reactions that can be constructed in this way (as above, by combining two or more other half-reactions) that result in the correct potential being calculated.


texts: Why does formation of bond releases energy and where does that energy come from?

texts: I am having a hard time to imagine why does bond formation releases energy and where does that energy comes from?? It is easy to understand that breaking a bond requires energy because it can be viewed in many ways like breaking a wood into pieces requires energy, ripping your shirt into half requires energy, converting liquid water into gaseous water requires energy. These tangible concepts make it easy to understand why bond breaking requires energy. From these examples it answers the question why does bond breaking requires energy and where does that energy comes from (surroundings/thermal energy/mechanical force applied by the surroundings). But bond formation have so little comparisons and most of the examples associated with it are vague and hard to communicate with non science major. Thanks for the help.


texts:
I had a look at the JCPDS card of BiOCl and saw that there were very small peaks (such as 0.1 percent relative intensity) that I think wouldn't be observed in XRD pattern, they would just blend in with the noise, so I'd like to know how do they calculate the XRD peaks and know their relative intensities so well (this card referenced a 1935 paper).

Many thanks


texts:
This isn't strictly 'pure' chemistry but the knowledge to answer it is probably much closer to chemistry than any other subject.

The question is a simple one - are there any other non-toxic aqueous acids that could substitute for carbonic acid ($\ce{CO2}$ dissolved  in water), that could substitute for carbonates as a basis for an experience similar to soda drinks? I'm thinking of chemical suitability rather than economics. Maybe other weak or organic acids? Or non acids even?


texts:
I am trying to create a small 10 to 20cm cube that can conserve the heat in 100 to 200ml of 60-90c water in a small Pyrex glass for about an hour. The problem is that I can not use commercial insulators like foam, bubble wrap, and the like. I have searched Google for ideas, but all the results are commercial. I also can not heat or cool the device beforehand, and I have to have a 2cm hole in the top.

I have tried cotton balls and a packed cotton balls with felt mixture, and cotton balls worked the best.


texts: Washing stainless steel separator from organic residue

texts:
In my lab we have a stainless steel separator for liquid products of one of our hi-pressure catalytic testing assembly. It is a steel cylinder with two short pipes and one another short pipe with a valve. The problem is, the separator cannot be disassembled and washed. It accumulated organic residues for unknown time, presumably years (it happened before it moved into our responsibility). Some residues were washed with acetone and other solvents, but we want it much cleaner.

Personally, I would love to threat it repeatedly with a strong oxidizer, but I'm afraid that stainless steel might disagree. Also, heating above 200-300 Celsius unfortunately is out of question.

The residue is from Fischer-Tropsch synthesis, so it probably consists of heavy hydrocarbons and possybly some oxygenates and products of their reactions.

Any suggestions?


texts: Is calcium chloride an acidic or basic salt?

texts:
What I reason:
Calcium chloride is the salt of hydrochloric acid and calcium hydroxide. Calcium hydroxide is usually not considered a strong base, and I believe this is because of it's low solubility. $\ce{HCl}$ is a strong acid, and so the salt should be slightly acidic. Wikipedia states the $\mathrm{p}K_\mathrm{a}$ of $\ce{CaCl2}$ is between 8-9, which is in fact slightly acidic, confirming my theory.

What I've experienced:
I've prepared a number of aqueous calcium chloride solutions from distilled water, all of which are purple in the presence of universal indicator and tested with a calibrated $\mathrm{pH}$  probe to be basic. I've tried multiple sources of calcium chloride and each is basic.

TLDR:
Theoretically and literature values state that $\ce{CaCl2}$ is acidic, but my empirical evidence shows that it is basic.


texts: Rate of change and kinetics order of reaction question

texts:
The rate of reaction is given by the following equation, where [Ker-S-S-Ker] is just the molecule being broken down and [RSH] is an abbreviation for thioglycolic acid
The thioglycolate is in large excess and so essentially remains unchanged.

Can somebody explain why the answer is C?
I thought the answer was E (because the rate of change, i.e. the derivative, is equal to the concentration of the reactant itself and so, I thought this signifies a decaying curve?)
Many thanks.


texts: Does corrosion follow the law of conservation of mass?

texts: For e.g .Due to rusting , iron becomes weak .So it should become weak only if the amount of iron is reduced. Even if we say the reduced iron is now the rust ,the amount of rust practically is very less comparing to iron.


texts: Gibbs Free Energy Spontaneity Criterion Derivation

texts:
In Atkins's Physical Chemistry, spontaneity criterion is derived from Clauisius inequality as follows:
Firstly, system is initially at the same temperature T as surroundings. When a change in the system (its state) occurs, there is an corresponding entropy change in the system and a transfer of heat between system and surroundings and Clauisius inequality for this process can be written as: $$dS -\frac {dq}{T} \geqslant 0$$
If process is carried at the same temperature and pressure of a system than $$ dq = dH $$
If we plug dH in Clausius inequality, multiply by T and rearrange what we get is: $$ dG = dH - TdS \le 0$$
Which should prove Gibbs free energy spontaneity criterion for systems at constant p and T. Problem here is that T in the equation for G is of the surroundings not of the system and the whole point of G is to forget about surroundings. Answer you can give to this question is that surroundings and system remain at the same temperature during state change of the system, but if so how can there be any heat transfer between them, for they are already at thermal equilibrium and dq should is zero. When taking Gibbs free energy as spontaneity criterion, system needs to stay at the same pressure and temperature. To keep the system at the same temperature, heat generally needs to be exchanged with the surroundings and if so, heat exchanged with surroundings will change its temperature, so T in Clausius ineqaulity generally is not a constant, it can only be thought as constant if surroundings is uncomparably bigger than the system so that its heat capacity is uncomparably bigger than of system (which in most cases really holds) only in that case T in Clausius inequality can be taken as T of the system. Problem with this is that such an approach gives only approximate solution and equation for G as spontaneity criterion IS NOT AN APPROXIMATION, it holds always regardless of how big system is compared to the surroundings. So, I am not sure this derivation in Atkins's textbook is actually correct for all scenarios not only when surroundings is uncomparably bigger than the system. What are your thoughts?


texts: What is the difference between a polar molecule and polar bond?

texts: I don't understand the difference between a polar molecule and a polar bond. Please explain what the difference between those two is.


texts: A saturated solution is a solution that contains the max amount of solute able to be dissolved. However, can't a solution still be at equilibrium if you add more solute to a saturated solution as long as it doesn't reach supersaturation? What exactly is the requirement (in terms of saturation) for a reaction to be at equilibrium?


texts: What is the logical way to understand Iso, Sec, Tert and Neo prefixes?

texts:
I'm only familiar with Alkanes at a basic level currently.
What seems logical to me is that an Alkyl molecule with the:

"iso" prefix means its an isomer of that alkyl, the usual way i'd see it would be the alkyl group with a substituent (the way an hexane could be isopentane if  I got it right)

as for the "sec" prefix, the alkyl group is connected to the main molecule through a secondary carbon (meaning the carbon on the alkyl is bonded with two other carbons in the alkyl, no consideration given to the main chain here)

I find the "tert" prefix similar to the latter, it is connected to the maine chain through a tertiary carbon (bonded with three carbons on the alkyl)

I couldn't find a basic logical way to address the definition of the "neo" prefix.

Are the ways I described the rest of the prefixes correct?


texts: Will we ever run out of gold, silver, copper and other important conductors?

texts: Conductors are very important in technology. At the current rate of extraction how long until the world's reserves of copper are depleted?


texts: What governs the amount of smoke produced by an extinguished match?

texts:
First Chemistry question, so apologies if this isn't quite in the spirit of this SE.

I have noticed that when extinguishing a lit match by blowing it out, the amount of smoke produced can vary widely. Variables such as how long the match is allowed to burn before extinguishing, and whether it is blown out sharply or with a gentle prolonged draft, appear to influence the amount of smoke that results, but I have not yet been able to make enough observations to establish correlations.

Are there known factors that reliably contribute to the amount of smoke formed by an extinguished match? Is there an "ideal" technique of extinguishing a match that would maximise smoke production?

Thanks!


texts:
My textbook says that $\ce{[CrF6]^{3-}}$ is an example of $sp^3d^2$ hybridization. But I don't really see how. Chromium has an electronic configuration of:

$$3d: \boxed{\uparrow}\boxed{\uparrow}\boxed{\uparrow}\boxed{\uparrow}\boxed{\uparrow} \ 4s: \boxed{\uparrow}$$

Give three more electrons and it might look something like this:

$$3d: \boxed{\uparrow \downarrow}\boxed{\uparrow \downarrow}\boxed{\uparrow}\boxed{\uparrow}\boxed{\uparrow} \ 4s: \boxed{\uparrow \downarrow}$$

This is the ground state of the electrons. I see no way for electrons to be promoted for the formation of six orbitals. And the electrons have to be promoted all the way up to the $4d$ orbital, which would require a significant amount of energy. What is the exact mechanism of bonding in this ion? Amazingly, I couldn't find anything on the Web about this.

EDIT: My textbook also says that $\ce{[Co(NH3)6]^{3+}}$ is an example of $d^2sp^3$ quite similar to $\ce{[CrF6]^{3-}}$. But when I try to understand the exact mechanism, I encounter a similar problem as a I did above.


texts: How do we figure out whether reactions are endothermic or exothermic?

texts:
Are the following reactions exothermic or endothermic:
$$\ce{H2 + I2 -> 2HI}$$
$$\ce{N2 + O2 -> 2NO}$$
So I know the second reaction is endothermic as we need to break triple bonds between nitrogen molecules. I am not sure about the first one. Actually, I want to know if there is some way we can decide whether a reaction is endothermic or exothermic just by looking at the equation?
I got a test coming up in a few months so this was one of the few topics I was having trouble with. Any help would be appreciated.


texts: What is the effect on humans of using dry ice and liquid nitrogen as food additives?

texts:
I have seen on a TV show that some  guy uses dry ice (solid $\ce{CO2}$) to make ice cream and on an another TV show, liquid nitrogen ($\ce{N2}$) is used with tequila.  Both are edible.

