Use the kinetic theory to explain why the pressure of a fixed mass of gas increases when its temperature is raised, while its volume stays the same.

WJEC GCSE Physics (Wales) — 1.8 Kinetic theory · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Gas particles move faster when the temperature is raised, so their average kinetic energy increases.
The faster particles collide with the walls of the container more frequently.
Each collision exerts a greater force on the wall.
Because the area of the wall is unchanged, the increased force gives a higher pressure.

Examiner tips

Use the word ‘explain’ – describe the chain of events from temperature to pressure.
Show the link between kinetic energy, collision frequency and force.
Mention that volume is constant so area of the wall is unchanged.
Use correct terminology: kinetic energy, collision, force, pressure.

Common mistakes

Failing to mention that temperature is linked to kinetic energy.
Confusing pressure with volume – not recognising that volume is constant.
Using vague phrases like ‘more energy’ without explaining the effect on collisions.

Mark scheme (4 marks)

Gas particles move faster / have greater (average) kinetic energy at higher temperature
Particles collide with the walls of the container more frequently
Particles hit the walls with greater force
Greater force on the same area means greater pressure (since volume is unchanged)

Key terms in this question

kinetic theory · pressure · temperature