Question

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

Answer 1

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.

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.

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.