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

Nov 20, 2015

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

Endergonic just means that $\Delta {G}_{\text{rxn}} > 0$. So, the Gibbs' free energy of the products is higher than the Gibbs' free energy of the reactants.

Now, since we do have $\Delta G > 0$, since we know that $\Delta S > 0$, $\Delta H$ must be positive. Either $\Delta H$ is large and positive, or the temperature is low enough such that $\Delta H > T \Delta S$.

$\Delta {G}_{\text{rxn" = DeltaH_"rxn" - TDeltaS_"rxn}}$

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 $\Delta {H}_{\text{rxn}}$ instead, and your y-axis would be the potential energy, NOT the Gibbs' free energy.