texts: Is there s-character in the HOMO of dinitrogen?

texts:
State true or false:
The highest occupied molecular orbital in nitrogen molecule has no s-character.

The answer given is that this false. Why is it so?
The highest occupied molecular orbital in $\ce{N2}$ is the sigma $2\mathrm p_z$ orbital. So it should not have any $\mathrm s$ character and hence the statement should be true.


texts: How can we predict the colour of transition metal complexes?

texts: I am facing problems in indentifying colour of complex compunds just by seeing the their molecular formula. Is there any method or concept to predict the colour of complex compunds?


texts: Entropy and Heat Capacity Trend in water

texts: It is my understanding that entropy and heat capacity essentially measure the same thing. Since entropy is the ratio of heat (translational, rotational, vibrational movement) to temperature (translational movement), a substance with higher entropy (heat/temperature ratio) would require more heat to raise a certain temperature, which is the definition of heat capacity. Why then, is the heat capacity of liquid water around 4.2 J/g-K while for water vapor, it's only 2.0 J/g-K when vapor has more entropy?


texts: For a system containing three reductants, can a combined reduction potential be determined?

texts:
I've modelled a system and found that there are three major complexes present at equilibrium, all of which I hope will act as reductants when I add an additional, oxidised species. Each of the three complexes has a different concentration in the solution, and each has an associated reduction potential.

Is there any way to find an overall reduction potential for my reactor, based on some combination of reduction potentials?

I could be missing something fundamental!


texts: How do equilibrium shifts affect solids?

texts:
Say we have the following reversible reaction: $$\ce{NaOH{(s) }<=> Na^+{(aq) }$+ $OH^{-}{(aq)}} +10.6 \mathrm{kcal}$$

If we add $\ce{OH^-}$ and equilibrium shifts to the left, does that affect the amount of $\ce{NaOH{(s)}}$ present or does it remain constant?

I'm confused because I remember that pure solids and liquids don't affect equilibrium value, or does that only apply when we're talking about adding pure solids and liquids..not the effect on them by an equilibrium shift?


texts: How does soap actually reduce surface tension of water

texts:
I was a bit confused on how soap reduce surface tension of water.I've read some answers like Why does soap reduce surface tension of water and Why do surfactants lower the surface tension
But the answers given don't clears my doubt that if the soap molecules come to the surface to separate the water molecules and weaken the hydrogen bond, wouldn't they form stronger ion dipole interactions and increase the surface tension.I mean they would attract the water molecules with greater force.
I do understand from the energy point of view but I wanted to understand it considering the forces.
I know that it is a repeated question but consider giving an explanation to my point.


texts:
How good of a thermal insulator is superglue compared to other materials like ceramics, plastics, and metals?

I know this might not seem like a chemistry question, but I was hoping someone here could provide a more meaningful answer than what I found online, which was basically along the lines of, "It's not a good heat conductor so don't use it in cooling applications." I was hoping for a little more substance than that, so that's why I wanted to ask it on here.

Ideally, I would love for the answer to include one of the following things:

An approximate numeric comparison between superglue (liquid or gel) and other materials (for example plastics, metals, and ceramics).
Or a qualitative answer, like the example I gave above, but with a short explanation based on the chemical characteristics.
Or perhaps a chart of thermal conductivities of various superglues relative to other common materials.

If a similar question already exists -- or there is a free resource available online that can answer it -- then a link with a short explanation would be a perfectly good answer as well.

EDIT 1:

I know it sounds like I'm asking for a very big answer, but the suggested answers above were just suggestions. Really, the most important thing (for me at least) is to get a feel for where superglue falls in relation to other common materials.

EDIT 2:

In response to Greg's comment: I would have liked to share my finding on the subject, but unfortunately I have not been able to locate any formal research on the matter. The best I was able to find so far were forums and blog articles, which were usually either vague or offered little-to-no supporting evidence of their answers. Perhaps I just don't know the right places to look for information like this, and if this really is the case then I hope you all can give me some direction as to where I can find some research on this matter.


texts:
I'm trying to do a thermite reaction with rust and aluminum and am trying to figure out the optimal way to get the reaction started. My understanding is that I need a temperature of around $\pu{3200 ^\circ F}$ to start it. I am currently aware of two methods to achieve that:

Potassium permanganate and glycerin: But apparently this requires an ambient temperature of $\gt \pu{70 ^\circ F}$, and it's winter where I live, $\pu{40 ^\circ F}$ at most some days.
Magnesium strip: But this requires a blowtorch (trying to avoid buying a blowtorch) and I've read is unreliable for starting this reaction.

Does anyone have any alternative suggestions? Has anyone done this before? All suggestions are welcome.
I am aware of the need to do it far from anything flammable/destructible, and am aware it can damage your eyes, and am aware to keep it away from water and keep my distance. Other tips are welcome.


texts: Difference between Henry constant and equilibrium constant

texts:
According to wikipedia, Henry constants define the ratio between the aqueous and gas fraction of a chemical species at equilibrium.
Lets consider Henry constants H in atm.L.mol-1 such that $[C]_{g} = H \cdot [C]_{aq}$.

Based on this definition, H is actually the same thing as the equilibrium constant K of the dissolution equation of the chemical species of interest. Indeed, using Gibbs energies found on this site, K provides a good approximation for H in the case of CO2 for example ($\Delta G^0$ of the reaction is -8.4 kJ.mol-1, and $K = e^{-\frac{\Delta G^0}{RT}}$ gives 29.62 atm.mol-1, very close to the value found in Sanders 2015).

However K computed this way is not always close to H (for example in the case of $H_2$ where it is 1211 atm.mol-1 while H is reported as 1300 atm.mol-1). What is then different between using Henry constants and equilibrium constants to compute the saturation concentration of a chemical species?


texts: From previous lessons, I know that column 1 are alkali metals, column 2 are alkaline earth metals, column 3 till column 12 are transition metals, column 17 are halogens and column 18 are inert gases. But till now I don't know the properties of elements in columns 13, 14, 15 and 16... Are they metals or non-metals? I have not faced such a question before.


texts: Getting close to zero percent of particles with energy greater than an activation energy of 101kJ/mol using the Maxwell-Boltzmann energy distribution

texts:
I experimentally obtained the activation energy of a reaction to be approximately 101kJ/mol. I was then going to use the value for the activation energy to see how the number of particles with sufficient energy to undergo a successful reaction changes with temperature using the Maxwell-Boltzmann energy distribution. However, I noticed that the graph already approaches zero close to 10kJ/mol. I attached a photo of the equation and graph.

Am I doing something wrong?
I am certain that the activation energy of the reaction I am studying is around 100kJ/mol and that a reaction really does occur.
Another question, what does the y-axis really represent?
I graphed the proportion of particles with sufficient activation energy vs. temperature in Kelvin and I found that it increase exponentially. So exponentially that it seems almost vertical. Here is a picture of it. I could also have made a mistake though.


texts: Cis Orientation of dienophiles orientation of groups maintained in Diels Alder

texts:
When I was reading about Diels-Alder reactions, I was confused about the cis and trans rules for dienophiles, as shown below.

The text told me that "a cis dienophile will generate a ring with cis substitution, and trans dienophiles will generate a ring with trans substitution."

I'm a bit confused.

Why is this the case?


texts: What happens to a flat lemon and can it be recharged?

texts:
A lemon can be used as a battery, and is often used to teach kids the basics about electricity and chemistry.
This is due to their acidic and electrolytic properties.

What happens to a lemon when it goes flat, does it drain like an ordinary battery?
Once the lemon is flat, can it be recharged like a rechargeable battery?
How does this affect the lemons decomposition?


texts: What can explain the more weight gain of aluminum coated steel than non-coated steel after NaCl immersion?

texts: I have a 2 week experiment. I put aluminum coated and non-coated steel of the same size and shape in separate beakers with NaCl solution. Both are sealed. But, I am surprised that Al coated steel gained more weight than the non-coated steel after immersion. I know that the weight gain can be attributed to the formation of corrosion products. The measurements shows that the coated steel gained more weight, which be indicates more corrosion. But I'm sure that it doesn't since the liquid solution is still clear without any sign of rust. Unlike on the non-coated steel which has formation of rust that settles at the bottom.


texts: Dissolution of Pentahydrate of Copper Sulfate

texts:
I'm having some difficulty understanding how the pentahydrate of copper sulfate dissolves in water.  I understand how polar molecules work, and how things dissolve in water, but I can't get my head around this in particular.

What happens to the water molecules in the pentahydrate?  Does the copper sulfate split up at all?  What makes the solution blue, if the solute is split?


texts: Why does water condense on grass and iron grills in cold weather?

texts:
In my book it is said that in cold weather fog appears. This fog is nothing but water droplets. After a hot day if the night is cold then the moister in air starts to condense. What I do not understand is why does water condenses heavily on specific places like grass and iron objects only? I first thought that since iron is good conductor of heat so it becomes cold at night early which then captures nearby moisture more effectively than usual objects. But then grass is a poor conductor of heat. Another thought is that most of the objects absorb water. Those which do not absorb are metals and grass.

Please explain.


texts: What's the meaning of the $-\equiv-$-like bond symbol?

texts: In the following image, $\mathrm{CH}_2$ is connected to benzene rings with a $-\equiv-$ like symbol. What's the meaning of this symbol?


texts: Why does ammonia accept a hydrogen to form ammonium when its octet is already complete?

texts: Why does ammonia accept a hydrogen to form ammonium when its octet is already complete as $\ce{NH3}$ and it should be, seemingly, stable as $\ce{NH3}$?


texts: Comparing the number of oxidation states of Vanadium and Arsenic

texts:
USNCO 2004 Question 45 states:

  Which element exhibits the greatest number of oxidation
  states in its compounds?

  (A) Ca (B) V (C) Cu (D) As

I ruled out Ca, as I know it only exists as +2. I then drew electron configurations for V, Cu and As. I ruled out Cu as it had half filled 4s and full 3d orbitals, also because I've only ever seen copper in a +2 oxidation state.

However, I wasn't able to differentiate between V and As. They both have 3 unpaired electrons, albeit As has an extra full 3d orbital.

I was tempted to go with As, as being less metallic than V, it is more likely to have negative oxidation states, but the answer states Vanadium has the most oxidation states.