I know that both gases are inert, but could these gases (perhaps in larger concentrations) be poisonous or create any side-effects in our body?  If these gases don't create any side effects, what mechanism(s) does the body use to remove these gases from the body?


texts: Is there a known relation between the diffusion of a molecule and the diffusion of the reactants?

texts:
I have a plasma consisting of elements A and B (which have a similar mass). These elements can react to form molecules AB.

$$
\ce{A + B -> AB}
$$

Now if my plasma or gas is expanding based on pressure gradients, I will have some sort of diffusion of these two element concentrations. In fact, this diffusion is the dominant process affecting the concentrations A and B. Based on my spectroscopic analysis, the rate of decay of both elements is similar/the same, so I model them as
$$
[\ce{A}](t) = A_0 \exp(-k_0t) \,, \\
[\ce{B}](t) = B_0 \exp(-k_0t) \,.
$$
Then the concentration of AB changes with
$$
\frac{d[\ce{AB}]}{dt} = k_1 A_0 B_0 e^{-2k_0t}\ - k_2 [\ce{AB}] \,,
$$
where $k_2$ is the rate constant for diffusion. The obtained formula for [AB] is then
$$
[\ce{AB}](t) = \frac{k_1A_0B_0}{2k_0-k_2} \left(e^{-k_2t} - e^{-2k_0t} \right) \,.
$$
This actually fits my data quite nicely, but one thing confuses me: When fitting my data for $[\ce{AB}]$ with this model, the parameter $k_2$ is exactly $2k_0$.

Or rather, they are very close, since the formula has a singularity at $k_2 = 2k_0$.  But if the formula is derived with this assumption directly,  one obtains
$$
[\ce{AB}](t) = (k_1A_0B_0)\, t\, e^{-2k_0t} \,,
$$
which also fits my data very nicely.

I don't understand why $k_2 = 2k_0$ and I am worried that I might say something very stupid in my paper when I try to explain this observation. But this is what I am thinking: $k_2$ is the rate of diffusion for AB, which is twice as heavy as A and B. It will have twice the momentum, which could lead to a doubling of the diffusion rate as well. Does this seem like a probable explanation? If not, which other effects will play a role?

Note that the plasma I am looking at is short-lived and changes constantly, which makes it difficult to apply textbook chemistry to it. Basically all signals I am looking at can be modeled as exponential functions or sums of exponential functions, and sometimes multiple processes might be involved. It's a lot of guesswork, and I am worried that I am actually on the wrong track here. But at least intuitively it makes sense to me that the diffusion of a heavier molecule should happen faster.

Since I was asked why I don't use a more complex diffusion/reaction model: Occam's razor, basically. I don't want to assume too much about my plasma. And I fear that a complex model might contain too many free parameters which would lead to overfitting of the data. (If I'm wrong about this approach, feel free to correct me and explain to me how to go about this. What I do not like are downvotes without a comment telling me what I'm doing wrong. None of the downvotes I have received bothered to do this, which is not helpful.)


texts:
We had the task to solve several salts in water and measure the pH value of the solution. After that we should "create" the protolysis equation and to tell about Chemical equilibrium[s].

I get some possible result equations, but I'm really unsure about them. The [] brackets were used to make the ionic loads easier visible. solving equations:

$\ce{KNO3 <=> [NO3]- + [K]+}$
$\ce{FeCl3 <=> [Fe]^{3+} + [Cl]-}$
$\ce{NH4Cl <=> [NH4]+ + [Cl]-}$`
$\ce{NaHSO4 <=> [HSO4]- + [Na]+}$

my protolysis equations:

$\ce{[NO3]- + H2O <=> HNO3 + [OH]-}$
$\ce{[Fe(H2O)6]^{3+} + H2O <=> [Fe(H2O)5OH]^{2+} + [H3O]+}$
$\ce{[NH4]+ + H2O <=> NH3 + [H3O]+}$
$\ce{[HSO4]- + H2O <=> [SO4]^{2-} + [H3O]+}$

I would say that all equations run bi-directional, because the result of solving equations can vary dependent on temperature for example, and the protolysis equations should be bi-directional because we're having a solution, which isn't a pure acid.

Additionally, I got the question if I can draw conclusions on the pH-change through those protolysis reactions. I would say yes, but not very well, depending on the sum of all hydrogen-containing ions like $\ce{H3O+}$


texts: Differences between ¹³C-decoupled NMR experiment vs a ¹³C-coupled

texts:
How does the acquisition time changes between $\ce{^{13}C}$–decoupled NMR experiment vs a $\ce{^{13}C}$–coupled?

Would the acquisition time be longer if a decoupling of the protons (H) is carried out?


texts: Solubility: Is the common ion effect proportional to individual solubility values?

texts: I'm trying to grasp how solubility works in real applications. Is it so that in a solution with only one salt, it's solubility will change upon the addition of another salt with a common ion in a manner strictly proportional to the latter salt's solubility in water alone? (i.e. that highly soluble salts will decrease the solubility of common ion salts the most and vice versa) If so, is the solubility of each salt in a combined solution a ratio of their respective solubility values when alone in the solution?


texts: What are the chemical reactions behind fire?

texts: I've always wondered what the chemistry behind fire is. What are the basic chemical reactions behind a simple wood fire, and how do they manifest into this phenomenon?


texts: MolView is unable to generate correct 3D structure for hydroxypropadiene

texts:
MolView is unable to generate the correct structure of hydroxypropadiene. It instead generates the structure of acrolein (which has the same molecular formula). Why is this so? Is it because hydroxypropadiene is so unstable that the calculations done while generating the structure degenerate it to acrolein?

MolView is using the default GLMol renderer. Switching to JMol or ChemDoodle does not change the structure.

EDIT: The exact workflow I used was open MolView, delete the caffiene molecule, draw this molecule and click the 2D to 3D button. The generated URL is http://molview.org/?cid=7847, which, when pasted in a browser, interestingly redirects to Acrolein and not the compound that was drawn.


texts: Why refine tar sands oil into petroleum and the rest of the oil processing byproducts rather than burning it directly in the furnaces of private residencies? At least in the snowbelt areas where gas is not readily available.


texts: Dangers of Colbalt Chloride Paper Burning

texts:
I am a science technician and foolishly decided to heat a small amount of cobalt chloride paper on a glass petri dish over a Bunsen. Unfortunately the petri dish broke and the paper hit the metal gauze under and burnt. I immediately put the rest of the paper in water and opened the window.

The cobalt chloride paper was white (not pink) and approximately 3 x 1 cm in size. I am very concerned that I have released very toxic material and would welcome any comments.


texts: Exactly what happens when nitrogen is converted into C14

texts: When a cosmic ray ( neutron) strikes a nitrogen atom in the atmosphere, does the cosmic ray knock one of the nitrogen electrons out of its orbit and into one of the protons in the nitrogen nucleus? Does the cosmic ray just continue on its way through the atmosphere? Is the electron that got knocked out of orbit absorbed  into the proton making it become a neutron? And when radioactive decay occurs in the c14, does the neutron that used to be a proton spit out an electron that becomes part of that atom or does it go out into space?


texts: I am currently playing a dungeons and dragons campaign in which there are some new elements. My party, being the nerds that we are, is looking to experiment with them and attempt to discover new ones using a spectroscope. The problem is that we need a solvent that will dissolve our sample. I was wondering if there were any suggestions as for what to use, or how to obtain it, as the game takes place in a medieval time period. Acetone would be best, but I'm not sure that it's possible to extract that from nature, although it does occur naturally. Thanks!


texts: Oxidation of water by permanganate: Does this reaction happen?

texts:
Since MnO4- is a strong oxidiser, if one increased its concentration  relative to water, could it oxidise the water (Le Chatelier's Principle seems to suggest so)?

I have attempted to write the possible (redox) reaction, but I fear I've gone terribly wrong:

$$\ce{MnO4^{1-} + 2H2O -> 2H2 + 3O2 + Mn^{3+}}$$

Can someone tell me if I've constructed the equation (and balanced it) right? If not, can someone offer me some guidance in this regard?


texts: How can I calculate the boiling temperature of a pure substance as a function of pressure?

texts: I want to make an algorithm that will give me the boiling temperature of a substance as a function of pressure, the critical temperature of a substance, and the critical pressure of a substance. I believe this can be done using a combination of the Peng-Robinson Equation of state and the Clayperon or Clausius-Clayperon equation of state. The issue is that I believe this requires additional input criteria, specifically the latent heat but this function is supposed to be more general. Is there any way to work this method without the latent heat, or to calculate the latent heat from the other known values?


texts: Why doesn't the expermintal molar solubility match the one calculated by the Ksp value?

texts:
For $\ce{HgCl2}$ ($M = \pu{271.52 g mol-1}$), the reported $K_\mathrm{sp}$ value is $10^{-15.69}$.

This means that the calculated molar solubility of $\ce{HgCl2}$ in water is $(10^{-15.69}/4)^{1/3}\cdot\pu{271.52 g mol-1} \approx \pu{0.0010 g L-1}$, or equivalently, $\pu{0.010 g cm-3}$.

