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# Questions tagged [physical-chemistry]

The study of chemical systems using the laws and concepts of physics. This usually requires the techniques of thermodynamics, statistical mechanics and quantum mechanics.

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### What is the nature of chemical energy? [closed]

Is chemical energy basically stored energy? I'm not sure how to define "chemical energy" while I know many physical formulas for energy e.g. potential, movement and other. Is chemical energy an ...
2k views

### Proof that Equilibrium Constant is a Ratio of Rate Constants

I have a question about this proof that shows the relationship between the rate constant and the equilibrium constant. In this proof, the assumption is that the reaction is $(a+b)$th order in the ...
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### What is the pH of a 5M solution of hydrochloric acid?

What is the $\mathrm{pH}$ of a $\pu{5M}$ solution of hydrochloric acid? So in order to solve this, apparently all you need to do is plug it into the equation: $$\mathrm{pH} = -\log[\ce{H3O+}]$$ ...
178 views

### Solvated solids

I have a very basic question concerning solvation. If a solid (solute) was dissolved in a liquid (solvent), is the solute still in the solid state? or does it convert into another state of matter when ...
9k views

### Is the first ionization energy in oxygen slightly more than nitrogen?

Why is the first ionization energy in oxygen slightly more than nitrogen? In nitrogen: $\ce{[He] 2s^2 2p^3}$ In oxygen: $\ce{[He] 2s^2 2p^4}$ This tells me that it should be easier to remove an ...
196 views

### Gibbs Free Energy and Maximum Work

I am a high school student and my professor mentioned that the Gibbs free energy is the maximum amount of work (or useful work) that a system can do, whereas entropy is a measure of the non-available ...
450 views

### Proving RTln($a_i$) equal to non PV work done by system,where $a_i$ is activity

We know that chemical potential is defined as ${\mu}_i={\mu}_i^{standard}+RT\ln(a_i)$. Here $a_i$ is the activity of $i^\text{th}$ component of solution. In case of gases instead of $a_i$ it is $f_i$ (...
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### Why does Le Chatelier's principle not apply to pure solids and liquids?

If we had a homogeneous reaction of pure liquids only, would Le Chatelier's principle still apply ? Also, wouldn't increasing the amount of solid in a heterogeneous reaction mixture at equillibrium ...
434 views

### How can we say that one mole of a substance contains avogadro number of particles?

I just want to know, what was the procedure through which the value of one mole of a substance was considered as a an aggregate of $6.023\cdot10^{23}$ particles. Secondly, how do we calculate the ...
707 views

### When simulating spectral line broadening, which convolution is preferred?

Many computational chemistry packages permit the calculation of vibrational and electronic spectra. These spectra are obtained as a set of discrete eigenvalues however they are often convolved with ...
1k views

### Why do some gases have lower value of Z for a particular pressure?

In the above graph,the minima of the curve for methane is more than that of nitrogen. Also, for a given value of pressure, the value of $Z$ for methane is less than that of nitrogen. They seem to meet ...
995 views

### A misunderstanding about the energy profile of reactions with a catalyst involved

All of us are aware of the importance of the catalysts in bio-chemistry. For a high school learner like me, catalysts ,and therefore, enzymes play a bridge-like role that connect high school bio to ...
24k views

### Why does ZnO turn yellow when it is hot?

Why does ZnO's color become yellow when it is hot? I have read that it is because of physical properties, but I need a more elaborate explanation.
3k views

### Which materials/compounds expand in response to cold temperatures?

Which materials or compounds expand in response to cold temperatures? This material or compound should expand at a slow (but constant rate), from about 0–20 months when in the following temperature ...
5k views

### Chemical properties of isotopes

I've always heard that different isotopes of the same element have exactly the same chemical properties. But for example, I've read that some compounds which have hydrogen atoms interchanged by ...
6k views

### How to determine the empirical formula for an unknown iron oxide?

I have to determine the empirical formula of an oxide of iron which has $69.9\%$ iron and $30.1\%$ dioxygen by mass in it. I have started as follows: For our convenience we take $\pu{100 g}$ of that ...
1k views

### Why does gas particle velocity affect rate of effusion?

I understand why smaller particles have more velocity, but I don't understand what velocity has to do with rate of effusion: My reasoning is thus: Pressure is the number of impacts of particles in a ...
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### Does the Maxwell-Boltzmann distribution apply to gases only?

The Maxwell-Boltzmann distribution can be used to determine the fraction of particles with sufficient energy to react. I know that the curve applies to gaseous reactants and would like to know whether ...