Hseb Notes - Chemistry XII - Collision theory of reaction - (Chemical kinetics)

Collision theory of Reaction

A reaction takes place because the reacting molecules collide with each other . All the collisions cannot lead to formation of products. The collisions which lead o the formation of products are called effective collisions. The number of effective collisions is dependent upon following two factors

• Energy of collision

• Proper Orientation of reacting species

The reacting specieshave their own kinetic energy. Evergy reaction has a certain energy barrier which is called threshold energy. The average K.E. of the species mostl is not sufficient to overcome this energy barrier. An additional energy is to be provided to reacting species to overcome this energy barrier called activation energy. A reaction having lower actication energy occurs fast because large number of molecules will soon cross the energy basrrier Similarly the reaction with higher activation energy will be slow . The reaction having activation energy zero is nearly explosive.

                Also, the reacting species should be oriented towards favorable sites of collision to have effective collisions.

Eg.          H₂                 +             O₂                 ------------>         2HI

                H             +             I              

------------>         2HI

                H             +             I

                Proper Orientation

                H             H             +             I               I               ------------>      No Products

                Improper Orientation