Collision theory of reaction rates is a theory that assumes that, for reaction to occur, reactant molecules must collide with an energy greater than some minimum value and with the proper orientation. The minimum energy of collision required for two molecules to react is called the activation energy, Ea. The value of Ea depends on the particular reaction.
In collision theory, the rate constant for a reaction is given as a product of three factors:
(1) Z, the collision frequency
(2) f, the fraction of collisions having energy greater than the activation energy,and
(3) p, the fraction of collisions that occur with the reactant molecules properly oriented.
Thus, k ==>Zfp