Let's say there is a rxn : A+B -> C+D
i) Enthalpy of reaction/gibbs free energy of a reaction can be calculated using the thermochemistry output from Gaussian.
deltaG = sum(Gc +Gd) - sum(Ga +Gb).
ii) On the other hand, if we use IRC. We can obtain the reaction mechanism (A+B) --> TS --> (C+D)
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The results I obtained from
i) showed that the reaction is thermodynamically unfavourable. (deltaG > 0)
ii) showed that (C+D) is at a lower energy than (A+B) which means the reaction is thermodynamically favourable.
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I understand that by using i) to determine the reaction feasibility, we assume that A and B are located far enough to have the interaction neglected. Same as C and D. Will this incur some errors here?
As far as I am concerned, the distance of A and B we set in Gaussian has an effect on the output energy.
So in this case, IRC is a better representation of the reaction?
Another question, for example I want to know whether the synthesis of the new chemical is feasible or not. In this case is it appropriate to use the deltaG = sum(Gc +Gd) - sum(Ga +Gb) to get a quick answer to the feasibility of the reaction using Gaussian.
Thank you.
Please look at the following below links which may help you in your analysis:
http://web.thu.edu.tw/ghliu/www/pdf/thermo.pdf
https://www.scribd.com/document/344972415/GIBBS-FREE-ENERGY-OF-FORMATION-GAUSSIAN-pdf
Thanks
The starting point of thermodynamic logic is: 1) opposing perpetual motion. 2) The irreversibility of dynamics. Let's look at how to get Carnot efficiency = 1-T1/T2.
1.1 There are many kinds of type 2 perpetual motors, each of which is a natural phenomenon.
A) Machine A: against the irreversibility of thermodynamics (diffusion, heat conduction, friction, etc) - dynamics;
B) Machine B: Utilizing the Difference of Carnot Efficiency (Reversible Thermodynamics) - Thermodynamics
1.2 A and B belong to different disciplines. There is a parallel relationship between them and there is no logical mutual inevitability.
1.3. Logic of the Second Law of Thermodynamics:
Experience induction, deny that A machine==> B machine can not be manufactured==> All material Kano efficiency: 1-T1/T2.
1.4 The logic of the second law of thermodynamics violates the physical logic that A and B cannot be inferred from each other.
1.5 The second law of thermodynamics elevates the "irreversibility", which is in fact only a kinetic experience.
📷 Detailed discussion can be found in the following figure.
The so-called "entropy " doesn't exist at all.
During the process of deriving the so-called entropy, in fact, ΔQ/T can not be turned into dQ/T. That is, the so-called "entropy " doesn't exist at all.
The so-called entropy was such a concept that was derived by mistake in history.
It is well known that calculus has a definition,
any theory should follow the same principle of calculus; thermodynamics, of course, is no exception, for there's no other calculus at all, this is common sense.
Based on the definition of calculus, we know:
to the definite integral ∫T f(T)dQ, only when Q=F(T), ∫T f(T)dQ=∫T f(T)dF(T) is meaningful.
As long as Q is not a single-valued function of T, namely, Q=F( T, X, …), then,
∫T f(T)dQ=∫T f(T)dF(T, X, …) is meaningless.
1) Now, on the one hand, we all know that Q is not a single-valued function of T, this alone is enough to determine that the definite integral ∫T f(T)dQ=∫T 1/TdQ is meaningless.
2) On the other hand, In fact, Q=f(P, V, T), then
∫T 1/TdQ = ∫T 1/Tdf(T, V, P)= ∫T dF(T, V, P) is certainly meaningless. ( in ∫T , T is subscript ).
We know that dQ/T is used for the definite integral ∫T 1/TdQ, while ∫T 1/TdQ is meaningless, so, ΔQ/T can not be turned into dQ/T at all.
that is, the so-called "entropy " doesn't exist at all.
.
.
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Why did the wrong "entropy" appear ?
In summary , this was due to the following two reasons:
1) Physically, people didn't know Q=f(P, V, T).
2) Mathematically, people didn't know AΔB couldn‘t become AdB directely .
If people knew any one of them, the mistake of entropy would not happen in history.
Please read my paper and those answers of the questions related to my paper in my Projects.
https://www.researchgate.net/publication/230554936_Entropy_A_concept_that_is_not_a_physical_quantity
1. The second law of thermodynamics loses the ability of quantitative prediction.
2. Data processing method of law 2 of thermodynamics violates scientific discipline: modifying experimental data to satisfy theory
See the picture for details.
3. The second law of thermodynamics can only be called science if it reaches the same quantitative prediction ability as Newton's second law, otherwise it is pseudoscience.
Comparison of New and Old Thermodynamics
1. Logic of the Second Law of Thermodynamics: Subjectivism, Logical Jump, Interdisciplinary Argumentation.
2. New thermodynamics pursues universality, two theoretical cornerstones:
2.1 Boltzmann formula: ro=A*exp(-Mgh/RT) - Isotope centrifugal separation experiments show that it is suitable for gases and liquids.
2.2. Hydrostatic equilibrium: applicable to gases and liquids.
3. The second and third sonic virial coefficients of R143a derived from the new thermodynamics are in agreement with the experimental results.
3.1. The third velocity Virial coefficient derived is in agreement with the experimental data, which shows that the theory is still correct when the critical density is reached.
4. See Appendix Pictures and Documents for details.
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