Is there any way I can work this question out by looking at electron configurations, or will I have to memorize the oxidation states?


texts: Can I mix pressures and concentrations when finding equilibrium constant?

texts:
In order to find the equilibrium constant (or reaction quotient) I know I can find the value as the products over reactants raised to coefficient exponents. But, in all of the problems I have had to date, I have had either concentrations of solutions or pressures of gases. Now I have a problem with both. Can I mix the two?
Here is the chemical reaction:
$\ce{2 Al (s) + 6 H+ (aq) -> 2 Al3+ (aq) + 3 H2 (g)}$
I am told that the concentrations of the aqueous solutions are $\ce{[Al3+] = 9.3701}$ M; $\ce{[H+] = 4.6}$ M; and hydrogen pressure is 0.0271 atm.
If I can "mix" concentrations and pressures, then my $K_{eq}$ or (Q) is:
$Q = \frac{9.3701^2 * 0.0271^3}{4.6^6}$
$Q \approx 1.84 E{-7}$
If I can't mix them then I need to do some kind of conversion between concentration and pressure. I'm not sure how to do that. A conversion might be based on $K_p = K_c(RT)^{\Delta n}$ but I don't have enough information to make a conversion using that formula.
So, the bottom line, can I mix concentrations and pressures and, if not, how do I make a conversion from one to the other?


texts: Determination of carbon dioxide according to EN 196-2

texts:
I struggle with determination of carbon dioxide according to EN 196-2.
First of all, I have a problem with absorption tubes' mass not stabilizing. I've tried changing absorbent, washing tube thoroughly with distilled water and acetone, and using another tube - but it won't help and tube's mass is constantly descreasing by about 0,005g per 10 minutes.
Another problem is that much less carbon dioxide is being absorbed in absorption tubes than it should, basing on results of loss on ignition. I'm using Carbosorb. I've tried to seal the system as much as I can with parafilm and insulating tape, replace sulfuric acid in wash bottle and replace absorbent in tubes very often. Nothing seems to work. Please help!
EDIT: some context regarding EN 196-2. Sample is placed in distillation flask and phosphoric acid is added to decompose carbonate. Flask is heated for 5 minutes after adding the acid. Created CO2 is carried with carrier gas through a condenser, wash bottle with sulfuric acid and then through a series of absorption tubes. The first two remove hydrogen sulfide and water. Third and fourth tube are filled with CO2 absorbent and anhydrous magnesium perchlorate. CO2 should be absorbed on these two tubes and then tubes are weighed to determine the mass of released CO2. Before phosphoric acid is added, tubes should be flushed with gas until their mass is constant - they are weighed every 10 minutes and change in their mass shouldn't be greater than 0,0005g.


texts: EPR spectrum of a singlet-triplet mixture

texts:
Through EPR measurements it is possible to gain information about the spin states of molecules. So a singlet state will give no signal/only noise and a molecule with unpaired electrons will result in an EPR spectrum.

What happens if a measured sample would contain a mixture of singlet and triplet state molecules (of the same species)? Will there be a signal for the triplet state or is there any interaction between both that hinders the experimentalist from measuring the triplet states?


texts: Substitution reactions haloalkanes confusion

texts:
"In haloalkanes, the large electronegativity difference between halogen and carbon atoms means that the carbon-halogen bond is polar. This makes the bond weaker than one without a dipole" - excerpt from my textbook
I don't particularly understand the last sentence. Can someone elaborate and explain what does "this makes the bond weaker than one without a dipole" means?
the strength of the inter molecular force goes the following: Dispersion, Dipole–Dipole and Hydrogen Bonding.
From my interpretation: Without dipole is equivalent to dispersion and dispersion is subsequently weaker than dipole dipole. But why does dipole dipole weaker than one without a dipole? Shouldn't it be stronger?
That sentence continues with "Species such as another halogen ion, a cyanide ion, ammonia can be substituted for the halogen in the polar bond."
Any help will be great. Thanks.


texts: How is volatility useful in the production of acids?

texts:
Sulfuric acid because of its low volatility can be used to manufacture more volatile acids from their corresponding salts.

How does volatility affect the production of acids? Isn't it that sulfuric acid being stronger than the salt of weak acid replaces the anion part of salt so the weak acid is produced or does just the low volatility of sulfuric acid matter? Will it be feasible to produce a highly volatile acid even stronger than $\ce{H2SO4}$ by exploiting the low volatile nature of $\ce{H2SO4}$?  What is the real process involved?


texts: Question about the setting of DFT (Density Function Theory)-NEB (Nudged Elastic Band) calculation

texts:
I'm attempting to calculate Mg ion vacancy migration inside Pyrope unit cell. System has total 159 atoms, beginning and end geometry is optimized. For intermediate image, I'm using one coordinate that I acquired from crashed NEB case. This is not perfect intermediate geometry, but I thought this should be enough one to guide NEB.

1) Is there any rule of thumb to decide "num_of_images" based on moving distance of target atom?
In my script, I wish to move one Mg atom from one position to next vacancy which is about 3.5 angstrom away. In this case, how many images for NEB would proper? For example, if I choose 1 image per 0.5 angstrom, then 8 images should be chosen including the beginning and the end. But I'm not sure if 1 image per 0.5 angstrom would be the proper value. How do you decide "number of images" per given distance?

2) How many core number should be chosen for NEB?
I have some sense of core number decision based on my experience, but this is for relaxation. For NEB, I'm not sure how much core number is proper for given atom number or given number of images setting. I wish to learn if there are rule of thumb to decide core number for given NEB conditions.

3) How to decide intermediate image?
First, I tried my best guess of Mg ion location between two vacancies as an intermediate image. Then, I'm using one from one of the crashed NEB simulation result. Is this good approach?

4) Can freezing atom helps convergence? (freezing = fixing x, y, z coordinate of atom)
Is this better to freeze (put 1 1 1 beside the atom coordinate) the target atom for the beginning, intermediate, and end geometry? Or surrounding atoms around target atom? For now I'm not inducing any freeze to any atom in my NEB setting, but I'm curious if freezing helps convergence of NEB calculation.

Thank you


texts: Can alloys or ceramics have higher density than elemental solids?

texts:
Are there any examples of alloys or ceramics that have higher density than their densest elemental constituent?  If so, do they have unusual or difficult synthesis processes?  If not, is it provable that this is not possible, or demonstrably unlikely.

Since homogeneous metals are essentially crystals in their solid phase it seems plausible that, in theory, there are elements that could fit within the crystal structure without altering it to increase their density.

This would be particularly interesting for metals that are used in applications primarily for their density: e.g., lead, tungsten, and uranium.


texts: Guidance on Jacobian computation for stiff chemical mechanisms

texts:
I'm writing an implicit solver that will involve evaluating the chemical source terms in the system for a given reaction mechanism. It's safe to assume that these mechanisms may be stiff. I know, in general, how to approach the problem but I am looking for some very specific guidance.

The scheme requires the computation of the source-term Jacobian. The mechanism takes in the state variables (pressure, temperature, density) and the species mass fractions then returns the change in partial density of each species. The Jacobian will be computed numerically and I know how to do that in general.

Specifically though, are there any guidelines or requirements on how large (well, small really) the perturbations should be when evaluating the Jacobian numerically? Let's say the perturbation is defined relative to the size of the variable, so let's say the perturbation is X% of the variable. How should X be chosen? Should each variable have its own X or will a global one work? It should work in a mechanism-agnostic way, but I know most mechanisms will be very sensitive to temperature because it is in the exponential and less sensitive to changes in density or mass fraction since those are raised to exponents which are not excessively large.

I understand the idea behind the Jacobian and the Taylor Series expansions, so I'm looking more for practical advice in terms of accuracy, performance, and stability.


texts: How can you tell if a sugar is D/L in its chair form?

texts:
I'm having trouble determining if sugars are D/L in their chair forms. My textbook has generously provided this image of D-Glucose.

So I know that from the fischer, when I put everything into a chair view, the things on the left point up, and the things on the right point down.

However, what about the bottom $\ce{CH2OH}$ group. Which way does it point, and does it determine D/L in a ring? I'm imagining "rotating" all the groups 1 position over clockwise (does it matter if its clockwise/counterclockwise? How do you know which way to spin it?) such that the hydroxyl is now where the $\ce{CH2OH}$ was, H is on the right and $\ce{CH2OH}$ is on the left.

Does that sound right? I can vaguely remember this from high school, but it's become very clouded.


texts: Acid catalysed mechanism of the addition of alcohols to alkenes

texts:
I believe that this mechanism is false.
The protonated ether would in my opinion give a proton to methanol rather than $\ce{H2SO4}$ because the protonated $\ce{CH3OH}$ is more stable than $\ce{H2SO4}$.
Can someone confirm my thought?


texts: Will ipso substitution work in both cases of vanillic and isovanillic acids here or not?

texts:
What will be the product of the 2 reactions when bromine is taken in excess?

I think ipso substitution will work here and there will be two $\ce{Br}$ substituting in both products, but in the book it was given that there will be three $\ce{Br}$ in the second one. I cannot understand why.


texts: What is the geometrical structure of Pb3O4?

texts:
I'm confused by the structure of Pb3O4. There are some sites claiming that it is a six membered ring of alternating Lead and Oxygen atoms with another Oxygen atom in the center bonding with 2 out of the 3 Lead atoms.

There are other sources which claim that it is actually two 4 membered rings of alternating lead and oxygen atoms with a lead atom in common between the 2 rings.

Moreover, isn't Lead a metal? Then How can it combine with oxygen in such "bonds" whereas ionic bonds are non-directional?


texts: How do I figure out the amount of water (mL) and amount of Aluminum (g)?

texts:
We have a project where we have to extract copper from copper sulfate. But my group is given a powder version ($5~\mathrm{g}$), so we have to first dilute it with water and then combine it with aluminum to extract the copper. If this is the equation:

$$\ce{3Cu(SO4) + 2Al + H2O + salt -> Al2 (SO4)3 + 3Cu}$$

Salt is acting as a catalyst for the experiment.


texts: Clogged drain, commercial products are ineffective

texts:
I have a clogged drain from my shower. Commercial products like Savo or WC Net totally don't work. Is there any chemical substance which can be bought without permission or which can be made easily to clear the drain?

I live in Czech Republic, it's part of European Union, just for your information about the law system here (can be helpful to decide what's legal).

My first idea is sodium hydroxide, is it powerful enough?


texts: How does the Freezing Point fall in a solution?

texts:
It is known that addition of a non-volatile solute to a volatile solvent(liquid) to give a solution reduces the Vapour Pressure of the solution (well solvent actually as only solvent is volatile).

This leads to the Elevation of Boiling Point and "Deppresion" of Freezing Point.

I am clear with elevation of BP. But it is said that a liquid freezes when the vapour pressure of the liquid phase attains the vapour pressure of its solid state.

So, how possibly does the freezing point falls? For instance let the Vapour Pressure of the solid state be at an arbitrary point "x"(at a temperature A Kelvin) and that of the liquid phase be at "y".

So when we add a solute to the liquid:

Vapour pressure of liquid(solution) = y - $\alpha $ (where $\alpha $ is the depression in the vapour pressure)

So now the vapour pressure of the liquid(solution) reaches "x" rapidly that is at a higher temperature or a temperature greater than A which is an elevation in the freezing point.

I am always confused with this part.


texts: The answer makes sense to me. However, what if $\ce{OsO4}$ were to attack from the other side of the double bond? Why does the answer key not show that possibility? Would we not get an other molecule?


texts: Reacting carbon dioxide with magnesium in ribbon form

texts:
My experiment involves a reaction of magnesium in ribbon form with that of carbon dioxide. I know that the product shall be magnesium oxide (white powder) and carbon (black powder) but I do not know what kind of carbon it actually is (allotrope, purity, etc.)

It would also help if you can suggest a method for separating the carbon from the magnesium oxide after the reaction.


texts: Low viscosity, low surface tension liquid for volume measurement

texts:
General Case
This question concerns the general problem of accurate volume measurement of a given object. Among other techniques, that of liquid displacement is sometimes used for this purpose.

In case of a solid material, the latter may be immersed in liquid, and its volume calculated by measuring the amount of fluid displaced in a graduated cylinder.

