IB Chemistry home > Syllabus 2016 > Kinetics > Collision theory

Syllabus ref: 6.1

Collision theory explores the interaction between the kinetic theory of molecules and the processes that occur when particles undergo chemical reactions.

Nature of science:

The principle of Occam's razor is used as a guide to developing a theory-although we cannot directly see reactions taking place at the molecular level, we can theorize based on the current atomic models. Collision theory is a good example of this principle.


Essential idea: The greater the probability that molecules will collide with sufficient energy and proper orientation, the higher the rate of reaction.

Species react as a result of collisions of sufficient energy and proper orientation.

Activation energy (Ea) is the minimum energy that colliding molecules need in order to have successful collisions leading to a reaction.

By decreasing Ea, a catalyst increases the rate of a chemical reaction, without itself being permanently chemically changed.

Applications and skills

Description of the kinetic theory in terms of the movement of particles whose average kinetic energy is proportional to temperature in Kelvin.

Explanation of the effects of temperature, pressure/concentration and particle size on rate of reaction.

Construction of Maxwell-Boltzmann energy distribution curves to account for the probability of successful collisions and factors affecting these, including the effect of a catalyst.

In Chapter 6.2