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How does the particle model explain gas pressure, and how do pressure, volume and temperature relate?

Gas pressure as the result of particle collisions, the link between temperature and particle speed, and how pressure, volume and temperature are related.

A focused answer to WJEC GCSE Physics topic 1.8 on kinetic theory, covering gas pressure as the result of particle collisions, the link between temperature and average particle speed, and how the pressure, volume and temperature of a fixed mass of gas are related.

Generated by Claude Opus 4.89 min answer

Reviewed by: AI editorial process; not yet individually human-reviewed

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  1. What this topic is asking
  2. What causes gas pressure
  3. Temperature and particle speed
  4. Pressure, volume and temperature
  5. Try this

What this topic is asking

WJEC wants you to explain gas pressure using particle collisions, link temperature to particle motion, and describe how pressure, volume and temperature of a gas are related. This is part of topic 1.8 Kinetic theory in Unit 1 of WJEC GCSE Physics (3420).

What causes gas pressure

Temperature and particle speed

Pressure, volume and temperature

These ideas explain many everyday observations. A car tyre feels harder on a hot day because the warmer air inside has faster particles and a higher pressure. A sealed can of gas can burst if it is thrown on a fire, because heating raises the pressure until the can fails. A bicycle pump warms up as you compress the air quickly, and a balloon shrinks if you cool it in a freezer. In each case the same chain of reasoning applies: temperature controls how fast the particles move, and the frequency and force of their collisions with the walls set the pressure. Being able to talk through this chain clearly, from particle speed to collisions to pressure, is exactly what the longer explain questions reward.

Try this

Q1. State what the temperature of a gas tells you about its particles. [1 mark]

  • Cue. Their average kinetic energy (how fast they move on average).

Q2. A gas at 200 kPa200\,\text{kPa} in 30 cm330\,\text{cm}^3 is compressed to 10 cm310\,\text{cm}^3 at constant temperature. Find the new pressure. [2 marks]

  • Cue. P2=200×3010=600 kPaP_2 = \dfrac{200 \times 30}{10} = 600\,\text{kPa}.

Exam-style practice questions

Practice questions written in the style of WJEC exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

WJEC 20193 marksUse the particle model to explain why the pressure of a gas in a sealed container increases when it is heated.
Show worked answer →

A topic 1.8 Explain question. Heating the gas gives the particles more kinetic energy, so they move faster on average (1 mark). The faster particles hit the walls more often and with greater force (1 mark), and since pressure is the force per unit area from these collisions, the pressure increases (1 mark). Markers reward the faster particles, the more frequent and harder collisions, and the resulting rise in pressure. A common error is to say the particles get bigger or that there are more of them.

WJEC 20214 marksA gas is compressed to a smaller volume at constant temperature. Explain what happens to its pressure, and why.
Show worked answer →

A topic 1.8 Explain question. At constant temperature the particles move at the same average speed (1 mark). Squeezing the gas into a smaller volume packs the same number of particles into less space, so they hit the walls more often (1 mark). More frequent collisions per unit area mean a greater pressure, so the pressure increases (1 mark). The pressure and volume are inversely related: halving the volume doubles the pressure at constant temperature (1 mark). Markers reward the constant speed, the more frequent collisions in the smaller volume, the rise in pressure and the inverse relationship.

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