In case of a hollow object, the latter may be filled in with a liquid which amount is accurately determined, either while filling in, or by emptying the object in a graduated container a posteriori (or - maybe more accurately - by weighing).

In both cases, the choice of the liquid is of crucial importance for the accuracy of the measurement.
Specific Issue
I have a CO2 gas sensor with a complex hollow embodiment, also containing electronics, and since I wish to perform response time measurements, I would like to precisely know its inner volume. I came up with the idea of filling it with a liquid, as stated above. I do not have and cannot have accurate drawings of the inner sensor.
Questions
1. Is there other methods to perform such a volume measurement which may be preferable?
Indeed, I came up with this idea because I find acceptable to sacrifice a sensor to perform such volume measurements. Alternatively, I also thought of placing the sensor in a closed, accurately known volume, along with some amount of chemical reagents that would produce a given amount of CO2. Then, by dilution and measurement of the CO2 percentage inside the enclosure, I may know the volume occupied by the sensor. However, I believe that there are far too many sources of errors in such procedure for it to yield accurate results. I may be wrong, though, and other variations of the latter idea may work well...
2. Which liquid may be the best for such measurement?
This is the main issue here. I would tend to say that such a liquid should have both a low surface tension and a low viscosity. Additionally, low volatility would be a plus, since it would prevent the amount of poured liquid to decrease with time. I find methanol or ethanol to be good canditates despite their high-volatility. I cannot use acetone because of the risk of plastic dissolution and the resulting leakage of the sensor's embodiment. Would you know of a more suitable liquid, possibly readily available in the lab?
3. Can surfactant be added to ethanol or methanol? If so, do they further decrease surface tension? Which are they?
A quick search in the literature revealed that methanol or ethanol are themselves considered as water surfactant. Their mixture with other surfactants is often analysed in emulsions of oil, or other chemicals, but not alone.
Related topics:

Non-wetting fluids for precise volume measurements
Looking for a non-volatile liquid less viscous than water

Edit:

As pointed out by Poutnik, low volatility and low viscosity are mutually incompatible with each other. Indeed, low viscosity tends to be positively correlated with high volatility, both of them being the consequence of low intermolecular forces. More resources on the topic are available here (saved version). The requirement on low volatility was not mandatory though, as it was just to ensure that not too much of the liquid evaporates during the filling of the sensor...


texts:
It seems that reaction rate is defined as change of concentration over time
and the speed doesn’t change if you add more solid. But imagine we have a cube (1 kg) of $\ce{CaCO3}$ that yields 1 mole $\ce{CO2}$ in $t$ seconds and we have another cube (5 kg) of $\ce{CaCO3}$. Does this one also yield 1 mole $\ce{CO2}$ in $t$ seconds? (my teacher said yes)

But if we think of second cube as 5 separate 1 kg cubes, then each one again yields 1 mole per $t$ seconds, making it 5 moles of $\ce{CO2}$ in $t$ seconds.

So which one actually happens and is the speed the same?


texts:
I have no idea of chemistry, just a little bit what I know from school, but I found through some search some connection between entropy (Shannon entropy) of the divisors of some natural numbers and the Madelung constants.

My question is this:

Are these numbers Madelung constants?

1 -0.000000000000000
2 1.38629436111989 ( http://oeis.org/A016627 )
3 1.38629436111989
4 3.31573052232910
5 1.38629436111989
6 5.54531864369184  ( http://oeis.org/A257872 )
7 1.38629436111989
8 5.57849454296371
9 3.29975689063759
10 5.54521210457048
11 1.38629436111989
12 10.7943529563000
13 1.38629436111989
14 5.54518969515687
15 5.54519368543309
16 8.08924328274917
17 1.38629436111989
18 10.7599543952466
19 1.38629436111989
20 10.7921021686465

Thanks for your help!

Related question:
https://mathoverflow.net/questions/346239/entropy-magnitude-diversity-of-finite-metric-spaces-in-number-theory

Edit:
I think I found an explanation for the numbers ( entropy ). It is approximately:

$\tau(n) \log(\tau(n))$, where $\tau(n)$ is the number of divisors of $n$.

So the $1.386$ and $5.545$ are just coincidences with Madelung constants I think.


texts: Endothermic Reaction with Specific Details

texts:
I need some information for a book I'm writing.

Let's say you're in a confined space, about 8 feet by 8 feet. The area is being heated externally slowly (a few degrees a minute) to about 3,100 degrees F (1700 C). You have ammonium thiocyanate, $\ce{NH4SCN}$, and barium hydroxide octahydrate, $\ce{Ba(OH)2.8H2O}$, 20 g T. You combine them.

Since the room is getting so hot, would the room get equally cold and equally as fast? If you put the chemicals inside of a crate, closed it up, would it take longer to cool off the room? How long would it take for it to do this? Would the cold kill the person inside the room? (Aside from the ammonia burning the lungs and toxic barium because that's easy to fix in a story)

If there's just no way, is there a different chemical reaction that I could have the character use that won't kill her?


texts: Is it possible to manipulate some specific atoms of a liquid metal by dint of the magnetic field, electric field, etc?

texts:
Let's deem, we have a liquid metal that is multicomponent, for example, type A, B, and C. Is it possible that we single out the type A and put them in a specific shape, for example, a circle?
Let me clarify it, I have a liquid metal, having three different elements, and I poured it in a square framework. I want to separate element C and then set them in several lines that are parallel with each other; so that, they play the role of reinforcement and the alloy of A and B is my matrix.


texts:
I understand that oxidation numbers are a method for keeping track of electrons in a reaction and how they are generally assigned (electrons in a bond are assigned to the more electronegative atom).

Why does this method work? Why does assigning these arbitrary numbers based on electronegativity work in predicting and balancing reactions?


texts: Theoretical limits of (NIR) spectroscopy for quantitative analysis

texts:
Edit (months later): In hindsight, I was asking about the theoretical limits of multivariate curve resolution (see Lawton & Sylvestre: Self-modeling curve resolution) in chemometric applications.

NIR spectra are commonly used to estimate analyte concentrations. The common approach is to measure the spectra of different samples with known concentration (training data) and then estimate the unknown concentrations by regression.

My question is whether we could determine analyte concentrations of any substance just from the following:

1) Infinitely precise spectra of all elements.
2) Infinitely precise spectrum of the sample.

If not, would it help if we relaxed on the NIR range assumption?
If still not, would it help if we knew the spectra of all possible molecules with infinite precision?

The first step in determining the answer is probably determining whether there are two different atoms identical in their spectra. I don't know the answer. Unfortunately my knowledge of physics and chemistry is very limited.


texts: Carbon-Sulfur Bond Lengths; Resonance Effects (Or Lack Thereof)

texts:
Why is the C-S bond in $\ce{CH_2SH^-}$ longer than in $\ce{CH_3SH}$? Wouldn't there be resonance in the former, forcing the C-S bond to contract?

http://www.nrcresearchpress.com/doi/pdf/10.1139/v75-431

Also while we're at it are there any non ab initio calculations/empirical studies on this interesting thiol ion?


texts: Designing synthetic route to dicarbonyl compound

texts:
It's the last one, where 1,4-dimethylcyclohexane breaks apart into... something.

Here's the workup I have. I want to put out there that I'm not concerned about getting the optimal yield yet. Just making the product.

Free radical addition of $\ce{Br}$ to the 2 position.

Removal of that $\ce{Br}$ and the formation of a double bond via E2 using tBuO-

Breaking apart the structure via ozonolysis.

However, no matter where I place the double bond, I can't get the correct configuration of double bonded Oxygens (ketones and aldehydes, right?). So, I must be doing something wrong. Thoughts?


texts: Is the cyclopropenyl anion antiaromatic?

texts:
According to my book, a compound is antiaromatic if it is cyclic, planar, and possesses a fully conjugated system of p-orbitals with $4n$ π-electrons.

However, I have also been told that the cyclopropenyl anion is neither aromatic nor antiaromatic.

How is this so? It has four π-electrons and therefore should satisfy the criteria listed above.


texts: Calculation of entropy for an isothermal irreversible expansion

texts:
How do I calculate the entropy change for an irreversible isothermal expansion against $p_\text{ext}=p_0$?

For a reversible isothermal expansion we know $\delta S_\text{uni}=0$ so $\delta S_\text{sys}=-\delta S_\text{surr}=nR\ln\frac{V_\mathrm f}{V_\mathrm i}$

However I can't figure out why $\delta S_\text{sys}=nR\ln\frac{V_\mathrm f}{V_\mathrm i}$ remains for irreversible expansion.

I also found out an equation for irreversible expansion
$\delta S_\text{uni}=q_\text{rev}/T-q_\text{irrev}/T$
Is it correct? If yes? Can you explain how do we get it?

Edit

Is this correct ?

$\delta S_\text{uni}=\delta S_\text{sys}+\delta_\text{surr}$

$\delta S_\text{sys}=\frac{q_\text{rev}}{T}$

$\delta S_\text{surr}=-\frac{q_\text{irrev}}{T}=p_\text{ext}\delta V/T$


texts: I am trying to get a better intuition on solid-state physics but I am a chemist by degree. I came across this article that attempts to bridge the gap between solid-state physics and molecular chemistry. However, I am unsure what the author is referring to when he says "a and an e combination". I believe it is talking about the symmetry of the pi orbitals but I really have no clue.


texts:
I am preparing for A level chemistry exams. One of the questions I came across is

  Calculate the $M_\mathrm r$ of unknown monoprotic acid. The volume is $15\,\rm cm^3$ and concentration $10.95\,\rm g\cdot dm^{-3}$.

I know how to calculate the number of moles and I know the equation to calculate $M_\mathrm r$ but could anyone give me some guidance on how to calculate the mass from this data?


texts: What is the best way to clean Lovibond tintometer quartz cuvette used for oil?

texts:
I work in a laboratory where we regularly check edible oil color by using a Lovibond colorimeter. Some people suggested me to wash the quartz cuvette using soap solution.
But I am thinking about washing the quartz cuvette by using acetone solution and then leave it to dry in air. Is this method correct?


texts:
On regular paper, ink is absorbed, while on photopaper ink stays at the surface and dries for a longer time. What forces act in these two different cases?

(see also related questions about pencil marks and colorants)


texts: Why do people assume 28 oxygens in chlorite mineral formula?

texts:
I have been trying to calculate chlorite mineral formulas from microprobe data. However, all of the mineral formula spreadsheets on the internet, including those from the Open University assume 28 oxygens (http://www.open.ac.uk/earth-research/tindle/AGT/AGT_Home_2010/Microprobe-2.html)

However, all the formula I have ever seen for chlorite only have 18 oxygens? (see DHZ or http://www.mindat.org/min-1016.html)

By then calculating my formula assuming 28 oxygens, it means I have easily more cations than the mineral structure would have sites for?

Many thanks for any help


texts: I can't find reaction enthalpy ∆H for water formation reaction

texts:
$$\ce{1/2 O2(g) + H2(g) → H2O (l)}$$

The tabulated value is $\Delta H = \pu{−285.8 kJ/mol}$

I'm using the bond energies values for each molecule and for some reason, I am getting a different result, not even close to $\pu{-285 kJ/mol}$.

