A fixed quantity of gas is trapped inside a rigid container at a constant volume. Explain why the pressure of the gas increases when its temperature is raised.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Increasing the temperature raises the average kinetic energy of the gas molecules, so they move faster. Faster molecules collide with the walls more often and each impact has a larger momentum change, exerting a greater force on the walls. The increased force per unit area on the rigid container walls results in a higher pressure.
Examiner tips
- Use the chain: temperature → kinetic energy → speed → collision frequency & force → pressure
- Show the link between force per area and pressure
Common mistakes
- Confusing temperature with pressure directly
- Ignoring the role of collision frequency or force in the pressure increase
Mark scheme (4 marks)
- Increasing temperature increases the average kinetic energy (or speed/velocity) of the gas molecules
- Faster-moving molecules collide with the walls of the container more frequently
- Each collision exerts a greater force on the walls because the molecules are moving faster
- Greater force per unit area on the container walls means greater pressure
Key terms in this question
Related
- All WJEC GCSE Physics (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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