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Kinetic Theory of Gases (CIE A Level Physics)

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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

Examiner Tip

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

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Ashika

Author: Ashika

Expertise: Physics Project Lead

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.