Kinetic Theory of Gases (Cambridge International A-Level Physics)

Assumptions of the Kinetic Theory of Gases

Spec point — 15.3.1

• 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

Exam Hint Make sure to memorise all the assumptions for your exams, as it is a common exam question to be asked to recall them.