Collision theory unimolecular reactions

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 Collision theory of unimolecular reactions:

 This theory was proposed independently by max trautz in 1916 and William Lewis in 1918. This theory qualitatively explain how chemical reactions occur and why reaction rates differ for different reaction. According to this theory, the reacting molecules must collide to react as a result of which the chemical reaction occurs. But, in fact, not all collisions are effective. Only a certain percentage of total number of collisions produce any significant chemical reaction. In other words, successful (i.e., effective) collisions give rise to chemical reaction. It is just like that a few number of crackers burst with sound and hence effective while others are ineffective producing no sound. The effective collisions between the reacting molecules causing any chemical change depends on two conditions (e.g., postulates) :
 
(I) the colliding molecules must have enough energy, known as activation energy to cause a reaction, and.

(II) the reacting molecules must hit with each other with proper orientation, i.e., in a correct direction at proper site (position) to lose and then accommodate the constituent particle.

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