In any population of particles (atoms, ions or molecules)  some will have higher kinetic energies whilst others will have lower kinetic energies. The way that the energies are distributed across a population of particles may be represented by the following histogram.

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This known as a  Maxwell-Boltzmann distribution. It is named after the two scientists who discovered this phenomenon independently of each other and proposed the mathematical function from which the graph derives its shape.

It can be seen from the graph that in any population of reactants there will be particles with various kinetic energies.