A sealed metal canister contains a fixed amount of gas. The canister is placed in boiling water, causing the temperature of the gas to increase. Explain why the pressure of the gas inside the canister increases.

Eduqas GCSE Physics — 2.2 The kinetic theory and gas pressure · Explain · 4 marks · View as Markdown

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

A sealed metal canister contains a fixed amount of gas at room temperature. The canister is then placed in boiling water.

Model answer (4 marks)

Increasing the temperature raises the kinetic energy of the gas molecules, so they move faster.

Faster molecules collide with the walls more often and with greater force.

Pressure is the perpendicular force per unit area on the walls, so more frequent and harder collisions raise the pressure.

Examiner tips

  • Use the word ‘increase’ for temperature and pressure; mention kinetic energy and collision frequency/force; link to definition of pressure (force/area).
  • Show the causal chain: T↑ → KE↑ → speed↑ → collision frequency↑ & force↑ → P↑.
  • Keep the answer concise – 4 points, one sentence each.

Common mistakes

  • Confusing temperature with pressure; writing that pressure causes temperature rise.
  • Omitting the definition of pressure or the role of collision frequency/force.
  • Using vague terms like ‘more energy’ without linking to kinetic theory.

Mark scheme (4 marks)

  1. Increasing temperature increases the kinetic energy (or speed) of the gas molecules
  2. The faster-moving molecules collide with the walls of the container more frequently
  3. The molecules also collide with the walls with greater force
  4. Pressure is the perpendicular force per unit area on the container walls, so more frequent and harder collisions result in greater pressure

Key terms in this question

pressure · temperature

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