Explain why the pressure of a fixed mass of gas increases when its temperature is increased, if the volume of the gas is kept constant.

AQA A-Level Physics (7408) — 3.6.2 Thermal Physics · Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

1. Gas particles are in constant random motion.
2. Pressure is caused by particles colliding with the walls of the container.
3. Increasing temperature increases the average kinetic energy of the particles, so they move faster.
4. Faster particles collide with the walls more frequently.
5. Each collision exerts a greater force on the walls, so the pressure increases.

Examiner tips

Use the exact wording from the mark scheme – e.g. "average kinetic energy" and "collisions are harder". Show the logical chain: motion → collisions → force → pressure. Keep the answer concise and avoid unnecessary detail.

Common mistakes

Confusing temperature with pressure or volume. Failing to mention that collisions become harder (greater force) rather than just more frequent. Using vague terms like "more energy" without linking to kinetic energy.

Mark scheme (5 marks)

Gas particles are in constant random motion
Pressure is caused by particles colliding with the walls of the container
Increasing temperature increases the average kinetic energy of the particles / particles move faster
Faster particles collide with the walls more frequently
Each collision exerts a greater force on the walls / collisions are harder, so pressure increases

Key terms in this question

pressure · temperature