However, in Pubchem, the reported molar solubility is 6.9 g/100 cc. What is the source of the large deviation between the experimental and the theoretically calculated molar solubility of $\ce{HgCl2}$?


texts: Calculating molarity of a gas using ideal gas equation

texts: Is hydrogen gas at 1 atm pressure and 298 K temperature considered as a 1 molar solution? If yes then can I use ideal gas equation $$PV=nRT$$ to find molarity as $$\frac nV = \frac P{RT}?$$


texts: What is the complete mechanism of reaction for sodium benzoate and ascorbic acid?

texts:
What are the complete steps of reaction from sodium benzoate and ascorbic acid to benzene? I can't seem to visualize it, and, much less, find anything online regarding the actual steps of the reaction.

Additionally: how does it make use of, say Cu(II) or Fe(III) to complete the reaction? It seems that the reaction can only proceed with these present.


texts:
In Helen Tweeddale's article,[1] they labelled metabolites of E. coli with [U-$^{14}$C]glucose. What sort of glucose is it? I understand they used isotope 14, which is radioactive but what does the U stand for?

Helen Tweeddale, Lucinda Notley-McRobb, and Thomas Ferenci, J Bacteriol. 1998, 180(19), 5109–5116. PMID: 9748443 (pdf)


texts:
What is the Schrödinger wave equation?
What are radial probability functions, nodes-angular and radial and electron cloud?

I am really confused with all these terms and all my book seems to offer me is a set of very complex words and definitions. I am relatively new to atomic structure and related things, so a brief answer in simple words would really be helpful!

I also would like to know more about Hamiltonian and Laplacian operators and related subjects.


texts: If I have varsol in a tank and methanol is put into the same tank will methanol rise to the top or will it separate? Or will it mix together ?


texts: Is temperature double-counted in the Gibbs free energy equation?

texts:
Complete amateur here. When looking at one form of the equation deriving the change in Gibbs free energy for a given chemical reaction, the terms change in enthalpy, and the negative product of temperature (in kelvin) and change in entropy:

$$\Delta G = \Delta H - T\,\Delta S$$

This seems to double count how temperature will influence the spontaneity of the reaction if temperature is already considered when deriving entropy, $S$.

Any guidance would be appreciated.


texts: How can I measure the amount of CO2 in grams in a known volume of soda based on its weight?

texts:
We have a soda machine that can fill either still water or soda. In both cases the amount is 400 ml in the beaker, but the soda weighs a little less.

How can we use the volume X = 400 ml and the weight Y = ?? grams to determine the amount of $\ce{CO2}$ in the solution?


texts: Which stabilizes a carbocation more : Back Bonding or Conjugation?

texts:
Suppose we take these two compounds:

The first carbocation can rearrange to produce the second one by hydride shift. Which is more stable ? Why ?


texts: Is there a clear distinction between the various intra- and intermolecular interactions?

texts:
Wikipedia lists dipole-dipole, hydrogen bonding and Van der Waals under intermolecular interactions, and hydrophobic, ionic and covalent under intramolecular interactions.

Is there a clear distinction between each and every one of these interactions? For example: isn't hydrogen bond a private case of VdW? aren't ionic bonds and hydrophobic interactions private cases of dipole-dipole interaction?
Is there one single chart that differentiates all of these types of interaction?


texts: What happens in the attempted diazotisation of 1,2-diaminobenzene?

texts: Usually, $\ce{NaNO2}$ and $\ce{HCl}$ are the reagents used to generate an aryldiazonium chloride from an aniline. However, in this compound there are two amine groups adjacent to each other, so it seems unlikely that a diazonium chloride would form. Is it possible for the two amine groups to react during the reaction and form some cyclic product?


texts: Is an SN1 reaction an elementary reaction/one step reaction?

texts:
I need some help. From what I understand, elementary reactions are reactions which only has one transition state. Another definition that I have come across is that elementary reactions obey the rate law.

I believe that $S_N1$ are NOT elementary reactions because they proceed through more than one transition state. However I am not so sure about the other definition (the rate law one). Could someone explain to me what exactly an elementary reaction (or a one step reaction) is? And can someone explain to me if an $S_N1$ reaction is an elementary reaction or not.


texts: Can I determine purity of isopropanol with a hydrometer?

texts: Assuming I start with a known 99.8% purity of isopropanol, after recovery with a distillation apparatus, could I use a hydrometer to test for water content? If so, is there a special one I should use?


texts: Can the degree of dissociation of a weak acid be more than 1?

texts:
My common sense dictates that it can't be more than 1 because after all it is the number of moles dissociating per mole of a substance.
But I was reading about Ostwald's law of dilution and came across this formula:
a (degree of dissociation) = √K/√C
So if C is less than K by about 4 times, a becomes 2.
I'm sensing there's an extremely simple solution to this question but can't realise what it is.


texts: Is it safe to mix methylated spirits with isopropyl alcohol?

texts:
I have about 200ml of methylated spirits and 500ml of 100% isopropyl alcohol that I want to mix together in a plastic drink bottle.  I will use it for fuel in an alcohol burning stove while camping.  I can't seem to find any other information about mixing them so...

Is it safe to do so?
Is a clear plastic drink bottle OK to keep them in? (worried about melting the bottle - adverse reaction)
If it is safe to mix them, will I end up with a more flammable mix?

Thanks for any help!


texts: Is it possible to obtain the amount of air required for a combustion analysis?

texts:
I'm not very sure if the required amount of oxygen (I assume) can be found by only knowing the amounts of the produced subtances after a combustion.

To illustrate this I found this problem:

  $1.14\,kg$ of octane $C_{8}H_{18}$ is burned with a certain amount of
  air. The resulting products from the combustion are known to have the
  following percentages by volume: $CO_{2} = 41.18\%$ ; $CO = 5.8%$ ;
  $H_2O_{(vapor)} = 52.94\%$. Find the weight of required air in
  kilograms. Assume the composition of the air in this combustion is
  $21\%$ of $O_{2}$ and $79\%$ of $N_{2}$ by volume and its average
  molecular weight is $28.8\,\frac{g}{mol}$.

The alternatives given are as follows:

$\begin{array}{ll}
1.&9.0\,kg\\
2.&16.4\,kg\\
3.&12.5\,kg\\
4.&45.1\,kg\\
5.&120\,kg\\
\end{array}$

What I think to approach this problem was to use the given percentages to get the number of moles using the initial moles of octane.

Using these moles I can obtain the grams of oxygen produced. Since it is given the percentage which is of oxygen in the air I could use this to find the required mass of the air to get that amount of air.

This is shown as follows: (for the sake of brevity I'm ommiting units but they are consistent.)

$\textrm{FW of octane} = 114$

$n_octane=\frac{1140}{114}=10$

Then moles of each product:

For $CO_{2} = 41.18\%$

$\frac{41.18}{100}\times 10 = 4.118$

Then in this amount of $CO_{2}$ there must be these grams of oxygen:

$4.118 \times \frac{32\,g\O}{1\,mol\,CO_{2}}= 131.776 \,g$

For $CO = 5.8\%$

$\frac{5.8}{100}\times 10 = 0.058$

$0.058 \times \frac{16\,g\O}{1\,mol\,CO}= 0.928 \,g$

For $H_2O_{(vapor)} = 52.94\%$.

$\frac{52.94}{100}\times 10 = 5.294$

$5.294 \times \frac{16\,g\O}{1\,mol\,H_2O}= 84.704 \,g$

Adding these together:

$131.776+0.928+84.704=217.408\,g\,O$

Then using the known percentage of oxygen which is $21\%$

$\frac{21}{100}x=217.408$

$x=1035.28 \,g$

Which is approximately 1.035 kg. but this answer doesn't get any close to the specified alternatives. Did I overlooked something. Or could it be that this approach is not applicable?. In this given situation is it possible to find the required mass of air?.


texts: Is 4-methylchlorobenzene an acceptable IUPAC name for this compound?

texts:
The answer given for this is A and B
My doubt is if toluene is an accepted IUPAC name then why not chlorobenzene?(If that is the reason why the answer is given wrong)

Or else is there any other reason why the option C is wrong?


texts: Confusion in understanding temperature change in exothermic reactions

texts:
The question due to which my doubt arose $\ce{->}$

  The following system is in equilibrium:
  $\ce{SO2Cl2 + {Heat} -> SO2 +Cl2}$

  What will happen to the temperature of the system initially if some $\ce{Cl2}$ is added into it at constant volume ?

My attempt at the question : Since if we add more $\ce{Cl2}$, concentration of products will increase which will in turn shift the equilibrium in backward direction, which will in turn release more heat. And since the heat is being released to the surrounding, temperature of the system should decrease.

Though according to my textbook the answer is temperature of the system will increase.

So please do explain where my understanding is wrong.


texts: Clarifications on thermodynamic cell efficiency

texts:
The thermodynamic efficiency of any cell (especially Fuel cells) is given as $$\frac{\Delta G}{\Delta H} \times 100$$

I understood this partly, that since $\Delta G$ is the useful work obtained in the ideal case, the efficiency expression must have it in the numerator. But I fail to see the intuition (or maths) behind the $\Delta H$ term in the denominator. I have two questions regarding this:

On applying this equation to ordinary (not fuel cells), for a general reaction $$\ce{A^+ {(aq)} + B {(s)} -> A {(s)} + B^+ {(aq)}}$$ the $\Delta G$ term is given as $-nF E_{\text{cell}}$ where $E_{\text{cell}}$ depends on the concentration of the two ionic species as given by the Nernst equation $\left(E=E^\circ-\frac{RT}{nF}\ln\frac{[\ce B^+]}{[\ce A^+]}\right)$. On the other hand, is the $\Delta H$ term independent of the concentration? and if not, how would it (and consequently efficiency) depend on the ionic concentrations?
For fuel cells, suppose the cell reaction is such that the $\Delta S$ is positive and since $\Delta G=\Delta H -T\Delta S$, therefore $|\Delta G|>|\Delta H|$ since the second term in the equation for $\Delta G$ becomes negative due to positive entropy change. Would this predict an efficiency greater than 100%?


texts: Order of stability of substituted benzyl carbanion

texts:
I think the order should be II > III > I. The +m effect should be more in case 1 than in 3, isn't it ? So, 1 should be more unstable than 3.

