James Clerk Maxwell and Ludwig Boltzmann initially developed the kinetic theory of gas. James Clerk Maxwell calculated statistically the distribution of energy amongst molecules in 1859 and in 1871 the Austrian Physicist Ludwig Eduard Boltzmann more generally applied it. The result was the Maxwell-Boltzmann distribution of molecular energies. This explains why at a particular temperature, only a certain number of collisions are effective ones.

Molecules have energy due to their kinetic energy some molecules have high energies and move fast while other molecules have low energies because thy are moving very slowly. However at a higher temperature, a greater proportion posses energies greater to or equal to the activation energy, giving more successful collisions.

From the graphs we can see that the proportion of molecules has energies equal to or greater than the activation energy. At a higher temperature a greater proportion of molecules has at least the activation energy.