How can I draw an endergonic reaction in a potential energy diagram?

1 Answer
Truong-Son N.
Nov 20, 2015

Exergonic and endergonic qualifications only apply for Gibbs' free energy. Enthalpy applies to potential energy diagrams.

Endergonic just means that DeltaG_"rxn" > 0. So, the Gibbs' free energy of the products is higher than the Gibbs' free energy of the reactants.

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Now, since we do have DeltaG > 0, since we know that DeltaS > 0, DeltaH must be positive. Either DeltaH is large and positive, or the temperature is low enough such that Delta H > TDeltaS.

DeltaG_"rxn" = DeltaH_"rxn" - TDeltaS_"rxn"

So, the reaction is necessarily endothermic, and the reaction coordinate diagram and potential energy diagram look similar.

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The main difference is again, you'd be using DeltaH_"rxn" instead, and your y-axis would be the potential energy, NOT the Gibbs' free energy.

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