Someone please explain.


texts: What is the use/importance of the equilibrium constant Kc

texts:
I understand what the equilibrium constant is, however when reading in my textbook it has occurred to me that I do not understand what it's actual use/importance is. One specification in my syllabus is "Understand the importance of the numerical value of Kc".

Thank you for any help.

I do not understand why this question has been put on hold. How can I demonstrate that I have put in an effort into understanding this question when I literally cannot find the answer on the internet or in any of my four textbooks? I have familiarised myself with Kc, however nowhere can I find it's importance, hence the reason that I ask the question.


texts: Why does a first order reaction only depend on the concentration of a single reactant?

texts:
I am new to kinetics so please explain it from basic, If there is a reaction  -

$$\ce{A + B + C -> D}$$

In first order reaction rate is given by-

$\mathrm R = k[\mathrm A]$ or $\mathrm R = k[\mathrm B]$ or $\mathrm R = k[\mathrm C]$

my question is why cant $\mathrm R = k[\mathrm A]^{1/3}[\mathrm B]^{1/3}[\mathrm C]^{1/3}$
 even though order of reaction is still $1$,----- is it by definition that 1st order reaction always depend on concentration of single reactant, or is there any experimental proof for this?.


texts: What effect is on the rate and rate constant when concentration or temperature increases/decreases?

texts:
I have a few questions regarding rate and rate constant. I am wondering what effect certain concentrations, temperature, etc., has on rate and rate constant. Would be of great help if you can clarify this for me!

If a concentration was halved (and all other factors remained the same), does that mean rate would decrease? If instead the concentration was doubled, I would assume that it would also double.
For rate, if the temperature of the solution decreased, does that mean that it would also decrease since it means it would take less time?

For rate constant, if the concentration was halved, I think there would be no effect (because concentration effects rate only). But, what if the concentration was doubled, does that also mean that there's no effect or would the rate constant decrease?
For rate constant, let's say the ionic strength of the solution increased. Does that mean that the rate constant decreases?

Thanks for clarifying!


texts:
How could 1,4-butanediol be converted to 1,4-butandial (succinic aldehyde)? I thought of simple oxidation with $\ce{CuO}$ but apparently it yields gamma-butyrolactone according to erowid
and this paper$\ce{^{[1]}}$. Could increasing the pH result in the formation of 1,4-butandial?
$\ce{[1]}$: Romaric Gérardy, Romain Morodo, Julien Estager, Patricia Luis, Damien P. Debecker, Jean-Christophe M. Monbaliu, Sustaining the Transition from a Petrobased to a Biobased Chemical Industry with Flow Chemistry, Topics in Current Chemistry, 10.1007/s41061-018-0222-3, 377, 1, (2018). (DOI)


texts:
During hydrolysis of a halide of carbon via $\mathrm{S_N2}$ mechanism, the incoming neutral water molecule attacks the partially positive carbon centre from the side opposite to the halide side and forms a transition state where the hybridisation of centre is $\mathrm{sp^2}$. The nucleophile and the leaving group (halide) thus are attached to opposite sides of the same p orbital (now elongated). Ultimately the nucleophile kicks off the halide from the back.

But when we are carrying hydrolysis on $\ce{PCl3}$ (phosphorus trichloride) why does the water attack an empty d-orbital of the central phosphorus atom and not do the same mechanism as it does in the previous case mentioned. Why can't the attack take place like above leading to formation of an elongated p orbital?


texts:
I recently started a small project of making home-made chromium alum crystals, as can be found on many sites, videos and recipes all around the internet.

I tried calculating the amount of salt I needed from wikipedia's page for the chromium alum, and then went nowhere, since the solubility data stated there does not say if it is for the dodecahydrate or anhydrous form. I tried it for the dodecahydrate and failed since no seed crystals formed after two days.

Then I added about 100% more alum to the solution while heated to about 80°C (not measured) and it all dissolved, and then after some hours some nice seed crystals formed.

After the initial seed crystal creation, I was left with a small amount of saturated solution and some extra seeds that I wouldn't use.

Just for curiosity sake, I then went to try to heat this solution to boil of the water and try to make some anhydrous chromium alum, or at least the solid, crystalline hydrated form.

Then, first, the solution took a goopy, molten plastic-like appearance, and then, after several hours, it went from a dark purple (hydrated?) clumpy mass to a greyish-green colored powder that didn't change at all even at the maximum temperature of my (bad quality) hot plate that hovers around 250°C.

I believed to have made anhydrous chromium alum (wikipedia stated that it is a greyish-brown powder), and then proceeded to take a small sample of this powder and re-hydrate it.

To my surprise, it didn't dissolve in distilled water at all! Having read something somewhere about some salts being quite soluble in water but dissolving very slowly, I then waited several days, stirring it occasionally, and nothing changed.

What happened to my chromium alum?

Wikipedia states a melting point of 89°C that could be related to the plastic-like melt observed, but also states a boiling point of 400°C that while I was never able to observe since my hot plate never reaches anything close to this temperature, should have left me with molten chrome alum. I know some compounds increase  in viscosity with temperature increase, so I wouldn't be surprised to not get  a flowing liquid.

But instead I got a greyish-green powder at around 250°C that is not water soluble.

Wikipedia also does not state decomposition temperature for this compound.


texts: Alternating heavy metal materials analysis

texts:
If someone had a material that was made of alternating heavy metals (ABAB) and each layer was 1 micrometer thick, would an electron beam be able to displace electrons in the lower layers? If these electrons in lower layers were displaced, would these automatically have to be backscattered electrons since they came from a deeper place?
Or would it be better to use X-rays in this case? Would x-rays be able to penetrate through a few layers of metal?


texts: What is/are the product when this reacts with Lucas reagent?

texts:
What would be the product(s) if this alcohol reacts with Lucas reagent?
Would Methyl shift happen ? I heard that in Groove's process, only primary and secondary alkyl chlorides are formed.


texts: Conceptual tussle with kinetics of equilibrium and non-equilibrium processes

texts:
Prologue:
Recently started with Chemical Kinetics at class. Came across a couple of points in Levine's Physical Chemistry (the book was recommended on Chem.SE; so I thought I'd give it a read :D) that I'm having serious issues wrapping my head around. This query is about the kinetics of equilibrium (and non-equilibrium) processes, and the fact that this has puzzled me for quite a while... I attribute to my (seriously questionable) understanding of equilibrium processes (courtesy: High-school education). It would be prudent to keep my shortcomings in Kinetics (newbie) and Equilibrium (possibly flawed understanding) in mind while addressing my query in your answer or the comments section. Thanks!

According to Physical Chemistry (Levine,I.N), Chapter 15, "Kinetics":

Processes in systems in equilibrium are reversible and are comparatively easy to treat. This chapter and the next deal with non-equilibrium processes, which are irreversible and hard to treat. The rate of a reversible process is infinitesimal. Irreversible processes occur at nonzero rates.

Which, if I understood correctly, can be paraphrased as:

Equilibrium processes are reversible and have infinitesimal (practically "non-existent") rates.
Non-equilibrium process are irreversible and have non-zero ("finite" or "significant"?) rates.

From my "understanding" of Equilibrium; chemical equilibrium is an example of dynamic equilibrium. When a chemical reaction, $$\ce{A + B -> C + D}$$
has proceeded to equilibrium. The "forward" rate of reaction (rate at which $C$ + $D$ is spit out) must equal the "backward" rate of reaction (rate at which $A$ + $B$ is spit out). There is no net formation of products/reactants, but both the forward and backward rates are positive and finite.

My question?
Why does Levine say that equilibrium processes have "infinitesimal" (almost non-existent) reaction rates? I thought the forward and backward reaction rates in a reaction at equilibrium are finite...


texts: Can physical absorption happen despite the formation of products?

texts:
As far as I know, the absorption of $\text{SO}_2$ in water goes under physical absorption, meaning the sulfur dioxide bubbles are held in place by Van der Waals forces, in this case Keesom forces, since both water and sulfur dioxide molecules are dipoles. This table classifies the absorption of sulfur dioxide in water as physical absorption, taken from this site.
However, sulfur dioxide does create products (within an equilibrium) with water.
$$\ce{SO2 + H2O ⇌ HSO3^- + H3O+}$$
and
$$\ce{SO2 + OH- ⇌ HSO3^-}$$
Now, with chemical absorption, the absorbate is held within the absorbent due to interfacial chemical bonding. Could it be that these products don't aid with the absorption at all? Or, could it be that they aid with the absorption in conjunction with, but perhaps to a lesser degree than, than the Keesom forces, thus making the absorption more physical than chemical? If so, is this perhaps the norm?
Or, is this absorption actually a chemical one?


texts: Chemical methods to extract Oxygen from Rust

texts:
Let's say I have a large quantity of rust and want to extract the oxygen from it in a way that allows me to collect the oxygen in a container.

What chemical process can I use to do this and what equipment does it require?

