Kinetic Theory of Gases (Cambridge (CIE) A Level Physics): Revision Note

Assumptions of the kinetic theory of gases

• The kinetic theory of gases is based on the following assumptions:

  • Molecules of a gas behave as identical (or all have the same mass)

  • Molecules of gas are hard, perfectly elastic spheres

  • The molecules are in continuous random motion

  • There are no forces of attraction or repulsion between the molecules

  • External forces (e.g. gravity) are ignored

  • Newton's laws apply

  • The volume of the molecules is negligible compared to the volume of the container

  • The molecules collide perfectly elastically with the walls of the container exerting a pressure upon them

  • The time of a collision is negligible compared to the time between collisions

  • There are a very large number of molecules

Gas molecules in a box

Gas molecules move about randomly at high speeds