Explain why the pressure of a fixed amount of gas inside a sealed container increases when the temperature of the gas is raised.

Edexcel GCSE Physics (1PH0) — 14.1 Particle model · Explain · 4 marks · View as Markdown

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

A sealed metal container holds a fixed amount of gas. A student notices that when the container is placed in hot water, a pressure gauge attached to the container shows a higher reading.

Model answer (4 marks)

Increasing the temperature raises the kinetic energy of the gas particles, so they move faster. Faster particles collide with the walls more often and each impact delivers a larger force. Because the area of the walls is unchanged, the increased force per unit area gives a higher pressure.

Examiner tips

Use the word ‘explain’ to show cause and effect, not just state facts.
Mention both the increase in collision frequency and the greater impact force.
Show the pressure formula (P=F/A) to link force and area.
Keep the answer concise – 4 marks can be earned with 3–4 short sentences.

Common mistakes

Confusing temperature with pressure or volume.
Failing to mention the increased collision frequency.
Using vague terms like ‘more energy’ without linking to speed or force.

Mark scheme (4 marks)

Increasing temperature increases the kinetic energy (and speed) of the gas particles
Particles collide with the walls of the container more frequently
Each collision transfers greater force / the particles hit the walls with greater impact
Greater force on the same area means pressure increases (since pressure = force ÷ area and area is unchanged)

Key terms in this question

pressure · temperature · gas