It's preferable if the process is doable at home so I can demonstrate the process but it's not mandatory.


texts: Does a reaction proceed through SN1 if rearrangement results in a stable carbocation?

texts:
While going through my book I came across the following problem:

I thought it was safe to assume that the secondary alcohol would give $S_N1$(although secondary alcohols give significant amount of both $S_N1$ and $S_N2$) but I was sure that the 2nd reaction would proceed through $S_N2$ since it was a primary alcohol.
But it turned out to be the opposite as my book said that both would proceed through $S_N1$. Why does this happen?

The products shown were also rearranged. But isn't rearrangement a thing that happens after the carbocation has already formed?
And if the carbocation is 1 degree, then why would it form at the first place?
How does the compound know that it can rearrange once it forms the less stable carbocation, so it compromises some stability to gain more?


texts: Condensation Rate is Increased with a Decrease in Temperature?

texts:
I'm having trouble understanding why the rate of condensation is increased with a decrease in temperature. My reasoning is as follows:

If...

The rate of condensation (R) depends on the concentration of gas molecules (reactants), and it's defined as:

R = k[Gas]

And...

Any rate is proportionate with respect to temperature; as is k...

Then why would a decrease in temperature increase the rate of condensation (R)?

My deductive reasoning for this is as follows:


texts: Is saturated vapor pressure equals to saturated vapor partial pressure?

texts:
I got confused for this two things, the first pressure is the pure water vapor in a certain temperture, and the second vapor partial pressure is the water vapor existed along with other gases, so my question is,
Is the maximum vapor partial pressure in the air the same thing as the pure water vapor pressure, the first one is among different gases, and the second is between liquid/gas phases.


texts: Finding final pH of the buffer solution without applying Henderson equation

texts:
A is beaker with $\pu{0.1 M}$ $\pu{25 cm^3}$ solution of $\ce{NH3}.$ B is beaker with $\pu{0.1 M}$ $\pu{5 cm^3}$ $\ce{HCl}.$ Now the solution of A and B is mixed. What will be the final $\mathrm{pH}$ of the mixture? $K_\mathrm{b} = \pu{3.3E-5}.$

I believe the mixture will become a buffer solution and we should use Henderson equation to solve this.
$$n(\ce{NH3}) = \pu{0.1 mol L^-1} × (\pu{25E-3 L}) = \pu{2.5E-3 mol}\tag{1}$$
$$n(\ce{HCl}) = \pu{0.1 mol L^-1} × (\pu{5E-3 L}) = \pu{5E-4 mol}\tag{2}$$
$$\mathrm{pOH} = \mathrm{p}K_\mathrm{b} + \log\frac{n(\ce{NH4Cl})}{n(\ce{NH4OH})}\tag{3}$$
$$\ce{NH3 + HCl -> NH4Cl}$$
$$n(\ce{HCl}) = n(\ce{NH4Cl}) = \pu{5E-4 mol}\tag{4}$$
$$n(\ce{NH3}) = n(\ce{NH4OH}) = \pu{2.5E-3 mol} - \pu{5E-4 mol} = \pu{2E-3 mol}\tag{5}$$
$$
\begin{align}
\mathrm{pOH} &= \mathrm{p}K_\mathrm{b} + \log\frac{\pu{5E-4 mol}}{\pu{2E-3 mol}}\\
  &= 4.4819 - 0.602\\
  &\approx 3.88 \tag{6}
\end{align}$$
$$\mathrm{pH} = 14 - \mathrm{pOH} = 14 - 3.88 = 10.12\tag{7}$$
However, the book from which I am solving this problem suggests that this problem should not be solved by Henderson equation without providing any reason. Can anyone tell me why this solution should not be considered a basic buffer? I would really appreciate some opinion on this.
P.S. The problem was given in Bangla. I tried my best to translate it. This is an admission question of KUET-2019 Bangladesh. My textbook has this question, but I'm not sure about the solution. Please note that this is an admission question of previous year (2019).


texts: Stereochemistry of product in Diels-Alder reaction

texts:
I have a few questions on this problem I solved:

1) Why does carbon "b" on methyl vinyl ketone attack carbon "5" on the lactone? Why not carbon "2"?

2) The answer key says that the end product should have "trans" stereochemistry. The internal ester group should be opposite the carbonyl group as shown in my picture. Why is this the case? Does this have to do with the endo rule?


texts:
The energy of molecule orbitals increases with more nodal planes. W1 (in the attached picture) has no nodal plane. I'd like to know how to draw the nodal planes in cyclopropane molecule orbitals but do not know how. I found no picture in the web with the nodal planes of cyclopropane.

How many nodal planes have W3, W4 and W5?


texts: Python command line tool to get chemical structure

texts:
In computational chemistry, we need to provide an starting molecular structure to start our calculations. Is there any way to get that from a chemical database? Say, I want to run H2, it would call something like

url="www.chemicaldatabase.com"
H2=(url,H2)

or it can use smile/other standard symbols for chemical representation.


texts: What are the products formed by the thermal decomposition of DMPA photoinitiator?

texts: I am using DMPA as a photoinitiator for my experiments to polymerise acryamides  and actylates. I need to know if the DMPA used for the purpose forms any decomposition products if heated at high temperature. I tried to search the literature but could not find any useful information. If anyone knows and could help me I would really appreciate that!


texts: Reaction of perchloric acid with cyclopropenol

texts:
Question:

Identify A and B.

My attempt
The first step will be the attack of $\ce{PhMgX}$ on carbonyl carbon, that is, 1,2 position followed by hydrolysis, yielding an alcohol.
But how does the reaction proceed with $\ce{HClO4}$?


texts: Modern open-source tools for simulation of NMR spectra

texts:
I am interested in predicting the NMR spectrum of small organic compounds.  It doesn't matter to me if the prediction is very accurate.  I'll eventually be comparing the prediction to experimental results.

It looks as if several free online tools offer the ability to do such predictions:

NMR DB is a free website that offers a prediction of 1H, 13C, and supposedly even 2D NMR experiments.  Structures are entered via a GUI editor.
VeSPA and PyGamma are Python packages (or Python wrappers around C libraries) that supposedly simulate NMR spectra of molecules.  However, both packages are very old and have not been substantially updated in some time.

My question is, what is the best available (free) computational tool for predicting NMR spectra?  As I mentioned, I understand that predictions are imperfect.  What software, if any, are widely used by practicing chemists for NMR simulation?  What is the best reference to read about such software, including the heuristics and algorithms it uses to simulate spectra?  Is Vespa and/or PyGamma state of the art?  The NMR DB site is nice, but I'd very much prefer an interface that is amenable to scripting, and where structures could be supplied computationally rather than via a GUI interface.

(I'm a mass spectrometrist and biochemical engineer with little training in NMR methods.)


texts: What is the oxidation mechanism of gunpowder?

texts:
I've been recently looking into fireworks and the chemistry of explosives, and I found out that, amongst others, one of the most important reactions in gunpowder ignition is the oxidation of charcoal and sulfur by $\mathrm{KNO_3(s)}$. I am curious as to whether it is known if this reaction occurs between charcoal/sulfur and solid state potassium nitrate or if the potassium nitrate decomposes first and the reaction occurs via gaseous oxygen as an intermediate.

Is there a general mechanism of oxidation between solid oxidizing salts and organic matter/sulfur? Does the same thing happen with $\mathrm{KClO_3(s)}$ or $\mathrm{KMnO_4(s)}$ for example?


texts: I work a lot with Urea-Formaldehyde resin/plastic, both in carpentry and textiles. Cleanup while still uncured is simple enough. Cleanup before even mixed is easy enough. What I don't know, is how to cleanup plastic that has set and cured. If it was reasonably safe to guess and try, I would, but in this environment/conditions acetaldehyde formation is very possible, which makes release formaldehyde a problem. Grinding or sanding the plastic is not an option. I haven't seen a MSDS say anything about cleaning up cured plastic. From accidental spills it doesn't seem to disolve in xylol, acetol, or toluol. Anyone have any ideas? As long as there is a preditable outcome I have the resources to test just about anything.


texts: Is there a characterisation for conjugated dienes similar to cis-trans?

texts:
As shown above,we know there are two configurations possible for conjugated dienes.

Are they given any special names like we have cis and trans?
This came up because while studying the Diels Alder reaction, it occured to me that maybe only the 'cis' like dienes will go through the reaction.


texts:
I read an article about Buffer capacity

The reaction is:

$\ce{HA <=> H+ + A-}$

They have given that:

But shouldn't $C_{buf}=[HA]+[A^-]+[H^+]$ ?

The total concentration at equilibrium is $c(1-\alpha)+2c\alpha=c(1+\alpha)\neq c$. Hence the initial concentration of buffer is different from that at equilibrium.


texts: How does an additive like aluminum oxide make a material like polyurethane harder/more resistant to wear?

texts:
I have wood flooring which is coated with a polyurethane finish. According to the marketing, aluminum oxide has been incorporated into the polyurethane to make it more durable, but that's all that is said about it.

I understand that aluminum oxide is a hard substance, but I don't understand how it could be incorporated into a polymer to improve wear resistance. If it occurs as microscopic beads or granules of alumina within a polymer matrix, how does that confer durability? I can understand how a coating of alumina on top of the polymer would provide durability, but how could that even work?

