All Questions
Tagged with theoretical-chemistry thermodynamics
27
questions
6
votes
1
answer
237
views
Non-Arrhenius temperature dependence of bimolecular reaction rates at very high temperatures
Once I have read that in some cases bimolecular reactions can exhibit a maximum as a function of temperature due to the short lifetime of the activated complex at very high temperatures.
At low ...
- 163
2
votes
0
answers
81
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Diffusion vs mobility and the Einstein relation
This former question is about the mobility constant $M>0$ in the Cahn-Hilliard equation. To determine the value of such a mobility for a simulation study, Kim and Sanders (2020)
use the formula
$$
...
- 193
1
vote
0
answers
55
views
Why probability for an atom is fraction for population?
In the canonical ensemble the probability of finding an atom (or molecule) in its $i$-th energy state is given by the Boltzmann factor.
This probability is interpreted as the number of microstates ...
- 766
8
votes
2
answers
581
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Practical use of the partition function in molecular simulations
In the second chapter of Understanding Molecular Simulation, Frenkel and Smit derive an equation for the partition function and the thermal average of the generic observable A, stating that these ...
3
votes
0
answers
20
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Correlating specific heat (Cp) of a substance with other substance on the basis of similar physio-chemical properties
I am modelling $\ce{H2O2}$ decomposition in ANSYS Chemkin-Pro and I have difficulty finding $C_p$ (specific heat at constant pressure) for liquid $\ce{H2O2}$ for various temperature ranges.
My ...
- 31
2
votes
0
answers
32
views
expression of apparent reaction quotient
question
When computing the Gibbs energy change of a reaction using Legendre-transformed $\Delta_fG'$ values for a given $\mathrm{pH}$, the formula of the $\Delta_rG'$ of the reaction is:
$\Delta_rG' ...
- 306
1
vote
0
answers
44
views
What makes determining entropy changes theoretically so hard compared to enthalpy?
It is really hard to determine the entropy change of a reaction accurately because of subtle solvent effects and a lack of standard entropies. On the other hand, enthalpy is relatively easy and ...
- 732
1
vote
2
answers
227
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Concept of enthalpy at a given temperature
In thermodynamics, we always quote a fixed temperature, whenever we mention enthalpy of a reaction. For instance, one can determine the enthalpy of combustion of methane at 25 °C. Now almost all ...
- 41.5k
6
votes
2
answers
325
views
Tunneling in chemical reactions
We know that quantum tunneling is the reason behind several natural phenomenon like alpha decay and thermonuclear fusion inside the stars. How can it influence chemical reactions by tunnelling a ...
6
votes
1
answer
196
views
Understanding elementary rate laws from a probability stand point
I am learning about chemical kinetics and dynamics and as I understand for a general chemical reaction
$$\ce{aA + bB -> cC + dD} $$ whose reaction rate, r, can be described by an elementary rate ...
- 61
11
votes
2
answers
2k
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How does an oscillating reaction work?
I watched a Belousov--Zhabotinsky reaction video showing an orange solution that goes to clear and then back to orange (and so forth.)
The reaction goes through a number of cycles before it will no ...
- 6,771
6
votes
1
answer
2k
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Calculating internal energy of methane
I've recently found out my calculated value of internal energy of methane largely deviates from the ab initio output (at $\pu{1000 K}$ $0.058~\text{Hartree} = \pu{152.3 kJ mol-1}$). I used HF method, ...
- 153
2
votes
0
answers
99
views
Why is it impossible to liquefy a gas with only pressure? [duplicate]
Why is it impossible to turn it to liquid by using only pressure after it reaches critical temperature? What happens in the molecular level? If we put enough pressure, the molecules are supposed to ...
- 307
1
vote
1
answer
123
views
Mathematical properties of free Gibbs energy
I'm wandering, if some mathematical properties of the free Gibbs energy (also called thermodynamic potential) are well known.
For instance in chemistry, if $n_i^\alpha$ denotes the number of moles of ...
- 133
3
votes
1
answer
201
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Thermodynamics in Solution (solvation) from quantum chemistry
The gist of the question is "how do I get a heat of formation in solution" - but let me give it some context to be more specific.
I am interested in calculating the thermodynamic values of molecules ...
- 565