The collision model or collision theory is based on kinetic-molecular theory. It seeks to explain the effect of concentration and temperature on the reaction rate. According to the model, reactant molecules only react when they collide with correct orientation and enough energy to overcome the activation energy. Increasing the rate of successful collisions increases the reaction rate.

Figure 1. Two requirements must be satisfied for reactants to collide succesfully: 1) The collision energy must be equal or exceed the activation energy. 2) The orientation must allow the formation of new chemical bonds.