Relationship between activation energy and pseudo delta g


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Marie_Bae_3M
Posts: 25
Joined: Wed Sep 21, 2016 2:57 pm

Relationship between activation energy and pseudo delta g

Postby Marie_Bae_3M » Thu Mar 09, 2017 11:55 pm

I used to think that pseudo delta g (as the gibbs free energy of activation) was related to the activation energy (Ea), but it was pointed out that in a reaction profile, pseudo delta g would depend on the difference between reactants' deltaG and transition state's deltaG and Ea would would depend on the difference between the local minimum deltaG and the local maximum (transition state) deltaG. So, is there no correlation at all between gibbs free energy of activation and activation energy? Also on the coursereader, page 86, it says at the bottom that "Ea=pseudo deltaH + RT" and I was not sure how this could be derived? Thank you!

Aishwarya_Natarajan_2F
Posts: 11
Joined: Mon Jul 11, 2016 3:00 am

Re: Relationship between activation energy and pseudo delta g

Postby Aishwarya_Natarajan_2F » Sat Mar 11, 2017 5:03 pm

I don't believe that a correlation doesn't exist, because it is correlated to an extent.

In the case of the reaction, ΔG*= ΔH*−TΔS*, and we know that in the case of a reaction, the ΔG* values are always positive, and part of this is because ΔH* is positive while ΔS* is a negligible value. Because of this ΔG* is highly driven by ΔH*.

Activation energy is Ea = ΔH* +RT. This equation captures the biggest component which is the ΔH* value, and so because of this both ΔG* and Ea have a strong dependence on the ΔH* value and can be related in this sense. However, because of the other terms in these expressions it is not an exact relation.

Samuel_Vydro_1I
Posts: 21
Joined: Fri Jul 22, 2016 3:00 am

Re: Relationship between activation energy and pseudo delta g

Postby Samuel_Vydro_1I » Sun Mar 12, 2017 6:32 pm

Your confusion may strain from the fact that the deltaG is taken from reactant to maxima of a TS while Ea is first from reactant to TS1 in a two step and then from the intermediates to TS2. deltaG disregards the intermediates as a starting point of measurement


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