enzymes and gibbs free energy

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mcgill2012

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can someone clarify why enzymes do not lower gibbs free energy?

when faced with this question, i answered that they do.
the following is my reasoning.
enzymes lower Ea of a reaction. since the delta H of a reaction depends on the Ea of the reaction, the lower the Ea, the lower the delta H. gibbs free energy = Delta H - T*delta S.
so shouldnt gibbs free energy decrease proportionally with delta H?

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Ea is dependent on the ability of the molecules to enter the transition/intermediate state. the final energy of the final molecule is the same as it would be without the catalyst. thus, delta G is not altered.
 
can someone clarify why enzymes do not lower gibbs free energy?

when faced with this question, i answered that they do.
the following is my reasoning.
enzymes lower Ea of a reaction. since the delta H of a reaction depends on the Ea of the reaction, the lower the Ea, the lower the delta H. gibbs free energy = Delta H - T*delta S.
so shouldnt gibbs free energy decrease proportionally with delta H?

Gibbs free energy is a function of enthalpy, entropy and temperature, all of which are state functions. The GFE is therefore also a state function, and its value for a given transition is the same, irrespective of the path.
 
Hi,
Sorry to hi-jack your thread. But while we are on the subject of enzymes, would they have any affect of stabilizing the transition state since they do lower the energy of activiation for a rxn?
 
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Hi,
Sorry to hi-jack your thread. But while we are on the subject of enzymes, would they have any affect of stabilizing the transition state since they do lower the energy of activiation for a rxn?

enzymes undergo their affects by stabilizing the transition state (making it lower in energy). the lower the energy of the TS the more capable more reactants are at undergoing the reaction (aka there's less of a barrier) and thus the reaction will proceed faster because of the lower barrier
 
enzymes undergo their affects by stabilizing the transition state (making it lower in energy). the lower the energy of the TS the more capable more reactants are at undergoing the reaction (aka there's less of a barrier) and thus the reaction will proceed faster because of the lower barrier

So in essence, they do affect the dG/thermodynamics of the reaction by decreasing the energy of the TS, right?
 
So in essence, they do affect the dG/thermodynamics of the reaction by decreasing the energy of the TS, right?

Catalysts do not change the overall thermodynamics of a reaction. They change the kinetics of the reaction.

Changing the energy of the TS changes kinetics.

Changing the energy (stability) of the product or reactant changes thermodynamics.
 
Catalysts do not change the overall thermodynamics of a reaction. They change the kinetics of the reaction.

Changing the energy of the TS changes kinetics.

Changing the energy (stability) of the product or reactant changes thermodynamics.

Oh I see now. Thanks for the clarification.
 
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