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.
3,140
questions
4
votes
0answers
6 views
Is there a rule of thumb to predict when coupled cluster might dip below the variational limit?
Coupled cluster is a non-variational method, meaning that it can give energies that are below the true FCI energy (the "variational limit" for variational methods).
Often coupled cluster still gives ...
0
votes
1answer
48 views
Is the rate of electrolysis the same throughout as long as voltage is same
In an electrolytic cell, where the electrolysis of dilute sulfuric acid is taking place, would the rate of electrolysis be constant always, even at the beginning?
By rate of electrolysis, I mean the ...
0
votes
0answers
24 views
Vapor pressure and Ideal Gas Law
Given the ideal gas law and it's plot of Volume vs Pressure, how does a substance's vapor pressure affect this plot? Does it cause the graph to plateau somewhere? If so why does this happen?
1
vote
0answers
21 views
What could be causing a small uptick in FCS curve at approximately 10 microseconds
I work as an RA in an academic lab. I've been working with FCS fitting for an experiment, and took FCS curves for fluorescein and calmodulin, displayed with residuals below:
]2
I fitted both to an ...
0
votes
0answers
27 views
Calculating pH of rain water
The concentration of $\ce{SO2}$ in the atmosphere over a city on a certain day is $\pu{10 ppm}$. Given that solubility of $\ce{SO2}$ in water is $\pu{1.3653 mol L-1}$ and $\mathrm{p}K_\mathrm{a}$ of $\...
8
votes
2answers
151 views
Why is it necessary to consider infinitesimal changes in p,V,T for H,U and G given that they're state functions?
State functions such as $G$ only depend on the state of the system and are not dependent on the "path" that took the system to that state (which would be the case for work, for example, which is not a ...
0
votes
0answers
4 views
Stoichiometry in rate law [closed]
When are the stoichiometric coefficients equal to the exponents of concentration in rate law r=k[a]^m?
6
votes
1answer
114 views
Basic thermodynamics question about work
I am getting into thermodynamics, and I have a basic fundamental question about the definition of the change in internal energy $\mathrm{d}U$:
$\mathrm{d}U = T\,\mathrm{d}S - P\,\mathrm{d}V + \sum\...
2
votes
3answers
108 views
Degree of dissociation of weak electrolyte at infinite dilution
Why the degree of dissociation of weak electrolyte is 1 at infinite dilution and how do we get the result? Like I know that at infinite dilution the concentration of solution is 0 but what does that ...
2
votes
0answers
18 views
Greater ligand stabilization of the lower oxidation state increasing redox potential
According to Atkins, P.W., De Paula, J. and Keeler, J., 2006, Atkins' Physical Chemistry,
$$
\begin{align}
\ce{[Fe(CN)6]^3- + e- &<=> [Fe(CN)6]^4-} &\quad E^\circ &= \pu{+0.36 V} \...
1
vote
3answers
94 views
In an isothermal process, how can the change in internal energy be 0?
It was written in my textbook,
$$
\mathrm{d}U =
\left(\frac{\partial U}{\partial T}\right)_V \mathrm{d}T
+\left(\frac{\partial U}{\partial V}\right)_T \mathrm{d}V
$$
If the process is isothermal,...
0
votes
2answers
32 views
Clarification required on whether to use $C_v$ or $C_p$ in this question on finding entropy change
$1 \text{ mol}$ of an ideal monoatomic gas at $300 \text{ K}$ is subjected to a reversible isentropic compression process until final temperature reaches $600 \text{ K}$. If initial pressure is $1 \...
0
votes
0answers
34 views
Hartree-Fock vs. DFT vs. Hohenberg-Kohn vs. Kohn-Sham
What is the difference between these four approaches?
My current understanding is that Hartree-Fock uses only 1 slater-determine (accounting for antisymmetry) but neglects correlation between ...
3
votes
1answer
79 views
Which solvent is good for using SU-8 particle in Optical tweezers?
I'm studying Optical tweezers. I've used Polystyrene for samples. Nowadays, I've got SU-8 pillar. I wanna use that for sample, but its density is heavier than water. I can't use that. So I wanna know ...
5
votes
1answer
96 views
What are the disadvantages of using the InChI format?
What are the disadvantages (if any) in producing and using the InChI format of chemical compound representation in chemoinformatics? Are there any particular problem one can face when using InChI?
-2
votes
1answer
39 views
Difference between equations for spectroscopy wavenumbers
What is the difference between these two equations and when is appropriate to use which one?
We were told that $F(J)$ in this case is
$F(J)= E/h$ for units in frequency
And
$F(J) = BJ(J+1)$
$\...