Bond dissociation energies:

$\ce{H-H} = \pu{436 kJ/mol}$

$\ce{O=O} = \pu{499 kJ/mol}$

$\ce{O-H} = \pu{464 kJ/mol}$

My attempt to calculate from bond dissociation energies:

(500.1/2) + 436 → 464.2

250 + 436 → 928

($∆H$ found is positive)


texts: Calculating Solubility Product of AgCl from electrode potential

texts:
I have to use a measured electrode potential to find the solubility product of $\ce{AgCl}$. In our experiment, we first mixed one drop of $\pu{1.0 M}$ $\ce{AgNO3}$ with $\pu{10 mL}$ of $\pu{1.0 M}$ $\ce{NaCl}$ to precipitate $\ce{AgCl}$. For the purposes of our experiment, we are to assume that the concentration of $\ce{Cl-}$ remains $\pu{1.0 M}$, and use the Nernst equation to determine the value of $\ce{[Ag+]}$. The reaction that occurred in our cell was between $\pu{1 mL}$ of the solution of $\ce{Ag+}$ and $\ce{Cl-}$ left behind from the precipitation reaction described above, and $\pu{1 mL}$ of of $\pu{0.10 M}$ $\ce{Zn^2+}$. The reactions were all carried out at $\pu{25 ^\circ C}$, and the voltage obtained by our group was $\pu{0.85 V}$.

My Method

The half-reactions going on in this cell were:
\begin{align}
 &&\ce{2Ag+(aq) + 2e- &-> 2Ag(s)} & (E^\circ &= 0.80)\\
+&&\ce{Zn(s) &-> Zn^2+(aq) + 2e-} & (E^\circ &= 0.76)\\\hline
 &&\ce{2Ag+(aq) + Zn(s) &-> Zn^2+(aq) + 2Ag(s)} & (E^\circ_\mathrm{cell} & = 1.56)
\end{align}

From here, I used the Nernst equation to solve for $\ce{[Ag+]}$, with $n=2$ moles of electrons transferred and $Q = \ce{[Zn^2+]}/\ce{[Ag+]^2}$:

$$0.85 = 1.56 - \frac{0.0592}{2}\log\frac{0.10}{[\ce{Ag+}]^2}$$

Solving this for $\ce{[Ag+]}$ yields approximately $3.21 \times 10^{-13}$.

I then applied the law of mass action to determine the solubility product of $\ce{AgCl}$: $$ \ce{[Ag+][Cl^{-}]} = [3.21 \times 10^{-13}] \times [1.0] = 3.21 \times 10^{-13} $$

However, this number is quite different from the expected value of $1.8 \times 10^{-10}$. I am wondering if my math or approach is wrong or if my  group's data is simply wrong?


texts: In sulfate conjugation , is it considered as a carrier or help to make sulfonation if I got a question and I have to choose ( enzyme helps to make the reaction or is a carrier to transfer the sulfate ) I know isn't an enzyme but it does help in the reaction , that what I understand


texts: Why isn't Perkin reaction possible with aliphatic aldehydes? Since the carbon atom of carbonyl group of aliphatic aldehydes is more electrophilic than that of aromatic ones, the reaction must be more feasible in case of aliphatic compounds. Please explain.


texts: Can it be said that on our planet we have roughly the same number of electrons as we have protons?

texts: My question is quite simple I think. Is it true that we have approximately the same number of electrons as we have protons and the average electric charge of the molecules in our planet is roughly neutral?


texts:
I've always seen benzyne (benzene with a triple bond) classified as an "intermediate". I really don't see why it needs to be an intermediate, though. The possible reasons I can come up with are flimsy:

It has an unstable sp2–sp2 $\pi$ bent bond: we have bent bonds with more angle strain in cyclopropane, which is not an intermediate. Though those bonds are $\sigma$ bonds.
It immediately reacts with itself to form a dimer, biphenylene, in the absence of other reagents: there are many other molecules which spontaneously dimerize (eg $\ce{NO2}$ at certain temperatures), yet they are not classified as "intermediates".

So, what makes benzyne an "intermediate"?

More generally (but possibly too broad), what makes a molecule an "intermediate"?


texts: Why does the titanium go to the tungsten filament in the crystal bar process?

texts:
I've tried to read a report by the US atomic energy commission [1], but couldn't really find the answer, or maybe I missed it.
Why is the gaseous titanium deposited on the tungsten wire/filament during the van Arkel–de Boer process?
Reference

Petersen, A. W. Preparation of Metallic Titanium by Film Boiling (Thesis); UCRL-2523, 4393936; United States, 1954. DOI: 10.2172/4393936.


texts: Are there processes to standardize the shape of a crystal during crystallization?

texts: I am trying to standardize the shape of europium dibenzoylmethide triethylammonium (EuD4TEA) during its crystallization process. I'm a mechanical engineering student and am not too familiar on the details of crystallization. Is there a process for creating crystals of standard size, shape, and weight? If so, would the process vary between what I am using and any other type of crystal?


texts:
I have recently come across the concept of semiconductor Li-ion batters, for instance carbonised polyacenic semiconductor (PAS) Li-doped materials.

I am not sure how common it is for a battery to be formed of a semiconductor, and are their any other examples?

Do all Li-ion polymer batteries involve a semiconducting component?

How do these differ from metallic batteries?

Is there an advantage?


texts: Why is heroin a more potent drug than morphine, despite having a similar structure?

texts:
The structures of heroin and morphine are quite similar, with heroin being formed by acetylation of morphine:

Why is heroin so much more potent than morphine, when their structures are so similar? What biochemical effects lead to heroin's prevalence as a recreational drug, and consequently, the much higher number of fatalities from overdosing on heroin as compared to morphine.
This Source has an attached reference1, which claims the following:

It has been reported that Diamorphine is twice as potent as morphine .
...
We found no significant differences between the groups over a 24-hour period in the degree of euphoria, nausea and vomiting or sedation, as assessed by subjective visual analogue scores, or in pain relief, nausea and euphoria as assessed by verbal rating. There was, in addition, no significant difference in the requirements for antiemetics between the two groups. Both groups demonstrated relatively low nausea scores. The mean amount of morphine demanded was approximately twice that of diamorphine.
...
The scientific basis for the alleged superiority of diamorphine over morphine is dubious and since diamorphine is metabolised to monacetyl morphine, and morphine itself, it would be surprising if there were a marked difference. Very few studies authenticate this claim of superiority and the present study is no exception.

This does not explain the prevalence of heroin compared to morphine. Over 15,000 people died in the US from heroin overdose2, whereas the number for morphine is quite less. Are the reasons behind this purely sociological (easier access to heroin compared to morphine), or is there some chemistry that I am missing out on here?
References:

Robinson, S. L., et al. “Morphine Compared with Diamorphine.: A Comparison of Dose Requirements and Side-Effects after Hip Surgery.” Anaesthesia, vol. 46, no. 7, July 1991, pp. 538–40. doi:10.1111/j.1365-2044.1991.tb09650.x.
CDC Heroin Overdose data. Link.


texts: Effect of steric effect on acidic and basic strength

texts:
I found a sentence given in my textbook:

More is steric effect more is acidic strength of carboxylic acids and
more is steric effect less is basic strength of aniline and other
amines.

Could someone please explain with an example?
I guess it might seem I am asking about ortho effect but I am not. I have gone through the post suggested but I am basically asking about subcases of ortho effect as in if we are asked to compare between ortho tertbutyl benzoic acid and ortho methyl benzoic acid then how would we go about it?  Or suppose the questions asks comparing the basic strength between orthotert butyl amine and ortho methyl amine how would we do it ?


texts:
I've tried looking here, but I can't figure it out.

As a start, what is just the cobalt and cyclopentadienyl anion compound called.
How does that name get added to the trimethylphosphine and carbonyl groups.

I want to ask further questions about this compound on chemistry stack exchange, and I think it would be a good idea to be able to use the name in those questions.


texts: What is the correct reaction of sulfur dioxide with chlorine?

texts:
I'm confused in reaction of $\ce{SO2}$ with $\ce{Cl2}$. Some source states the given reaction (1), while others state the reaction (2):

$$\begin{align}
\ce{SO2 + Cl2 &-> SOCl2 + Cl2O \tag{1}}\\
\ce{SO2 + Cl2 &-> SO2Cl2 \tag{2}}
\end{align}$$

While I read in NCERT Chemistry 12 part-II page-198 that chlorine oxidises $\ce{SO2}$ to $\ce{SO3}$. I wish to know the specific condition in which the particular reactions will occur.


texts: How to know when subscripts refer to charges or not

texts:
My question is very easy. Sometimes to determine to charge of a compound you multiply the charge by the number of ions you have of that element. But sometimes it seems as if you don't do it this way. Example:

$\ce{Ba(BrO2)NO2} = \ce{Ba^2+ + BrO2^0 + NO2^-}$: Here you multiply the subscript by the charge of 1- in order to balance it
$\ce{KNaCO3} = \ce{K+ + Na+ CO3^2-} $: here you don't multiply the subscript 3 by the charge 2- for it to be balanced.

Could someone please explain the difference? When do you mdo a multiplication and when not?


texts: Alternative python modules to RDKit to convert SMILES to structure

texts:
Python module RDKit is great, but it cannot be installed by pip, and therefore it is difficult to use it sometimes in a virtual environment.

I am wondering that if there are some alternative python modules that can convert smiles to chemical structures?


texts: What is the meaning when it is said "Temperature of an Oxyacetylene Torch is 3500 degrees Celsius"?

texts:
I don't think flame is anything but the product at that temperature but I am not sure. What exactly is flame? And I think the correct statement should be that the exothermic reaction here produces heat at such level that the temperature of the product gas reaches 3500 degrees.
What will be the exact idea behind the statement?


texts: CaCl2 and Citric Acid react /w metal pot

texts:
I'm building a dehumidifier based on $\ce{CaCl2}$-solution as descant, which is to be regenerated by heating and evaporation.
I thought it would be a good idea to add some citric acid to combat chalk-buildup due to rather hard tap water.
To test for possible reactions of $\ce{CaCl2}$ and citric acid, I mixed a 30% $\ce{CaCl2}$ solution by weight, added different amounts of acid (10%, "rather more", "very much") and boiled them. (My main fear being that some Ca might react with Citric acid to form a precipitate, which did NOT happen.)
While heating, the solutions with more citric acid turned dark turquoise, but remained clear. Using vinegar did not cause a color-change. Heating $\ce{CaCl2}$ or citric acid alone does not cause color change. No other reactants (I know of) were present. It seems that cooking for longer turns the solution darker, but I may be mistaken on that.
The reactions I could think of should all be colorless/white, not blue/green/turquoise: Ca-citrate, decomosed citric acid, I didn't find sources for citric $\ce{Ca}$ complexes. Maybe a $\ce{Cl}$-complex is formed, but $\ce{Ca}$  is the only available metal, and again I couldn't find resources for chlorine $\ce{Ca}$ complexes. Impurities are probably not at fault, since the color is very strong/dark.
What I'm asking is specifically what reactions might occur between $\ce{CaCl2}$ and citric acid. I know of enough ways to get around my hard-water problem.
Edit:
The pot I used for heating was at fault. Heating in an enamel pot showed no color change. Thanks @poutnik and @m-farooq
I would still be very curious as to what reaction might cause a green/blue color change. From what I can tell, the metal pot is made of stainless steel.


texts: Can someone clear this confusion I have about the first law of thermodynamics

texts: In our school we were taught that the first law of thermodynamics represented mathematically is $\Delta U=Q+W$. Also we were taught that for an isothermal process $\Delta U=0$ and therefore $Q=-W$, but we were taught that for an isothermal free expansion of a gas against vacuum $W=0$ and therefore $\Delta U=Q$ but shouldn't $\Delta U$ be zero here as well, I mean after all the process is still isothermal. Can somebody pls help with regards to this, also pls try to explain in a simple manner (High School Level). Thanks for the help


texts:
I have gone online to see many times that the electrolysis of $\ce{NaCl}$ dissolved in water produces Lye: $$\ce{2NaCl + 2H2O -> 2NaOH + H2 + Cl2}$$ Other times $\ce{NaClO3}$ or some other compound. I just want to know with one solid answer (anyone), what does this reaction produce?

