Collision Theory

11SCI - Chemical Tūhura

Finn LeSueur



  • To explain how reactions happen due to collisions between particles
  • To explain the term ‘activation energy’
  • To describe the factors that affect the reaction rate.

Reactions, particles and collisions

  • Reactions take place when particles collide with a certain amount of energy
  • The minimum amount of energy needed for the particles to react is called the activation energy, and is different for each reaction

The rate of a reaction depends on two things:

  • the frequency of collisions between particles,
  • the energy with which particles collide.

If particles collide with less energy than the activation energy, they will not react. The particles will just bounce off each other.

Changing the Rate of Reaction

Anything that increases the number of successful collisions between reactant particles will speed up a reaction.

  • increased temperature,
  • increased concentration of dissolved reactants, and increased pressure of gaseous reactants,
  • increased surface area of solid reactants,
  • use of a catalyst.