0
votes
0answers
24 views
Rotational spectroscopy application of different equations [duplicate]
So we were given two problems and I don't understand why one was solved one way, and another was solved another way
Estimate the bond length of 12C16O (pure rotational spectrum) given J''=3 (15.356 ...
3
votes
0answers
24 views
Tight binding model with Extended Huckel Approximation
I've been reading Albright's Orbital Interactions in Chemistry. In the chapter on solids, he provided a general approach to find the band structure of a solid state system
Now if we are to model a ...
5
votes
2answers
6k views
Why does a hard-boiled egg have more entropy than a normal egg?
The question "Why does a hard-boiled egg have more entropy than a normal egg?" was recently asked on one of my tests.
I said that entropy will decrease as a hard boiled egg has molecules in a more ...
32
votes
5answers
19k views
What roles do neutrons play in an atom?
An atom typically consists of electrons, protons, and neutrons. Electrons are negatively charged and participate in bonding to stabilize the atom.
Conversely, protons are positively charged and ...
1
vote
1answer
34 views
Electrochemistry conditions for voltage to increase in a galvanic cell
I understand that increasing the concentration of reactants in a galvanic cell generally causes the voltage of the cell to increase. But is that really the case always?
Consider a standard cell of ...
3
votes
0answers
38 views
Tight binding model for nanoparticles as finite systems
I'm still trying to calculate the band structure ab initio for some hypothetical nanoparticles. It seems that I can directly build a tight-binding model by forming Bloch functions, numerically ...
0
votes
0answers
14 views
Magnitude of Coulombic integral of atomic orbitals
I'm wondering anyone knows what's the typical magnitude for Coulombic integral of atomic orbitals in large molecules (not simple diatomics). Also, is it right to say that the integral has a greater ...
1
vote
0answers
29 views
Methylhydrazine Calorimetry
Below is a chemistry practice problem. I am curious why the change in heat of the oxygen molecules doesn't affect the calculations.
Methylhydrazine ($\ce{CH6N2}$) is commonly used as a liquid ...
1
vote
1answer
54 views
Rotational Energy Levels
Why does the rotational constant B decrease and transition spacings decrease as the mass of a particle increase?
I understand from a purely equation perspective that since
$$B = \frac{h} {8\pi ^2 ...
-1
votes
0answers
17 views
Outline the steps involved in the Hartree–Fock method for the calculation of molecular electronic structure [duplicate]
I understand that the steps of the self-consistent method are as follows:
guess the form of Psi(r)
use psi(r) to evaluate for V1eff(r1) then solve for a new psi(r)
the two wavefunctions tend to ...
13
votes
3answers
878 views
Ellingham Diagram
My textbook says the following about the Ellingham diagram:
Each plot is a straight line except when some change in phase ($\ce{s -> liq}$ or $\ce{liq -> g}$) takes place. The temperature at ...
1
vote
0answers
13 views
Inductively Coupled Plasma and Mass Spectrometry
I was doing some homework and I was reading about how ICP is suitable for mass spectrometry and it said how its high temperature favours ionization which is good in MS. But also, because the ...
1
vote
1answer
83 views
Difference between Particle in a Box and Harmonic Oscillator approximations
Why in the particle in a box model do the values of n begin at 1 but in the harmonic oscillator they begin at 0? I understand what the wave-functions and their corresponding probabilities look like ...
2
votes
2answers
92 views
Why when deriving the Clapeyron equation can you assume that dH = dq, as surely the pressure is not constant?
Part of the Clapeyron equation involves replacing $\Delta S$ with $\Delta H/T$. I can see the step from $\Delta S$ to $\Delta q/T$ but I'm not sure why you can replace $\Delta q$ with $\Delta H$. From ...
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votes
0answers
28 views
Does H2C=C=C=CH2 lie in the same plane? [closed]
explain in terms of bonding theory why all atoms H2C=C=C=CH2 must lie in the same plane
-1
votes
1answer
23 views
Calculating partial pressure with 3 equilibrium equations [closed]
So my friend had sent this question to me some days ago and it seems I still am not able to solve it. I am confused whether the amount of A that dissociates in the first equation would account for the ...
-1
votes
0answers
8 views
Atomic structure what is binding and ionisation energy [closed]
What is the difference between ionisation energy and binding energy if not then what is similarity between them
-1
votes
0answers
16 views
Can Electronegativity be explained through QM? [closed]
Even as senior in high school, I still find chemistry quite intimidating, partly due to how vast it is and partly because I don't understand when something stated in Chemistry is experimentally ...
