GIBS free energy basically describes the difference between the energy of the reactants and the products. But activation energy describes how quickly a reaction actually takes place. So Gibbs free energy talks about where that equilibrium will be achieved while Activation energy talks about how quickly that equilibrium will actually be achieved. And so once again, as we'll see in more detail in a future lecture, the apex of this curve describes the energy of the transition state. Now, what exactly does the enzyme do and how does the enzyme affect the activation energy? So we said previously that the enzyme does not change the Gibbs free energy of the reaction.