Explain why a fixed mass of gas exerts a greater pressure on the walls of its container when the temperature of the gas is increased at constant volume.
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 particles.
The faster particles collide with the walls more often.
Each collision transfers more momentum (force) because the particles are moving faster.
Pressure, being force per unit area, rises because both the collision frequency and the force per collision increase.
The faster particles collide with the walls more often.
Each collision transfers more momentum (force) because the particles are moving faster.
Pressure, being force per unit area, rises because both the collision frequency and the force per collision increase.
Examiner tips
- Use the kinetic‑energy argument first, then link to collision frequency and force, finally state the pressure definition.
- Show the logical chain: T↑ → KE↑ → speed↑ → collision frequency↑ & force↑ → P↑.
- Keep the answer concise and use the exact terminology: kinetic energy, momentum, force, pressure.
Mark scheme (4 marks)
- Increasing temperature increases the average kinetic energy (or speed) of the gas particles.
- Faster-moving particles collide with the container walls more frequently.
- Each collision transfers greater momentum / force to the wall because particles are moving faster.
- Pressure is the force per unit area exerted on the walls, so both greater frequency and greater force of collisions result in increased pressure.
Key terms in this question
Related
- All IB DP Chemistry Higher Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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