Important Definitions:

Active Molecules:

  • Those molecules which attain the minimum energy required for a chemical reaction.

Activation Energy:

  • Minimum amount of energy required by a reactant molecule to participate in a reaction is called Activation energy.

Threshold Energy:

  • Minimum amount of energy which must be associated with the molecules so that their collision results into product formation.
  • Threshold energy = Activation energy + Energy Possessed by molecules.


Collision Frequency:

The number of collisions taking place per second per unit volume of the        reaction mixture is known as Collision Frequency Z.
Incase of binary collision Z = 1025   to   1028.

According to collision theory

  • Reacting species must possess the adequate energy to overcome the energy barrier
  • Reacting species must be properly oriented at the time of collision.
  • Reactant → Activated Complex → Product
  • The molecule which have sufficient activation energy from activated complex which decompose in product.
  • Orientation of molecule:-


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