So, my question is: What form does the alumina take in the end product and how, in that form, does it improve durability?


texts: Does Hybridization change the shape of molecules after bonding to other molecules?

texts:
If you have two molecules bonding to each other such as NH and CH2 you have a change in hybridization for both N and C.
NH with its two lone pairs is sp2 hybridized and CH2 is also sp2 hybridized.  As the molecules begin to bond, the Nitrogen changes to sp hybridized and the CH2 changes to sp3 hybridized.  First of all, is this correct?
Secondly, does this shift in hybridization result in a change in the orientations of the atoms?  For example CH2 is bent, but in the combined molecule it should be trigonal planer? I.e. 120 degrees between the H atoms?
Thanks for any help!


texts:
Why does acetone have a lower boiling point than hexane? I thought that since hexane is non-polar then it should have weaker intermolecular forces and a lower boiling point, but it doesn't. Why?

For reference, the boiling point of acetone is roughly 56 °C  while that of n-hexane is roughly 68 °C.


texts: The unit cell in a body centered cubic lattice is given. Each sphere has a radius r and the cube has a side a. What fraction of the total cube volume is empty?


texts: Horizons of a bachelor degree in chemistry

texts: If I have a bachelor degree in chemistry, what master programmes can I apply for ? In other words, are the choices limited in chemical engineeirng, biochemistry,etc? Is it possible to apply for a master degree in computer science for example ?


texts: The freezing points of heavy water (3.8 °C) and tritiated water (4.49 °C) both seem to be well-known. I can't find anywhere that gives the freezing points of $\ce{H2^18O}$, $\ce{D2^18O}$, or $\ce{T2^18O}$, though. Are any of these values known? If not, is it at least known whether they'd be higher than with ordinary oxygen?


texts: What is the hybridisation of the carbons in the allyl radical?

texts:
The example I am talking about is $\ce{CH2CHCH2^.}$.

To find the steric number and hence the hybridization, we use steric number  = No. of lone pairs + number of sigma bonds. In this example, the last C atom has only one electron. Should we count it as a lone pair?

My teacher says that that electron will get delocalised so its hybridization will be $\mathrm{sp^2}$ and not $\mathrm{sp^3}$ (which I think is true). I didn't understand the delocalisation stuff. Is it true that here, there will be delocalisation and if not then what is happening here? If delocalisation is occurring here then please explain it too! Also please tell me in which cases is there delocalisation of electron(s)?

My teacher also said that had it been $\ce{CH3CH2CH2^.}$, then there would be no delocalisation of electrons. Why does this happen?


texts: Chemical Formulae and the Periodic Table of Elements

texts:
Reading about heavy water, I have found that the chemical formula for it can be written 2H2O or D2O.

  Deuterium is an isotope of hydrogen that is found in large quantities in water, more than one atom per ten thousand hydrogen atoms has a deuterium nucleus. The isotope is denoted “2H” or “D”, and is normally known as “heavy hydrogen”. Deuterium is used in a number of conventional nuclear reactors in the form of heavy water (D2O), and it will probably also be used as fuel in fusion reactors in the future (Source: ScienceDaily).

Encyclopædia Britannica says the formula can be 2H2O.  Is this correct?

2H (or 2H) = D is interesting to me as D is not in the periodic table of elements.

I thought that formulae should be formed using the symbols within the periodic table.  What are the rules surrounding these chemical formulae?


texts:
For example, let us that say we have a question where we have to use the ideal gas law and that the moles and temperature are constant. Then the gas law can also be written as $$nRT=PV$$ However, according to my solutions manual, this can also be written as $$nRT=P_1V_1=P_2V_2$$

My question is, how are we justified in rearranging the equation like this?


texts: How do I explain these bond angles in SF4 and SOF4?

texts:
From here and here I found that the bond angle between the equatorial $\ce{F}$'s  in $\ce{SF4}$ is less than that in $\ce{SOF4}$. I understand that is because of greater repulsion by lone pair than by double bond.

But the angle between the axial $\ce{F}$'s  in $\ce{SF4}$ is more than that in $\ce{SOF4}$. I am not able to understand why is this so. Shouldn't the lone pair repel more than double bond here too?


texts: Which is more stable: Ortho or Para Hydrogen?

texts:
It is known that Para-Hydrogen has opposite spin and Ortho-Hydrogen has same spin.
Therefore, the energy of Para-Hydrogen is lower than that of Ortho-Hydrogen.
Therefore, the stability order should be: Para-Hydrogen > Ortho-Hydrogen.
Is this true or is the stability order the opposite of what I predicted?. What is the reason for this stability order?


texts:
I'm a high school student with basic knowledge about chemical thermodynamics. I have three questions regarding the thermodynamic state functions $H, S, G$. I have searched a lot in textbooks but they don't give the complete information as to whether the properties taken are that of the system or surroundings.

Q1):-Enthalpy is given by the formula

$H = U +PV$ .
 What I want to know is that whether $P$ mentioned above is the internal pressure of the system or the externally applied pressure?

Q2):- The change in entropy is given by the formula
$\Delta S= $$\int_1^2$${\frac{dq_{reversible}}{T}}$. Is the temperature mentioned of the system or the surroundings.

Q3)-On the same lines what temperature is taken to define the Gibbs free energy function:-$G=H-TS$.

Thanks in advance.


texts: Question about liquid-phase in P-T Diagram

texts:
Currently, I have been learning about P-T diagrams and vapour pressure and I have a question that seems like it should have a simple explanation yet I am not able to understand it.

Taking the P-T diagram of water for example,

Suppose we choose a point that corresponds to the liquid region in the P-T diagram. From what I know of vapour pressure, every pure liquid in a closed container has a vapour pressure and will eventually reach a liquid-vapour equilibrium. If this is the case, what is the meaning of a "liquid region" in a P-T diagram if there must always exist a vapour-liquid equilibrium? And by extension why is there even a coexistence curve between liquid and vapour in the first place?


texts: Placing of lone pairs in axial/equatorial position

texts: If the lone pairs of elections are put on axial or equatorial position such as to minimize the intera-electronic repulsion, and for the same reason in $\ce{SF4}$, the election pair is kept on the equatorial position(at 90 degrees to only two domains), why then in $\ce{BrF5}$ the lone pair is kept on the axial position, when it is at 90 degrees with 4 domains?


texts:
I am learning about structure of atom, in which i saw right from J.J. Thomsom atomic model to modern nuclear atomic model all are spherical in shape.

I have seen how different discoveries help to develop the atomic model but i have't came through a single discovery which proves that atoms are spherical in shape.

So, Why atoms are spherical in shape?


texts: Why are moles used in the ideal gas law and not simply mass?

texts:
The crux of my question is, why is just the amount of particles included in $PV=nRT$ and there is nothing to account for the mass of the individual molecules? Or is mass accounted for in temperature, the average kinetic energy which includes mass in $\tfrac{1}{2}mv^2$.

Thanks in advance!


texts:
What is an alloy called when it melts at the same temperature as something else? For example, if there is an alloy that melts at the same temperature as glass then it will be susceptible to enameling and it is called an XXX-alloy.

As I recall, the term begins with the letters "eu-".


texts: Introduction to Chemistry Textbook - Theory based

texts:
TL:DR conditions below

Highschool to first year undergraduate level
Theory based(Experimentation not wanted)
General - Giving a good introduction to all or most areas of Chemistry
Rigorous - Professional formatting - Not a casual textbook

I am looking for a textbook for someone(me) who has done no chemistry, but isn't too basic as it progresses. What are some of the better textbooks for starting to learn chemistry? I don't know any specific fields, so I would like to get some exposure to a number of different topics. I am a third year Mathematics student, so I am not worried about it being too concise, I am willing to reread areas one hundred times if need be.

One note: I am not interested in doing experimentation at all, and would just like to learn theory, as I have (sometimes) embarrassingly bad knowledge of the field as I didn't take chemistry in highschool(which I greatly regret).

Highschool through to the end of first year undergraduate level preferably, or alternatively multiple textbooks by the same author of successive difficulty.


texts:
Are $\ce{CH2=CH-CH=O}$ and $\ce{CH2=C=CH-O-H}$ tautomers?

There is only a shift of a hydrogen atom and a pi bond. So why are these two not tautomers?


texts:
Can anyone help me with a quick question regarding MestReNova 9.0. I have been fiddling with this thing all day and before you ask yes, I have consulted the users guide to no avail.

I want to do three things:

1)Rescale the chemical shift axis to focus only on the relevant sections of my spectra.

2)Set a threshold so that only peaks above a certain intensity will automatically label.

3)how on earth do you get the parameter box to fit onto the page? Ive managed to get it up but it is about three times larger than my spectra and rescaling using the little green buttons leaves it the same size but just cuts loads out.

Any help is much appreciated!


texts: What gases would be produced from the electrolysis of distilled water and sodium bicarbonate?

texts:
I have two questions: one practical question and one conceptual question.

1) I'm trying to set up an electrolysis experiment and I am trying to make sure I am going to end up with the gases that I think I will. I am planning on using stainless steel electrodes, and sodium bicarbonate (baking soda) as the salt, dissolved in distilled water. I am not using NaCl, as I believe it would produce some chlorine gas as well.My thought is that using sodium bicarbonate, I would get hydrogen and oxygen gas, but I am unsure if it would produce some CO2 as well...

Basically I am not sure what the intermediate reactions are, and I am not sure how the baking soda breaks up and what you are left with. I am trying to produce hydrogen and oxygen gas, and I want the 2 to 1 ratio, so I want to make sure I am not getting other gases as well (I don't care so much about any solids produced, so long as they are not dangerous.

