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.

![http://www.kshitij-iitjee.com/](useruploads.socratic.org)

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.

![www.spiritsd.ca)

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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