3.2.2 Kinetics - Collision theory

Specification

Students should:
  • understand that reactions can only occur when collisions take place between particles having sufficient energy
  • be able to define the term activation energy and understand its significance
  • understand that most collisions do not lead to reaction

Collision theory

Collision theory -- reactions take place as a result of particles (atoms or molecules) colliding and then undergoing a reaction. Not all collisions cause reaction, however, even in a system where the reaction is spontaneous.

The particles must have sufficient kinetic energy, and the correct orientation with respect to each other for them to react. This energy is needed to cause bonds to break, which is essential if reaction is to take place.


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Activation energy

This is the minimum energy that particles colliding must have in order to produce successful reaction. It is given the symbol Ea (Energy of Activation). The energy of particles is a function of their speed (kinetic energy = 1/2mv2).

The activation energy is sometimes called the energy barrier to reaction.


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