Thank you.


texts:
When my family buys powdered cloves in bulk, we put them in plastic until we get home - which takes at very most an hour. As soon as we get home, we transfer them into glass because we have had issues with them eating through the plastic cups until they are soft and have holes in them - this takes maybe a week.

I do not know exactly what type of plastic the cups are made out of; if this helps, they have the recyclable number 6 on them.

So, my question is, what is it in the cloves that is causing them to eat through the plastic at such a high rate? Are they really acidic? Or is it perhaps due to their oils?


texts: How might ammonia be created in this mechanochemical reaction?

texts:
Can mechanical agitation catalyze reactions?  It appears so (thanks to Mithoron for the pointer!).

We observed the following: We were using 10-micron hBN powder to impact-plate copper bearings (e.g., by running them together in a vibratory tumbler, and other similar processes).  Even though the mechanical processes ran in a standard atmosphere and did not exceed 60C we consistently observed that ammonia was released.  As a control:  I have run the same copper with all sorts of other media through the same mechanical processes and never detected ammonia.

Our conclusion is that the BN is decomposing during the mechanical processing.  But hBN is very thermally and chemically stable: hBN doesn't react with Cu below 1000C!

So is it plausible that mechanical abrasion at this low a temperature would break the B-N bond?  If so, what subsequent reactions (again, in a standard atmosphere) might cause the free N to form $\ce{NH3}$ in detectable amounts, instead of just forming $\ce{N2}%edit$?


texts: Any differences in metal ion emission spectra?

texts:
If I measure the emission spectra of potassium using the following solutions

1) $0.1~\mathrm{M}$ of $\ce{KNO3}$

2) $0.1~\mathrm{M}$ of $\ce{K2SO4}$

will I see any significant differences?

I think there will be no significant differences because the spectrum does not depend on whether in 1) I am using $\ce{K}$ while in 2) I am using $\ce{K2}$ (the emission spectrum should be independent). Am I right?


texts: Why it is hard to rinse off soap from your body using rain water

texts: I have experienced this when every time I take a bath using rain water, I just can't stop wondering why is it really hard to rinse off soap from your body?


texts: How to determine the composition of a gas mixture after a combustion?

texts:
The problem is as follows:

  A mixture of gases consisting of $\ce{CH4}$ and $\ce{C2H4}$ is let to pass over red hot
  $\ce{CuO}$. Then $\pu{0.6g}$ of $\ce{H2O}$ is collected along $\pu{1.185g}$ of
  $\ce{CO2}$. What will be the composition of the mixture if it is known
  that the combustion was complete?.

The alternatives given in my book are as follows:

$\begin{array}{ll}
1.& \ce{CH4}=51.8\%\,and\,\ce{C2H4}=48.2\,\%\\
2.&\ce{CH4}=50\%\,and\,\ce{C2H4}=50\,\%\\
3.&\ce{CH4}=33.3\%\,and\,\ce{C2H4}=66.6\,\%\\
4.&\ce{CH4}=38.8\%\,and\,\ce{C2H4}=64.2\,\%\\
5.&\ce{CH4}=36.3\%\,and\,\ce{C2H4}=63.7\,\%\\
\end{array}$

I'm not sure exactly how to proceed with this question. Should it be treated as if it is an analysis by combustion?.

What I did to solve this was to treat each gas in the mixture as reacting independently for the oxygen from interacting with the red hot $\ce{CuO}$ as follows:

$\ce{ CH4 + 2 O2 -> CO2 + 2 H2O}$

With: $x=\ce{ CH4}$

$x\,g\times\frac{1\,mol\,\ce{ CH4}}{16\,g\,\ce{ CH4}}\times \frac{2\,\,mol\,\ce{ H2O}}{1\,\,mol\,\ce{ CH4}}\times\frac{18\,g}{1\,mol\,\ce{H2O}}=\frac{18}{8}x\,g\,\ce{H2O}$

$x\,g\times\frac{1\,mol\,\ce{CH4}}{16\,g\,\ce{CH4}}\times \frac{1\,\,mol\,\ce{CO2}}{1\,\,mol\,\ce{CH4}}\times\frac{44\,g}{1\,mol\,\ce{CO2}}=\frac{44}{16}x\,g\,\ce{CO2}$

For:

$\ce{C2H4 + 3 O2 -> 2 CO2 + 2 H2O}$

With $y=\ce{C2H4}$

$y\,g\times\frac{1\,mol\,\ce{C2H4}}{28\,g\,\ce{C2H4}}\times \frac{2\,\,mol\,\ce{H2O}}{1\,\,mol\,\ce{C2H4}}\times\frac{18\,g}{1\,mol\,\ce{H2O}}=\frac{36}{28}y\,g\,\ce{H2O}$

$y\,g\times\frac{1\,mol\,\ce{C2H4}}{28\,g\,\ce{C2H4}}\times \frac{2\,\,mol\,\ce{CO2}}{1\,\,mol\,\ce{C2H4}}\times\frac{44\,g}{1\,mol\,\ce{CO2}}=\frac{88}{28}x\,g\,\ce{CO2}$

This is reduced to a system of equations as follows:

$\frac{44}{16}x+\frac{44}{14}y=1.185\,g\,\ce{CO2}$

$\frac{18}{8}x+\frac{18}{14}y=0.6\,g\,\ce{H2O}$

Solving this system yields:

$x=0.1024\,g\,\ce{CH4}$

$y=0.2874\,g\,\ce{C2H4}$

Then to calculate the composition of the mixture I would use the molar fraction:

$n_{\ce{CH4}}=\frac{0.1024}{16}=0.0064\,mol$

$n_{\ce{C2H4}}=\frac{0.2874}{28}=0.01026\,mol$

Then the percentage for composition for $\ce{CH4}$ would be:

$\frac{n_{\ce{CH4}}}{n_{\ce{CH4}}+n_{\ce{C2H4}}}=\frac{0.0064}{0.0064+0.01026}=0.3841$

For $\ce{C2H4}$:

$\frac{\ce{C2H4}}{n_{\ce{CH4}}+n_{\ce{C2H4}}}=\frac{0.01026}{0.0064+0.01026}=0.6159$

To which correspond each one as roughly $38.41\%$ and $61.59\%$ respectively for $\ce{CH4}$ and $\ce{C2H4}$. But none of this seem to check with any of the answers.

Could it be that my method was wrong or did I overlooked something?.

The only answer which is closer to mine is the forth alternative but the second number is off by a big margin thus I'm not very convinced on my result. What would be the recommended procedure in this case?

Can somebody help me here?.


texts: Why can we use standard entropy when determining temperature at which a reaction becomes spontaneous?

texts:
In this chemistry problem, $\Delta H$ and $\Delta S$ are given at $298\text{ K}$, and it asks for the temperature at which the reaction becomes spontaneous:

  For the reaction $2\text{SO}_3 \rightarrow 2\text{SO}_2 + \text{O}_2$, $\Delta H_r^\circ = +198 \text{ kJ/mol}$ and $\Delta S_r^\circ = 190 \text{ J / mol}\cdot\text{K}$. At what temperature will the forward reaction will become spontaneous?

I understand to solve this problem; the Gibbs free energy equation,
$$\Delta G = \Delta H - T \Delta S,$$
can be used to determine the temperature by assuming $\Delta H$ and $\Delta S$ are constant and solving for $T$ when $\Delta G = 0$. This gives $T = 1042\text{ K}$.

However, I don't understand why is this assumption valid. Isn't it true that $\Delta S_r$ would change at different temperatures? Why is it that the value for $\Delta S$ for this reaction under standard conditions can be used to calculate $\Delta G$ at $1042 \text{ K}$?


texts: Is it true that "Voigt Circuit" would be able to be fitted to various electrochemical impedance spectra?

texts:
"Voigt Circuit" which is a series combination of Voigt elements (i.e. parallel RC's), is commonly used for Kramers-Kronig relations checking; and as I imagine it is generally believed to be able to be fitted to various electrochemical impedance spectra?
Is this belief true or not?
And if the answer is "Yes", is there any theoretical basis for that or it is only a practical sense (I mean that it is approved according to fitting results of experimental data to Voigt circuit)?


texts: Formal charge: size vs electronegativity?

texts:
My question is why size is not taken into consideration when deciding major contributors of resonance structures, particularly: why is the formal charge always assigned to the most electronegative atom, but not necessarily to the one that can "better hold a negative charge"?

Example: Thiocyanate. Everywhere I've found says the major resonance contributor is that where the
negative charge lies on the nitrogen atom due to the higher electronegativity of $\ce{N}$ vs $\ce{S}$, but when we talk about acids/bases, clearly $\ce{H2S}$ is a stronger acid than $\ce{NH3}$ due to the "better stabilization of the negative charge by the sulfur atom due to its larger size/polarizability" (or so we teach in every OChem course). So why do we disregard this fact when assigning formal charges?

PS. I'm aware formal charges are an artificial construct and do not necessarily represent real-life electron density, I am just curious about these rules from an educator's perspective.


texts: What is the reason for the different solubility of silver halides in ammonia?

texts:
According to my knowledge, I know that $\ce{AgCl}$ dissolves in dilute ammonia, $\ce{AgBr}$ dissolves in concentrated ammonia and $\ce{AgI}$ does not dissolve even with concentrated ammonia.

What is the reason for this?


texts:
How many distinct dichlorination products can result when isobutane is subjected to free radical chlorination?

I think that three distinct products may result namely
a) 1,1-Dichloro-2-methylpropane
b) 1,2-Dichloro-2-methylpropane
c) 1,3-Dichloro-2-methylpropane

But the book says only two distinct products may form. Can anyone explain how?


texts: Is the IUPAC name of $\ce{CH3CH=CH-C#CH}$ pent-3-en-1-yne or pent-2-en-4-yne?


texts: Mechanism for the formation of an alkyl halide from alcohol and phosphorus trihalide

texts:
I was reading about synthesis of alkyl halides from $\ce{PX3}$. I want to know the mechanism for this reaction. According to Solomons and Fryhle, no rearrangement takes place in case of $\ce{PBr3}$ , which leads me to think that the mechanism is SN2. But what about phosphorus bromides and iodides?