2) Also a side question that I have been wondering about: I have been looking at different electrolysis experiments online, and I have found two different types. From what I understand, one type uses two electrodes that are separated from each other, and the current is allowed to pass through the solution, which conducts electricity due to the ions and breaks up the water molecules into hydrogen and oxygen. The second type I have found is composed of multiple plates to increase surface area.
 (https://drive.google.com/file/d/0BzXcmrdDUUGNOFc2cUJldnBJRnc/view)

From what I understand, they are spaced so that they alternate between positive and negative, though I saw some that use neutral plates (not sure what those are for). I believe hydrogen and oxygen bubbles are then formed on the surface of the metal. What is really happening in each setup (where are the bubbles being formed...) and are they really different at all, or is it just about the size of the gap? And what is the purpose of the neutral plates?

Thanks so much for your help!
-Abe


texts: Why isn't neptunium used in nuclear reactors in nuclear power plants?  Uranium is, and plutonium is. But neptunium isn't and it is in the middle of them.  Is it like it is too hard to make it do fission?  Can someone please kindly explain it to me?


texts: Is ozone an electrophile in the ozonolysis reaction?

texts: From the above mechanism it is clear to see that the electrons from the double bond attack one of the terminal oxygens in ozone, thus meaning it's an electrophile. How can this be? If you draw the resonance structures, the negative charge is concentrated on the terminal oxygens too. I am OK with the rest of the mechanism but I would never think to draw oxygen as an electrophile.


texts: Why isn't iron(III) oxide an effective catalyst for decomposing hydrogen peroxide?

texts:
I've been working on a project involving the catalyst iron(III) oxide for decomposing hydrogen peroxide.
It barely seemed to produce any oxygen.

This YouTube video also seems to suggest that iron(III) oxide isn't a very effective catalyst.
But why?


texts: Software for modelling decomposition reactions

texts:
What are some good softwares that can model a decomposition reactions?
I have a reaction of H2O2 decomposing on metal exchange hexaaluminate catalyst. The catalyst is present in a packed bed thruster. I have done the micro-kinetic modelling of the diffusion and reaction that might be happening on the catalyst on paper.
I need a software that can model the mass transfer and other transport phenomena that might be happening inside the thruster. Also are there some other softwares that can model the surface reaction and the adsorption/desorption steps that be happening on the surface of the catalyst.
I have the following data that could serve as the input to the software-

Experimental rates (average rate and instantaneous rate)
Some assumptions of the kinetic rate and equilibrium constants derived using non linear regression and least sum of squares method
All physical dimensions of the thruster bed and the catalyst pellets.

Any suggestions will be welcomed. I work mainly on the experimental chemistry side ,and this is the first time I will be working on the computational side.
P.S please ignore grammatical errors (english is not my first language)


texts:
I'm doing revision questions and want to double check something. The opening information reads:

  Two chlorides of iron were prepared. One was prepared by reacting iron with dry chlorine
  gas. 4.50 g of iron reacted with chlorine gas to produce 13.01 g of the chloride.
  The other chloride was prepared by reacting iron with dry hydrogen chloride; 2.80 g of iron reacted with hydrogen chloride to produce 6.35 g of the chloride.

The questions are then:

  (i) Calculate the mass of iron that reacted with 2.80 g of iron in each chloride.
  (ii) Find the ratio of the different masses of chlorine that combined with 2.80 g of iron.
  (iii) Which of the chemical combination laws is demonstrated using this data?

Is that first question right? I would've thought they're asking to calculate the mass of chlorine, which you'd simply get by subtracting the mass of reactant iron from the mass of the end product.


texts: In infrared spectroscopy, why is there no C=C reading for E alkenes?

texts: For the (E)-2-pentene, there was no C=C reading, about 1600. For the (Z)-2-pentene, there is a C=C. Why is there a reading on the Z but not on the E?


texts:
I've recently just started learning about Chemistry, and more specifically, Ions.

In class, we learned about how Valence Electrons are electrons located in the outer-most orbitals and how every atom (with the exception of Hydrogen and Helium), want $8$ valence electrons.

When possible, an atom will attempt to get rid, or add, an electron to get $8$ on its outermost shells. For example, Sodium and Chlorine.

We learned that it's easier for Sodium ($\ce{Na}$) to lose an electron to get the $8$ outer electrons it always wanted, and for Chlorine to receive that $1$ refuted electron. Then, they form an Ionic bond and you get Table salt!

But now, I'm wondering: what if that's not possible? What if you have an element such as Beryllium and Lithium? Would they simply not combine? Or would something else happen? I am confused.


texts: Why is quickly cooling a a hot pan bad for it?

texts:
I've heard that really quickly cooling a hot pan is bad and reduces the lifetime of the pan. I'm wondering, from a chemical perspective, why this would be true. My thought is that as a pan is heated up, there may be slight rearrangements in the lattice of the metal, which, if allowed to cool, would likely reset into the correct portion of the lattice. On the other hand, if quickly cooled, perhaps these atoms don't make it back into the correct place, and this warps the pan.

As a secondary question to this idea of warping a pan, why would reheating the pan not cause it to return to the original shape? Seemingly, that original shape is a lower energy structure of the lattice, so with enough energy to overcome barriers, why would it not "unwarp"?


texts: How pure NaCl is typical table salt? How is it purified?

texts: How pure $\ce{NaCl}$ is typical table salt? Is it pure enough for research-level experiments in chemistry? How is $\ce{NaCl}$ purified if need to be?


texts:
My Momma bought a copper pan made for induction because it was the only one she could find that she wanted and was big enough to pan fry half a chicken.

But I noticed something odd about the copper. It seems to be magnetized. I thought that was impossible because copper is paramagnetic, not ferromagnetic. How is that possible that a paramagnetic material could be magnetized and remain magnetic even when a magnet is nowhere near it? Is it possible that they purposely put tiny amounts of iron in the copper to magnetize it and let it retain its magnetism kind of like how neodymium magnets aren't pure neodymium?


texts:
I want to determine rate of Fenton reaction with different concentration of $\ce{Fe^2+}$. These are some questions that I have encountered:

How long does it usually take for the reaction to complete?

What concentration of $\ce{Fe^2+}$ is usually used for the reaction?

I am planning to use titration of $\ce{H2O2}$ with $\ce{KMnO4}$ to determine the rate of reaction. Is it possible to quench to reaction mixture by adding an excess of EDTA solution and would it affect the titration?

NEW:
How can I determine the rate of Fenton reaction? I proposed to titrate $\ce{H2O2}$ with $\ce{KMnO4}$ to determine change in $\ce{H2O2}$ as a mean of determining rate of reaction. However, I realised that $\ce{KMnO4}$ would also react with $\ce{Fe2+}$, so I need to either find another way to measure the reaction rate or find a way to remove all $\ce{Fe2+}$. Also, I am not sure if there would be any reaction between $\ce{KMnO4}$ and the hydroxyl radicals.
I am also wondering about adding in some wastewater and determine the before and after COD to determine the rate of reaction. However, I am wondering if the water that don't really have high COD (as opposed to the industrial wastes used in other papers) would result in a very slow reaction rate. Also, it seems like the part involving oxidizing by hydroxyl radicals is very exothermic. If I don't want to add $\ce{H2O2}$ bit by bit to control rate of reaction, is it OK?
Do I have to add acid to $\ce{Fe2+}$ and $\ce{H2O2}$ for the reaction to occur?
Is it necessary to add $\ce{H2O2}$ bit by bit, if so how much should I add at each turn?


texts:
A full FAQ exists on meta.chem.SE explaining the premise of synthesis golf, why we're doing this, and the ground rules. Please read this before posting an answer.

The target for this first round of synthesis golf is sodium fluvastatin, an artificial statin drug used to treat hypercholesterolemia and in the prevention of cardiovascular disease. You must provide a synthetic route to the target molecule.

In addition, to narrow the scope of this question:

the synthesis must include a way of making the indole (i.e. no buying of the indole core and carrying out multiple functionalisation reactions).
all of the stereo centres must be set. Relative stereochemistry only is fine (the 1,3-syn relationship between the hydroxyls), but if you can think of a way to set them with absolute configuration, then great.


texts: Why does cobalt(II) chloride (CoCl2) crystal melts?

texts:
I made $\ce{CoCl2}$ crystals by making a concentrated solution. After the crystals formed I took them out of the solution for drying.
 After a time I noticed that they were still wet so I dried off the water with a cloth and left them. Again they got wet and it seemed that the crystals just melted enough to get wet. No matter how many times I wipe them they again get wet.
Currently I am keeping them in an airtight container inside refrigerator.

So why does it happen and is there a way to preserve $\ce{CoCl2}$ crystals?

My explanation: I think that it is possible that $\ce{CoCl2}$ crystals that I made exist as $\ce{CoCl2.2H2O}$ (which is purple, as are my crystals) and it reacts with humidity to form $\ce{CoCl2.6H2O}$ (pink in color, as was the wet melted crystal)
Though I may be wrong.


texts: Closed shell molecules can have degenerate states?

texts: I read a paper which said that $\ce{CO2}$ despite having orbital degeneracy is stable and not subject to the Jahn-Teller effect because it is a linear molecule. But $\ce{CO2}$ is a closed shell molecule, so how can it have orbital degeneracy?


texts: How to choose the best method and basis set for a calculation in computational chemistry?

texts:
In Quantum chemical calculations, it is not always the case that the more complex (correlated) the method or the basis set the more accurate the results.

For example, it's sometimes found that MP2 results better fit the experimental results than that of CI calculation.

In other instances diffuse functions negatively impacts the accuracy of the calculation.

Are there any general rules for the choice of a method and the basis sets?