1
vote
1answer
33 views
Determine bond length via rotational spectroscopy
Estimate the bond length of 12C16O (pure rotational spectrum) given J''=3 (15.356 cm-1) and J'=9 (38.356)
I understand that the first step is the calculate the rotational constant. So to do this I ...
5
votes
2answers
317 views
Is the equation dG = Vdp − SdT valid only for a reversible process? Can it be applied for an irreversible one too?
In the derivation, we write:
$$
\begin{align}
G &= H - TS &\quad&\to&\quad \mathrm dG &= \mathrm dH - T\,\mathrm dS - S\,\mathrm dT \\
H &= U + pV &\quad&\to&\quad ...
0
votes
1answer
1k views
How can I calculate the percentage of dissociated dinitrogen tetroxide?
When $\pu{36.8 g}$ $\ce{N2O4(g)}$ is introduced into a 1.0-litre flask at $\pu{27 °C}$ the following equilibrium reaction occurs: $\ce{N2O4(g) <=> 2NO2(g)}$; $K_p = 0.1642~\mathrm{atm}$.
...
1
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2answers
563 views
Effects of pressure on equilibrium [closed]
Which system at equilibrium will not be influenced by a change in pressure?
$$
\begin{align}
\ce{3 O2(g) &<=> 2 O3(g)}\tag{A}\\
\ce{N2(g) + 3 H2(g) &<=> 2 NH3(g)}\tag{B}\\
\ce{...
1
vote
0answers
91 views
Order of reaction in adsorption process
(1) $\ce{PH3(g) <=>[W]PH3(adsorption)->[W]P(s) + 3/2 H2(g)}$
The decomposition of phosphine on tungsten surface at low pressure is a pseudo first order reaction. This is because the rate of ...
3
votes
1answer
52 views
The reaction rate when the rate-determining step has a back reaction
For some reason, I am reviewing general chemistry and I find that the elementary reaction for the rate-determining step (RDS) is assumed to be irreversible, that is, single arrow, in all questions ...
6
votes
1answer
456 views
What is J in the rigid rotor model?
In my class notes regarding the rigid rotor model, J is described as simply the angular momentum (replacing roe or p) and is also referred to as the angular momentum quantum number.
Are these two ...
-1
votes
0answers
27 views
What is the difference between dynamical and non-dynamical correlation and which one is accounted for in Hartree-Fock theory? [duplicate]
It is my understanding that dynamical is related to the movement of individual electrons. I don't fully understand what this means though.
Non-dynamical correlation is still very unclear from my ...
0
votes
1answer
36 views
Why can a wave-function be written as a product of 1-electron wave-functions?
Why can a wavefunction be written as a product of 1-electron wave-functions when making approximations to solve atoms other than hydrogen? (ie. helium)
We used this when solving multielectron systems ...
0
votes
0answers
25 views
Finding the wavelength of maximum absorption and Crystal Field Splitting of [Ni(H2O)6]2+
(I haven't been here for a long time, so tell me if my formatting is fine)
Given
The $\ce{[Ni(H2O)6]^2+}$ complex appears green in solution from the transmitted light. Estimate the wavelength of ...
1
vote
0answers
32 views
Can we break double bonds by using laser and heat?
If it is possible then give an example for it. That chemical reaction is in this process.
step 1: {Reactant + heat(sunlight)} gives weakened bonded product1
step 2: {product1 + laser} gives {one solid ...
1
vote
0answers
17 views
Neither Raman nor IR Active vibrational modes of water [closed]
How can we find vibration modes of water that are not in IR and Raman spectroscopy? I thought these modes creat when a transition happens between 2 modes i.e from mode to another mode.
2
votes
2answers
61 views
Relation of temperature and intensive property [closed]
I came across a question that inquired about whether there exists any intensive property of a system, that is independent of temperature and then seeks proof for the presence/absence of such ...
6
votes
0answers
74 views
Anomaly in van der Waals constants of noble gases
In van der Waals equation for a real gas, the equation is
$$\left(P + a\frac{n^2}{V^2}\right)(V - nb) = nRT$$
where $P$ is the pressure of the real gas, $n$ is the number of moles of the gas, $R$ is ...
1
vote
1answer
51 views
What all information can be gathered qualitatively from the radial distribution functions of a molecule?
Apart from knowing the radius of coordination shells and the probability of finding, is there any other thermodynamic information we can gather by looking at radial distribution functions of a ...
-1
votes
2answers
37 views
What does it mean to balance a redox reaction in acidic or basic mediums? [closed]
Until now it was clear to me what balancing a reaction was. Balancing redox reaction also make sense to me. What does it mean to balance a redox reaction in acidic or basic medium?
