Gibbs free energy of activation FIX:0000280 Gibbs energy of activation fix.ontology [Wikipedia] The activation energy (Ea) of a reaction is the magnitude of the potential barrier (sometimes called the energy barrier) separating minima of the potential energy surface pertaining to the initial and final thermodynamic state. For a chemical reaction to proceed at a reasonable rate, the temperature of the system should be high enough such that there exists an appreciable number of molecules with translational energy equal to or greater than the activation energy. thermodynamic reaction property