The minimum extra amount of energy absorbed by the reactant molecules so that their energy becomes equal to threshold value is called activation energy . In other words, activation energy is the difference between the threshold energy and the average kinetic energy of the reactant molecules, i.e.,
Activation energy = Threshold energy - Average kinetic energy of the reactants
Evidently, lesser is the activation energy, faster is the reaction or greater is the activation energy, slower is the reaction
The physical meaning of the activation energy is that it is the minimum relative kinetic energy which the reactant molecules must possess for changing into the products molecules during their collision. This means that the fraction of successful collision is equal to e-Ea/RT called Boltzmann factor.