A Google search confirmed that the mechanism for reaction with phosphorus tribromide is indeed SN2, but I could not find anything on trichlorides and iodides. I need help for those.

Thanks.


texts: Basis set in the computational software "Gaussian-03" for studying adsorption of a hydrogen atom on a carbon paste electrode dropcasted with Pt-CNT

texts: What is the basis set in the computational software "Gaussian-03" that can be used to study the interaction of $\ce{H}$-atom with $\ce{Pt-CNT}$ dropcasted electrode? How can we study the energy differences that arises due to the interaction computationally?


texts:
We know that phenol and aniline, despite being strongly activating, are unable to to undergo Friedel-Crafts reactions because they form complexes with $\ce{AlCl3}$, thanks to the lone pair on nitrogen and oxygen atoms.

However, according to my notes (and Google) anisole does undergo Friedel-Crafts reactions. How can it be possible, why is there no complex formation this time?

Also, I wanted to know how can we say that a certain group like $\ce{OH}$ will surely form a complex? Is containing a lone pair a sufficient condition?


texts: Why does titanium have lower affinity than scandium?

texts:
Electron affinity of atoms in the same row usually increases with the atomic number until the shell or half-shell gets full, and then it drops down. Some transition metals are exceptions from the rule, but the strangest exception to me is Titanium: while scandium ($3d^1$) has an affinity of 18 kJ/mol, titanium ($3d^2$) has an affinity of 8 kJ/mol.
It does not seem to make sense: the effective charge of titanium nucleus should be larger compared to scandium (Slater's rule), and exchange energy also favors titanium.
Does anyone have a good explanation?


texts: Are alkenes or alkynes reduced first with diimide?

texts:
I know that $\ce{NH2NH2}/\ce{H2O2}$ is used as an reducing agent for selective reduction of alkenes and alkynes. $\ce{NH2NH2}$ reacts with $\ce{H2O2}$ to form diimide ($\ce{N2H2}$), which then undergoes a percicylic mechanism with the alkene/alkyne to give the reduced product.

My textbook had this question: what does the reaction of but-1-en-3-yne (vinylacetylene) with 1 equivalent of $\ce{N2H2}/\ce{H2O2}$ give?

Now my question is which reacts first? I know that in electrophillic reactions the alkene has greater reactivity than the alkyne but this is a pericyclic mechanism so i am not sure about it. The given answer is that alkene part reacts, not the alkyne.


texts: Trying to synthesize and crystallize iron (iii) ammonium sulfate

texts:
I've been following instructions (from here, the first method) to synthesize iron (iii) ammonium sulfate and crystallize it. The first attempt was a fail, I spilled most of my solution and what I managed to save crystallized green from a dark yellow-brown solution. I tried again, first reacting the iron (in the form of filings) with the sulfuric acid, then adding the ammonium nitrate dissolved in water and allowed to warm to room temp. There was no immediate reaction when I added the amm. nitrate but the solution changed color slowly over the next few days to a dark green-yellow. When crystals finally started forming, they were green. NH4Fe(SO4)2•12H2O should crystallize out as a pink/purple color, whereas the iron (ii) compounds crystallize green, with the regular sulfate being blue-green and Mohr's salt being a darker green. I believe I got the latter.

Basically I'm confused as to why I seem to have gotten iron (ii) ammonium sulfate rather than the iron (iii) variant. I'm going to try again for iron (iii) but with sulfates or iron (ii) and ammonium to start, I just had ammonium nitrate on hand. I can put up pictures of the crystals that I got from any of these solutions, if it might help identify. My plan is to just keep an eye on them. Mohr's salt is stable on air, so I'll watch to see if it degrades over time.

Edit: I noticed the crystals turning brown so clearly I only got iron (ii) sulfate and it's oxidizing to iron (iii) sulfate. I redissolved them in about 25% sulfuric acid and I'm going to recrystallize. To be fair the procedure for the method I used wasn't super clear.


texts: Why is there a lone pair in thionyl fluoride?

texts:
Why is there a lone pair in $\ce{SOF2}$? I drew its structure, which according to me should look like this:

Why is there a lone pair on sulfur? Isn't its octet complete? If yes, why should it expand its octet and gain more electrons?


texts: Why trans-1-chloro-4-methylcyclohexane have a higher relative energy than trans-1-chloro-2-methylcyclohexane?

texts:
Both can be A,a or e,e, in 1,4 the groups are further apart -> less steric strain, why is 1,4 less stable according to experimental values?
1,2 high energy conformer's relative energy (kj/mol) is 4.05 and
1,4 high energy conformer's relative energy (kj/mol) is 4.50


texts: When recharging a lead-acid battery, how are the terminals of the battery connected to the voltage source. I mean, do we connect the positive terminal of the battery to the negative terminal of the source and vice versa? Or does the positive go with the positive and the negative with the negative? Also, are the electrodes reversed while the battery is being recharged?


texts: Contribution of Tetrahedral and Octahedral voids in HCP

texts:
I cannot find anywhere what the contribution of atoms situated at octahedral or tetrahedral voids in a HCP unit cell would be. I need to know this to be able to calculate the formula of a compound with HCP unit cell, when the positions of the atoms in the lattice are given.
What I mean by 'contribution' is how much of the atom in that lattice point belongs to one unit cell. Eg:- in CCP packing the contribution of atoms at the corners is 1/8 th.
I know that in a CCP unit cell the octahedral voids are there at the body center and the edge centers- so the contribution of an atom from both locations is different- 1 and 1/4 th. So I'm not sure whether the positions of OTs or TVs in a hcp unit cell are different (for the atoms of the same type) if so could someone tell how the contribution would be?


texts: In a character table one can find the reducible representation of vibration of a molecule. In such a table we also see things like $xy,z,x...$. If this corresponds with an irrep we say that IR transitions can occur if $x,y,z$ and quadratic terms give Raman transitions. This is because the dipole moment and polarizability are non-zero and can change in that case. My question is: where does this come from? I prefer a physical or mathematical answer involving quantum mechanics since I am from physics.


texts: Why zinc sulphate solubility is higher in ethylene glycol than water?

texts:
I'm trying to find saturation point for dissolved zinc sulphate in water and ethylene glycol.

Based on my knowledge, water is more polar than ethylene glycol as reflected in its higher dielectric constant value. However, max solubity of this salt in water is roughly limited to 3M and for ethylene glycol is much higher (experiment in progress to determine the right number).

What causes this opposite behaviour ?


texts:
Recently, while reading about isomers I learned that cis isomers are more stable than trans isomers.

I referred many books as well as searched around the internet but I didn't find a suitable explanation.

Could someone please explain this to me?


texts: Where can I access H. Landolt's article/book on his Iodine Clock experiments?

texts: I simply want to take a look at Landolt's original writings and data so that I can make notes and reference it for a report I'm writing. I've looked everywhere on Google and I can't find anything other than articles that cite his work. It would be a great help if I can find a translated copy in a digital format.


texts: What is the reasoning behind the increasing pKa for organic compounds?

texts:
Arrange the following according to increasing $\mathrm{p}K_a$.

Cyclohexanol
Phenol
Cyclohexane carboxylic acid

Please tell me the logic along with the solution.
I am confused between phenol and cyclohexanol because i guess phenol is resonance stabilized-the phenoxide ion


texts: Classically permitted position values in a quantum harmonic oscillator

texts: In  a quantum harmonic oscillator that is in the state with quantum number $n$, what range of the position $x$ is allowed classically? Does it have something to do with Bohr's correspondence principle?


texts: Writing atoms of functional group backwards

texts: Can the $\ce{HO}$ bond be written as $\ce{OH}$ and still be correct?


texts: Group theoretical condition for an integral to be zero

texts:
In many aspects of chemistry it is of interest to find out whether a given integral $\int \psi \,\mathrm{d}\tau$ vanishes, i.e. becomes zero. Group theory provides us with a handy condition:

  If $\Gamma_\psi$ does not include the totally symmetric irreducible representation (TSIR) of the point group, then $\int \psi \, \mathrm{d}\tau$ must be equal to zero by symmetry.

The utility of this is that it can be easily expanded to different types of integrals, such as matrix elements $\langle i | A | j \rangle$, where the integrand transforms as $\Gamma_i \otimes \Gamma_A \otimes \Gamma_j$. If the direct product does not contain the TSIR, then the matrix element must be zero.

What is the theoretical basis of this statement, i.e. is there a proof of it?

In particular I'd like to see a proof that:

doesn't make assumptions about which symmetry operator(s) the integrand is not symmetric under; and
is able to deal with irreps with dimensionality larger than one.

But if such a proof doesn't exist, I'd be happy to compromise on one or both of these criteria.

I checked FA Cotton's book, but he skirts the issue by saying that "it is a generalisation of the case where $\int y(x)\,\mathrm{d}x = 0$ if $y$ is an odd function of $x$" (p 107, 3rd ed.). That does makes sense, and I have an idea of how it could be mathematically formalised, but it doesn't satisfy either of the two criteria above.


texts: Entropy paradox and Confusion with Gibbs energy

texts:
Define $G=H-TS_\text{sys}$. Then,
\begin{align}
\mathrm dG &=\mathrm dH-S_\text{sys}\,\mathrm dT-T\,\mathrm dS_\text{sys}\\[3pt]
&=-T\left(\frac{-\mathrm dH}T+\mathrm dS_\text{sys}+S_\text{sys}\,\frac{\mathrm dT}T\right)
\end{align}
At conditions of constant temperature and pressure, $\frac{-\mathrm dH}T=\mathrm dS_\text{surr}$ and $\mathrm dT=0$. Thus, we end up with:
$$\mathrm dG=-T(\mathrm dS_\text{sys}+\mathrm dS_\text{surr})=-T(\mathrm dS_\text{universe})\tag{E-01}$$
Using $H=U+pV$, and by using the first law of thermodynamics, it can be shown that:
$$\mathrm dG=V\,\mathrm dp-S\,\mathrm dT$$
At constant $p,T$, this equation reduces to $\mathrm dG=0$. Using this in $\text{E-01}$ yields $\mathrm dG=\mathrm dS_\text{universe}=0$, at constant $T$ and $p$.
So how exactly do we obtain the so-called "spontaneous processes", which have a negative value of $\mathrm dG$ at constant $T$ and $p$?
I can somewhat see why the result makes some sense: The conditions assumed in the derivation resemble a reversible thermodynamic process, for which it's known that $\mathrm dS_\text{universe}$ is zero. The question in bold though is still unanswered. Maybe I am confused regarding what is actually meant by $\Delta G$.


texts: What makes many water soluble fertilizers blue?

texts: I've noticed that water soluble fertilizers tend to be blue. What chemicals or chemical reactions cause this color here? Is this necessary or for aesthetic purposes? I haven't seen this in organic fertilizers. I figured chemists might be able to examine the ingredients of Miracle Gro or something and tell me. I'm guessing it has something to do with copper.


texts: Protonation of compounds with two or three neighboring nitrogens

texts:
I am working with organic compounds. Many of them are similar to this ones:

The R group (which I paste for completeness) is:

I am a bit confused about the protonation state of those amine-compounds at pH=7.4, in aqueous solution.

