Collision Theory

In order for some particles to interact, they must collide; thus, by increasing the number of collisions, we can increase the rate of the reaction:

This explains the dependence of a reaction rate on concentration; if there are fewer particles, there are fewer collisions and thus fewer reactions. This also explains the relationship between temperature and reaction rate; the higher the temperature, the more the particles are moving, and the higher the chance they’ll collide with enough energy to react.