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Organic Reaction Mechanisms

Posted: Mon Mar 06, 2017 8:17 pm
by Lubna_Abdulmajeed_2A
In the introduction to Organic Chemistry book, on page 161, there is an equation that states the following:
G*=H*-TS* (standard gibbs free energy of activation = standard enthalpy of activation - temperature*standard entropy of activation) and below it, there is a statement that says in this case delta G* is always unfavorable, meaning positive. However, why are we considering the gibbs free energy of activation to be unfavorable? why cant it be favorable for the transition state?

Thanks!

Re: Organic Reaction Mechanisms

Posted: Mon Mar 06, 2017 9:03 pm
by kara_kremer_2N
If you look at a PEDD diagram(graph), the energy in the transition state is always higher than the reactants. This means that from the reactants to the transition state, G standard will always be positive and unfavorable. If this were not the case, the transition state would not be the transition state because the transition state is the peak of the energy barrier.