Modified collision theory

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 Modified collision theory:

 Since the collision theory fails in a number of cases giving the rate of reaction values of various gaseous reaction, it is concluded that collisions between molecules cannot be the only factor, required in determining the rate of a reaction. So, Arrhenius modified the simple collision theory. According to this modified theory. 

(I) The collisions between all molecules cause chemical reaction.

(II) The collisions between the molecules which possess energy of activation cause the chemical reaction. It means that if the energy of the colliding molecules is less than the energy of activation, no reaction take place. If the energy is equal to or greater than energy of activation, reaction occurs Thus, eqn (iv), k=ze -Ea/RT  is modified, to account for the deviations from the collision theory, in the form k=pZ e -Ea/RT
   
        Where p is the probability factor which is a measure of an increase or decrease of the speed of reactions. The value of p varies from 1 to 10-⁸ because of a number of weakness, collision theory suffered a serious setback, and a more modern theory, know as Transition state theory has replaced the collision theory.

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