What is the degree of accuracy of a calculation with no experimental reference ?


texts: Sulfonyl azides: diazo or azide transfer?

texts:
Sulfonyl azides, $\ce{RSO2N3}$, are capable of acting as sources of electrophilic azide ("$\ce{N+3}$"), but are also capable of effecting diazo transfer, as shown in the scheme below, taken from ref 1:

In 1990, Evans and coworkers1 showed that the aryl group on the reagent was important in controlling the outcome of the reaction:

$$\begin{array}{ccc}
\ce{Ar} & \text{yield of }\textbf{3a-S}\text{ / %} & \text{yield of }\textbf{5a}\text{ / %} \\ \hline
\ce{(4-NO2)C6H4} & 15 & 70 \\
\ce{(4-Me)C6H4} & 51 & 26 \\
\ce{(2,4,6-^iPr3)C6H2} & 91 & 0 \\
\end{array}$$

which suggests that $\ce{TrisN3}$ (the third entry) is the best azide transfer reagent.

However, confusingly, it has also been reported that under phase transfer conditions, $\ce{TrisN3}$ outperforms $\ce{TsN3}$ (the second entry) in diazo transfer to ketones.2

With this in mind, Evans concluded that

  Collectively, these independent observations underscore the lack of mechanistic sophistication which currently surrounds these reactions.

Since then, have there been any efforts to rationalise the effect of the aryl group on the product distribution? And if so, how can the results above be explained?

References

Evans, D. A.; Britton, T. C.; Ellman, J. A.; Dorow, R. L. The asymmetric synthesis of α-amino acids. Electrophilic azidation of chiral imide enolates, a practical approach to the synthesis of (R)- and (S)-α-azido carboxylic acids. J. Am. Chem. Soc. 1990, 112 (10), 4011–4030. DOI: 10.1021/ja00166a045. Non-paywall version available from the Evans group website.
Lombardo, L.; Mander, L. N. A One-Step Synthesis of Cyclic α-Diazoketones. Synthesis 1980, Vol. 5, 368–369. DOI: 10.1055/s-1980-29022.


texts: How to find the Cp, difference of Cp and heat of fusion from the dependence of vapor pressure on temperature?

texts:
The vapor pressure of zinc varies with temperature as
$$\log P(\pu{mm Hg}) = -6850/T - 0.755\log T + 11.24 \label{eqn:1}\tag{1}$$
and that of liquid zinc as
$$\log P(\pu{mm Hg}) = -6620/T - 1.255\log T + 12.34 \label{eqn:2}\tag{2}$$
Calculate:
a) boiling point of $\ce{Zn};$
b) triple point;
c) heat of evaporation at boiling point;
d) heat of fusion;
e) the difference in $C_p$ of solid and liquid zinc.

I have found out the boiling point by substituting pressure as $\pu{760 mm Hg}$ on first equation \eqref{eqn:1}, from here boiling point $T$ can be found out as $\pu{1181 K}.$
I have also found out triple point by equating the two equations because at triple point both the pressure of the two phases must be equal.
I have also found out heat of vaporization by using the equation
$$\frac{\mathrm d\ln p}{\mathrm dT} = \frac{H_\mathrm{vap}}{RT^2}.$$
But to find the heat of fusion I must know the heat of sublimation, but the heat of sublimation is not provided here. Is there any other way to know the heat of fusion (melting)?
Also, how to find the $C_p$ of both the phases and the difference of $C_p?$


texts: The sign of enthalpy of formation of magnesium oxide

texts:
I'm currently doing a lab to calculate the enthalpy of formation for $\ce{MgO}$. However at the moment me and my lab partner are having a disagreement. We've both calculated and agreed upon the same heat released in the reactions ($\pu{4.2\frac {kJ}{mol}}$ (reaction of $\ce{MgO +2HCl})$ and $\pu{7.5\frac {kJ}{mol}}$ (reaction of $\ce{Mg +2HCl}$)). Where we disagree is over how to calculate the enthalpy of reaction.

My argument:

Enthalpy is the amount of energy put into the reaction, what we measured is the heat released thus the equation should be:
$$\Delta H=-\frac{Q}{n}$$
Also, this would make sense considering our reactions were blatantly exothermic, and using this equation provides negative values.

Her argument:

The equation is simple and the teacher agreed with her results:
$$\Delta H=\frac{Q}{n}$$

My question: Who is correct?


texts: The explanation I have found is that primary cells have irreversible reactions, so passing current in the opposite direction cannot recharge the cell. But as far as I understood it, no reaction is really irreversible - what one calls irreversible simply has very high values of the equilibrium constant, so for all intents and purposes proceeds to completion. Nevertheless, some small - maybe undetectable practically - amount of reactant does remain and the reaction does reach equilibrium. So even in a primary cell, when it is used up, equilibrium has been achieved, so recharging should be possible - it might take long to build up the initial value of potential since the required concentration of the electrolytes will be very different from that at equilibrium, but it should be possible. Why then is it not?


texts: What question could be answered by "because the metabolites in the cell are in ionized form" in the topic of anaerobic metabolism?

texts:
I know it might sound a bit absurd, but my teacher gave us some "answers to question", that is, given one answer, write at least one question the answer to which is the given one.

I've solved most of the answers, but there's one I just can't figure out: "because the metabolites in the cell are in ionized form", and the topic is anaerobic respiration and fermentation. No additional details from her.

I'm in high school (a "scientific" school in Italy), if that can help for the knowledge level.

Any idea?


texts: Mechanism for reaction of NOCl (Tilden reagent) with primary amines

texts:
According to my textbook, the reaction between $\ce{NOCl}$ and $\ce{CH3CH2-NH2}$ is as follows:

  $$\ce{CH3CH2-NH2 + NOCl -> CH3CH2Cl + N2 + H2O}$$

But how exactly does the reaction proceed?

The first step (what I think) could be that $\ce{NOCl}$ dissociates into $\ce{NO+}$ and $\ce{Cl-}$ ions and then the $\ce{Cl-}$ ion attacks the amine group and replaces it by $\mathrm{S_N2}$ mechanism.

But according to this site, a diazonium product is produced. Even though a diazo product is formed, how does it produce an alkyl halide according to my textbook?


texts:
Why is $\ce{HClO4}$ the strongest oxyacid?

My effort: The structure of $\ce{HClO4}$ should be tetrahedral. So when there is a negative charge on oxygen, it should not be in resonance with other oxygen atoms as a condition for resonance is that the atoms taking part in resonance should lie in a plane.


texts:
We have a laser chamber full of $\ce{F2}$ gas (no air should be in the chamber) and several parts including steel, wires, ceramics, zinc.... This is for laser generation so the temperature is pretty high in the chamber. We have detected $\ce{NO2}$ gas in our FTIR specturm which caused our laser to fail and there’s a good chance that the $\ce{NO2}$ may be associated with the failure. The questions are

How might $\ce{NO2}$ be formed in a chamber? If it’s from air, why would $\ce{NO2}$ be formed and not $\ce{NO}$ or $\ce{N2O}$? Why would $\ce{NO2}$ persist after $\ce{N2}$ and $\ce{O2}$ are removed by chamber refills with fresh $\ce{F2}$?
How does $\ce{NO2}$ interact with fluorine? What other species might be formed when they react?
Can $\ce{NO2}$ be dissociated by UV light (i.e. 193 nm)? What is its UV absorption spectrum?


texts: What happens if the electronegativity difference is exactly 2.1?

texts: I'm learning about electronegativity in atoms and how their difference affects the type of bond they make. I know that no difference makes a non-polar covalent bond, a difference less than 2.1 is a polar covalent bond, and a difference above 2.1 is an ionic bond. But what kind of bond forms if the difference is exactly 2.1?


texts:
Why is the density of cyclic hydrocarbons more than that of their acyclic counterparts?

For ex:

Cyclopentane: 751 kg/m³
Pentane: 626 kg/m³

Cyclohexane:779 kg/m³
Hexane:655 kg/m³

In fact, as you can see above, cyclopentane is even denser than hexane.

My reasoning so far is:

Attractions in hydrocarbons depend only on London forces, which increases with surface area.
An alkane will have more surface area for bonding as compared to a cycloalkane (The inside of the ring cant be used), so it will have more forces, and hence will be packed closer (be denser).

But this contradicts the facts.


texts: What is the electronic structure of Mn in KMnO4 and K2MnO4?

texts: I know that is is d3s hybrid. But in my book it is unclear which orbitals participate in pi bond with O. I think it should be both p and d orbitals of Mn that do.


texts: Rationalizing Acidities of Ammonium Ion and Hydronium Ion

texts:
Stumbled across this interesting practice problem in my organic textbook. I have a few reasons for why $\ce{H4N+}$ is less acidic than $\ce{H3O+}$.

1) Let’s assess conjugate stability first. Conjugates are $\ce{H3N}$ and $\ce{H2O}$. Let’s look at central atom oxidation state. Nitrogen in ammonia has an oxidation state of negative 3. Oxygen in water has an oxidation state of negative 2. The more negative oxidation state of nitrogen suggests it is more nucleophilic than oxygen (i.e. more reactive). The more stable the conjugate base, the stronger the acid. Water appears to be more stable through oxidation state analysis.

2) Oxygen is more electronegative than nitrogen, so there is more electron withdrawal from the hydrogens in the hydronium ion. This gives the hydrogens in hydronium ion a higher partial positive charge, making them more electrophilic (and hence more reactive). This is the reason (the sole reason) my book offered.

3) Size plays a role in the direct acidities of the two molecules. First, nitrogen is bigger than oxygen. Both hydronium and ammonium ion have a positive 1 formal charge. The bigger size of nitrogen decreases its positive charge density, making it less Coulombically favorable for ammonium ion to kick off a proton.

Are these reasons 1) valid and 2) are there any more reasons I may have overlooked?