N-substitued amines are more basic than the other ones. For example methylamine is more basic than ammonia.
But the protonation state of the ring is more complex than that, and I can't understand how to protonate it.

I suppose that in a kind of analogy with the guanidine (product) we could protonate again the double bonded nitrogen (imine).

Will amine be protonated? Will that compound has $+2$ charge?

Guanidine

It will possibly be protonated in the double bounded nitrogen, because it has more negative density charge and resonation is not broken. Any other point of view will be welcome.


texts: Litmus paper - turning red, blue and even bleached

texts:
I have blue litmus paper, and if I put it in an acid it turns red. I also have red litmus paper, and if I put it in a base, it turns blue.
I know the question about litmus was asked and answered and I like the answer:
How does the litmus pH indicator work?
However, damp litmus paper also becomes bleached in presence of chlorine gas. I believe it has nothing to do with the mechanism described in aforementioned question. I wonder what the mechanism is. Wikipedia actually suggests:

  For instance, chlorine gas turns blue litmus paper white – the litmus dye is bleached, because of presence of hypochlorite ions. This reaction is irreversible, so the litmus is not acting as an indicator in this situation.

I also found an equation which describes formation of hypochloric acid (source):
$$\ce{Cl2 (g) + H2O (l) -> HClO (aq) + HCl (aq)}$$

The problem that I have now is as follows: We know that litmus paper gets discolored because of contact with hypochloric acid. But what is actually the chemical reaction for that?


texts: I need to identify separation processes that begin with each letter of the alphabet. I am missing an example for B, J, K, O, Q, X, Y, and Z. Any help will be greatly appreciated. Thank you.


texts:
IUPAC Red Book in section IR-4.4.4 Ligand abbreviations [1, p. 63] states the following:

  N.B. Abbreviations for solvents that behave as ligands should also be in lower case letters [e.g. dmso for dimethyl sulfoxide {(methylsulﬁnyl)methane}, thf for tetrahydrofuran]; the practice of capitalizing the abbreviation of a solvent when it does not behave as a ligand is strongly discouraged as an unnecessary distinction.

To my understanding, applying this rule to, lets say, $\ce{[CrCl2(C2H6OS)4]Cl * C2H6OS}$ complex [2] as example, leads to the following (correct me if I'm wrong):

\begin{array}{ll}
\ce{[CrCl2(DMSO)4]Cl * DMSO} & \color{red}{\text{wrong}} \\
\ce{[CrCl2(DMSO)4]Cl * dmso} & \color{red}{\text{wrong}} \\
\ce{[CrCl2(dmso)4]Cl * DMSO} & \color{red}{\text{wrong}} \\
\ce{[CrCl2(dmso)4]Cl * dmso} & \color{green}{\text{right}} \\
\end{array}

In the other hand, we are used to solvent abbreviations being capitalized, e.g. ACS Style Guide suggests abbreviating dimethyl sulfoxide as DMSO and it seems like it doesn't make any distinction between the ligand form and the free form [3, p. 177]:

  DMSO $\qquad$ dimethyl sulfoxide (also $\ce{Me2SO}$)

Does the rule from IUPAC Red Book also mean that when using in text (e.g. referring to a solvent as to reaction media) "dmso" is preferred over "DMSO", or this rule is only applicable when solvent acts as a ligand and/or solvate?

Bonus question: If both ways of capitalization are possible, then when creating list of abbreviations (e.g. using glossaries package with $\LaTeX$), do I need to separately list DMSO and dmso? If not, which one should I pick?

References

IUPAC “Red Book” Nomenclature of Inorganic Chemistry; Connelly, N. G., Royal Society of Chemistry (Great Britain), International Union of Pure and Applied Chemistry, Eds.; IUPAC Recommendations; Royal Society of Chemistry Publishing/IUPAC: Cambridge, UK, 2005.
Al-Najjar, N. A.; Al-Sudani, A.-R. H.; Shanshal, M. A.; Mousa, F. H.; Kariuki, B. M. Acta Cryst E 2013, 69 (7), m395–m396 DOI: 10.1107/S160053681301622X.
The ACS Style Guide: Effective Communication of Scientific Information, 3rd ed.; Coghill, A. M., Garson, L. R., Eds.; American Chemical Society; Oxford University Press: Washington, DC; Oxford; New York, 2006. DOI: 10.1021/bk-2006-STYG.fw001.


texts:
I've been thaught that water at 1 atm water boils at 100 °C (the so called “normal boiling point”).

However, I came across a more rigorous description of the boiling process saying that in order to fulfill thermodynamic equilibrium between liquid and vapour the pressure inside the bubble must be higher than that outside and accordingly the liquid results superheated (to be at the same temperature of the vapour).

I also understand the nucleation process, but here for sake of simplicity I assume that the bubble is already present.

So my question is why we say that water boils at 100 °C (at 1 atm)?


texts: IBrF2 - van der Waals repulsions - and number of unique bond angles

texts:
I understand that the molecule $\ce{IBrF2}$ is T-shaped, with three ligand atoms and two non-bonding pairs.

However, how many unique bond angles can this molecule exhibit?

My professor argues for the existence of only 2 unique bond angles in this molecule, with the somewhat $< 180^\circ$ axial $\ce{F-I-F}$ bond angle and the two equivalent and somewhat $< 90^\circ$ $\ce{F-I-Br}$ bond angles.

However, can't we also arrange this molecule as to have this axial arrangement of atoms: $\ce{Br-I-F}$?

My professor argues that this arrangement is impossible due to van der Waals repulsions. I suppose this makes sense; the two lone-pairs $\ce{<->}$ large bromine atom repulsions would make this shape unfavorable.

Impossible? I'm not sure about that. Dammit, nothing in chemistry is impossible.

What do you think? I'm arguing for the existence of either two or three bond angles because we can either have a $\ce{F-I-F}$ axial arrangement or a $\ce{Br-I-F}$ axial arrangement. Plus, axial bonds are longer than equatorial bonds. So that would lower the energy of the $\ce{Br-I-F}$ axial conformer. Side note: why are axial bonds longer than equatorial bonds?

In sum:


texts: Is hydrogen peroxide safe for cleaning porcelain?

texts:
From my understanding hydrogen peroxide only reacts with bacteria in a way that it should burn them more or less.

If that is true, can I then safely use hydrogen peroxide to clean my bathroom sink which are made of porcelain?


texts: EPR or NMR sample that will give narrow lines at 4 K

texts:
We have made a crossed coil setup (X and Y transmit/receiving coils) with a SQUID pick up loop along Z.

Now we want to see EPR or NMR lines, probably using it in a CW fashion, ie. putting a ramp + lock-in oscillation in X, a CW excitation frequency in Y and demodulating the SQUID signal in Z.

Question is: What sample will give us nice, narrow, distinguishable lines at 4°K?.

Note: we can only go up to 10 mT with the X coil. Liquid $^3$He is off our budget.


texts:
When dealing with organic reactions, heating under reflux is often required, such as the oxidation of Toluene using acidified $\ce{KMnO4}$ and dilute $\ce{H2SO4}$ to Benzoic acid($\ce{C6H6O2})$

What does this mean and how does it differ from "normal" heating?


texts: In a neutral atom, can neutrons be ejected, and if so, by what (nuclear) process or reaction? I have read Neutron emission and Can a proton be ejected from an atom, but I don't understand how and if that would work for removing neutrons from a heavy atom such as lead-208. Can neutrons be ejected from lead-208 so that it is lead-197, and if not, why?


texts:
I was just wondering which overlap is stronger, 2s-3p or 3s-2p? I believe this can probably be explained by involving some sort of mathematics (?) which I haven't used yet.

Edit: Note that 2s-3p refers to the overlap of 2s of one atom and 3p of another atom. Similarly for 3s-2p.

I haven't really come across an example for this case, guessing it's hypothetical. It'd be great if someone could give actual examples too if they exist.


texts: Aluminium sulphate solubility as function of the pH

texts:
earlier I asked about how to know the aluminium sulfate solubility as function of the ph (see the previous question here). I found this diagram on the page 57 of

  Rubin, A. J., & Hayden, P. L. (1973). Studies on the Hydrolysis and
  Precipitation of Aluminum (III).

But I'm a little confused about the interpretation. Is the
$\mathrm{Al_{2}(SO_{4})_{3}}$ insoluble between pH 5 and 7?. What will be the correct interpretation of this diagram?


texts: What kind of isomerism does Ni(PPh3)2Cl2 have and what is their IUPAC name?

texts: I know that there are 2 isomers that $\ce{Ni(PPh3)2Cl2}$ have and they exist in equilibrium. I am tempted to name them cis- and trans- but it does not sound right.


texts: What are the GDB-13 criteria for "synthetically accessible organic molecules"?

texts:
I'm trying to understand the QM datasets (QM7, QM8, QM9), however, in the description of QM7 the data is described as follows:

  [The] QM7 dataset, which is a subset of GDB-13 (a database of nearly 1 billion stable and synthetically accessible organic molecules) containing up to 7 heavy atoms C, N, O, and S. The 3D Cartesian coordinates of the most stable conformations and their atomization energies were determined using ab-initio density functional theory (PBE0/tier2 basis set)

What exactly does the phrase "stable and synthetically accessible organic molecules" mean? If I had to guess I would have said it means they can be synthesized in a lab, but I didn't want to guess.


texts:
Is there an example of two reactions that catalyze one another? More than two is also helpful, but I guess it will be hard to find one.

By "catalyze one another", I mean that one of the products of the first reaction acts as a catalyst for the second reaction.


texts: Would Chlorine or Chloramine gas show up on a VOC test?  My apartment was cleaned using chlorox and lysol, and there has been a smell that's been lingering for about 10 days.  The air was tested with a VOC meter but nothing came up.  Would Chlorine and Chloramine have shown up on this test?


texts:
I don't quite understand what is meant by the Helmholtz double layer.
Textbooks states something along the lines of:

  the colloidal particles attain charge by selective adsorption, due to
  this it attracts a layer of opposite charge,this layer is called the
  Helmholtz double layer and the potential between them is called Zeta Potential

What stops the oppositely charged layers from combining (neutralizing) with each other?


texts: Computational program not using full cpu power

texts:
I started some computations on Gamess.

For instance, when I compute the frequencies of an optimized structure, I see in the terminal that the job only uses 40% of the CPU core most of time (sometimes it goes to 100%). When I decide to provide 2 cores for the job, it only uses something like 20-25% of each core most of the time (and sometimes 100% of each core too). Why would not the task take maximum power to achieve the computations ?


texts: Resonance and reductions with sodium borohydride

texts:
I know that sodium borohydride doesn't work particularly well on resonance-stabilized carbonyl groups (i.e. esters) but what about this carbonyl in the center of the above picture? This appears to be somewhat resonance-stabilized ... why would sodium borohydride still work  here? Sodium borohydride is a nucleophilic reagent. On the other hand the second resonance contributor I've drawn is pretty crappy; yes - it's part of an aromatic system - but it's also a carbocation. And the R' group is inductively donating (although I suspect this is a fairly minor point).

