Collision: Two objects coming towards each other with some momentum and then coming in contact with each other is known as a Collision.
According to the collision theory, the molecules must collide with enough energy, known as the activation energy, to prevent the chemical bonds from breaking, in order for a chemical reaction to occur.
Additionally, the molecules must collide in the proper orientation.
If these two requirements are satisfied, a collision is referred to be a successful collision or an effective collision. The frequency of the effective collisions is equal to the rate of a chemical reaction.