So if the Gibbs free energy is zero, the reaction has achieved equilibrium and is said to be neither spontaneous nor non spontaneous. In such a case, the rate of the four reaction going from reactants to products is equal to the rate of the reverse reaction going from products back to reactants. Now let's move on to Activation energy. So what exactly is the activation energy? Well, any reaction has some activation energy and this is simply the amount of energy that we have to input for the reaction to take place to convert the reactants to the products or in reverse. Now let's suppose we go from reactants to products.