Or does it just work in the above synthesis but not with a yield comparable to something such as sodium borohydride and formaldehyde?


texts:
I wonder, what happens when sodium reacts with alcohol? What is the reaction mechanism?
I think that sodium is an electrophile that attacks the nucleophile oxygen atom in the -OH-group of the alcohol. Sodium will take one electron and bond with the oxygen molecule, while the bond between the oxygen and hydrogen will break. Am I correct?


texts: Should the coupling between vibrational modes increase or decrease with increasing temperature/vibrational energy level?

texts:
At low temperatures, the amplitude of vibrations should be smaller, so the vibrations should be as harmonic as they are ever going to be. Thus, the normal mode description of vibrations should be at its best at low temperatures.

As this paper [1] describes, the normal mode description must be wrong when the vibrations reach an amplitude such that a bond is broken. Namely, if you consider the symmetric stretch of a molecule benzene, the normal mode coordinate moves all $\ce{C-H}$ bonds in unison so that they all pass through their minimum simultaneously. Yet, it is extremely unlikely that all of these bonds will break simultaneously. Much more likely is that only one bond breaks. Thus, the authors advocate the use of the local mode description of vibrations in high vibrational energy levels. Personally, I like the local mode description in most cases because it includes anharmonicity quite naturally. It has two shortcomings, however. It is only good for vibrations between a light and heavy atom ($\ce{X-H}$ generally). Second, it explicitly ignores coupling between modes by treating each vibration as that of a diatomic.

Both normal modes and local modes fail to capture any real coupling between vibrational modes, but it seems that the high-temperature limit is for the modes to behave as local modes. This seems to be in conflict with what I have heard on multiple occasions that the coupling between modes should increase as temperature increases. The temperature doesn't really matter, I'm just saying as you thermally populate higher vibrational states, what happens to the coupling.

Now, the final thing is that I believe there is ambiguity in what we mean by coupling between modes and this is probably the source of my confusion. When I say coupling, it could mean how well I am able to write each vibrationa using independent coordinates. That is, the potential energy of a particular oscillator is a function of one coordinate only. As temperature increases, does this approximation become better or worse?

The second meaning of coupling between modes could be how easily energy is redistributed between vibrational modes. I would think this and the previous point are related, but I believe the only condition for having energy redistributed between vibrational modes is that the vibrations are anharmonic. Not necessarily that they are coupled in the sense as above.

I believe that people mean each of these things when talking about coupling between modes even though they are distinct concepts. What is the right way of talking about coupling?

To summarize:

As higher vibrational energy levels are populated, does the assumption of each vibration depending on one coordinate only become better or worse?

As higher vibrational energy levels are populated, is energy redistributed between modes more easily or less easily, and does this relate to the first question at all?

Disclaimer:
I'm fairly certain energy redistribution should become faster at higher temperature as vibrations will become more anharmonic.

[1] Henry, B. R. (1977). Use of local modes in the description of highly vibrationally excited molecules. Accounts of Chemical Research, 10(6), 207-213.


texts: Term used to describe scalar coupling over a single bond?

texts: I know that coupling on NMR over two bonds is referred to as geminal coupling and over three bonds is referred to as vicinal coupling. However is there a term for coupling over one bond (such as a carbon-13 bonded to a fluorine?


texts: Skin adhesive that can be used daily without damaging skin

texts: What is the branch of chemistry that deals with skin adhesives? Is there an adhesive that is not water soluble that is safe to use every day?


texts: What is the maximum molarity of aqueous HCl?

texts:
Here is a problem a made up:

  We have some aqueous $\ce{HCl}$. What is the maximum possible molarity of the $\ce{HCl}$?

How do I solve this? I don't have any good ideas.


texts:
How should I determine the total number of phases that are at equilibrium with each other in a multi-component mixture?
For example, this problem is from the 2007 GRE published by ETS (Problem 24):

What is the maximum number of phases that can be at equilibrium with each other in a three component mixture?

I initially thought the answer should be 3 since no matter what kind of mixture it is there should always be solid, liquid, and gas. But then I understood that there can be situations like immiscible liquids which increases the total number of phases. The actual answer is 5. What does this number entail?


texts: Why does baking soda and vinegar remove stains?

texts:
To remove a stain on fabric, I often rub baking soda into the stain, and then sponge it with white vinegar. This causes a chemical reaction, involving some fizzing and frothing, and once the fabric has dried, the stain (hopefully) has disappeared. Why does this chemical reaction remove the stain?

From my basic knowledge of chemistry, I know this is a classic Acid + Base -> CO2 + H2O + Others. But this doesn't involve the chemicals which have caused the stain.

Is it that these chemicals also react, and turn into other colourless products? Or is it that the frothing action from the reaction just dislodges these chemicals, allowing them to more easily be wiped clean? Or is there another answer?


texts: I've been studying photosynthesis and something made me think about how chlorophyll itself is made in plants.How exactly is it formed ?


texts: Do hydrogen atoms not bound to carbon also appear in 1H NMR spectra?

texts: I would like to know if hydrogens that are not bound to a carbon (such as in groups $\ce{-OH}$ and $\ce{-NH2}$) would lead to the presence of a singlet peaks in the NMR spectra or not, and if we have to count or omit them in the integration of the spectrum. I thought I was sure about it but lately I noticed that it depends on the spectra.


texts: Python package for modelling chemical reactions

texts:
I'm looking for a package that is compatible with Python 3 and can actually do work with reactions along with, for instance, referencing values. Ideally, it should also not be a package that will take 20 days to learn how to access one value.

More specifically: there should be a way to figure out all possible reactions a certain state could lead to, a way to manipulate lists of possible reactions and applicable reactions in certain states, and to apply reactions to states to get a resulting new state (this, of course, may require some coding on my part, but just an idea of what it should lead too - the more the package can do the better).

Thanks; I'd be glad to provide any clarification in the comments.


texts: Can 4-pyridones be synthesised analogously to 2-pyridones?

texts: I understand that 2-pyridone derivatives can be synthesized by oxidizing an N-methyl pyridinium salt with $\ce{[Fe(CN)6]^3-}$ under basic conditions. Can a similar method be used to produce 4-pyridones ?


texts:
Which of the following alkenes would produce two products when they undergo an addition reaction with hydrogen bromide?

Ethene
But-1-ene
But-2-ene
Hex-3-ene

The correct answer (according to my textbook) is But-1-ene but I do not understand why this is.


texts: Why do enthalpy changes of combustion and formation not take into account oxygen?

texts:
I've seen many enthalpy changes in my studies and I don't understand why the oxygens on either side of reactions are not calculated (especially if the unreacted oxygens don't balance). For example:

$$\ce{2C(s, graphite) + 3H2(g) + 1/2O2(g) ->  C2H5OH(l)}$$


texts: Why are enthalpy of combustion and molar mass of organic compounds proportional?

texts:
I noticed that when you graph heat of combustion against molar mass, you get a completely straight line with a correlation of 1. I know that the longer the chain is, the stronger the LDF get, so it is expected to see an increase in heat of combustion if molar mass increases. Though, I don't know why the curve is completely straight.
You can see heat of combustion against molar mass of alkanes in the graph below.

Data source: Organic Compounds: Physical and Thermochemical Data


texts: Why do things want to lower their energy?

texts:
Like if we consider a container of gas molecules as a system, Why does it want to lower its energy?

I have read that always more spontaneous events are favored. So Gibb's Free energy should have a negative value i.e ΔG=ΔH-TΔS<0. So Entropy Contributes towards more spontaneity. But Randomness contributes towards more entropy and having more Internal energy causes more random motion.
So overall more energy should contribute towards more Spontaneity which is favored in nature. But we observe that things tend to lower their energy. Please Explain.

Edit: Well I guess I might have found the answer -
When a system lowers its energy, ΔH becomes negative ( due to it being exothermic) so at moderate temperatures, the entropy contributes to lower spontaneity but ΔH is more negative so ΔG becomes more negative(more spontaneous). While at high temperatures, endothermic processes are favored (ΔH positive)
Thermodynamics is so beautiful!


texts: What is a stereochemically active or inactive s orbital?

texts:
In Concise Inorganic Chemistry by JD Lee (4th edition; adapted by Sudarshan Guha), page 73 under the section 3.6 (VSEPR Theory chapter Chemical Bonding):

...according to this theory, the position of the lone pair in $\ce{XeF6}$ molecule should be in axial position and the shape should be pentagonal pyramidal. But this is not observed and the actual shape of molecule is octahedral. This implies that the lone pair is placed at equatorial position, and this explains the structure of $\ce{XeF6}$ shown in figures 3.7 a,b,c.
According to Figure 3.7, $\mu_\text{expected}$ for $\ce{XeF6}$ is not equal to zero. But $\mu_\text{real}(\ce{XeF6})\sim0$ . To explain the above facts, it is considered that the actual molecule is in dynamic equilibrium of all the three structures shown in Figure 3.7. Here it is considered that the lone pair is present in the stereochemically active $s$ orbital and similar structure is observed as $\ce{IF6-}$. But anions like $[\ce{SbX6}]^{3-}$, $[\ce{TeX6}]^{2-}$ ($\ce{X}=\ce{Cl, Br, I}$), $[\ce{BrF6}]^-$,$[\ce{ICl6}]^-$ have been assigned perfectly octahedral structure on the basis of X-ray crystallography and the lone pair is present in stereochemically inactive $s$ orbital.

To explain the dipole moment, it is considered that the molecule is in dynamic equilibrium between three structures, where it is considered that the lone pair is present in the stereochemically active s orbital. However, I don't get what the author means by stereochemically active (or inactive) s orbital.


texts: IUPAC way of writing prefix of alkyl isomers of an ether

texts:
Consider this compound:

I am able to identify the base chain as propane. But, I am having trouble naming the other side of the chain. Will it be named as:

2-(isopropoxy)propane,
2-[(propan-2-yl)oxy]propane, or,
2-(2-propoxy)propane

What is the preferred IUPAC way for such a naming of isomeric alkyl groups?


texts: What are the differences between the various household surfactants?

texts:
In a typical household, the following surfactants are found, among others:

Soap / handwash
Shower gel
Shampoo
Dishwashing agent
Washing powder / liquid

From my understanding, the role of all these is to lower the surface tension between water and fatty acids, enabling one to "wash" things.

Are they all the same then, and is the only difference between them marketing? Can I wash my hair with dishwashing agent, or pour shower gel into my washing machine?


texts:
An acyl group is defined as being a result of removing a hydroxyl group from an oxoacid. This is supposed to result in a group of the form R-C=O. An oxoacid, in turn, is defined as an acid which contains oxygen.
I assume an oxoacid must have a hydroxyl group, in order to be able to donate a proton and be considered an acid. But why would this result in a group of the form R-C=O?
The part which I find mysterious, to be precise, is the carbon atom: where does it come from in oxoacids that do not contain carbon?
Sulfur oxoacids, for instance, are a whole group of acids that do not contain carbon, at all. How do you end up with R-C=O if you remove a hydroxyl group from disulfuric acid, for instance?
Also, what if there is carbon, e.g. a group of the form R-C-OH, where the R does not contain any oxygen atoms with a double bond? If you remove the hydroxyl group, why would you have to end up with an oxygen with a double bond?


texts: This question just popped in my head as I was working with electric force problems involving atoms. Why is the amount in a mole equal to the Avogadro's number? Do atoms/molecules/etc. tend to group in this exact amount? Why do we use this number as a unit of measurement?