Who this is for: Cambridge IGCSE Coordinated Science (0654) students who want pressure changes — how gas pressure relates to volume, temperature and particle collisions — to become a reliable source of marks in explain questions.
What query it owns: how to understand and revise pressure changes in Cambridge IGCSE Coordinated Science.
Why this is safe: this page owns the pressure changes revision-guide angle, while Tutopiya’s Pressure Changes subtopic page owns the learning resource and the free Pressure Changes quiz owns the practice.

Pressure is the force per unit area exerted by gas particles colliding with container walls. Cambridge IGCSE Coordinated Science (0654) expects you to explain how changing volume or temperature affects gas pressure using the kinetic molecular model. At constant temperature, decreasing volume increases pressure because particles collide more frequently with the walls. This guide links particle behaviour to the explain and describe questions examiners set.

Key takeaways

• Pressure = force per unit area; unit: pascal (Pa) or N/m².
• Gas pressure is caused by particle collisions with container walls.
• Boyle’s law (qualitative): at constant temperature, pressure ↑ as volume ↓.
• Heating a gas at fixed volume increases pressure (particles move faster).
• Always explain pressure changes using the kinetic molecular model.

What are pressure changes in Cambridge IGCSE Coordinated Science?

Gas pressure arises when particles in random motion collide with the walls of their container. Each collision exerts a tiny force; billions of collisions per second produce measurable pressure. When volume decreases at constant temperature, particles hit the walls more often, so pressure increases. When temperature increases at constant volume, particles move faster and collide harder, so pressure increases. Examiners reward explanations rooted in particle behaviour.

Study the diagrams and notes on Tutopiya’s Pressure Changes subtopic page before attempting past-paper questions.

Factors affecting gas pressure

Change (at constant temperature)	Effect on particles	Effect on pressure
Volume decreased	Same speed, more frequent wall collisions	Pressure increases
Volume increased	Same speed, less frequent wall collisions	Pressure decreases
Temperature increased (fixed volume)	Particles move faster, harder collisions	Pressure increases
Temperature decreased (fixed volume)	Particles move slower, softer collisions	Pressure decreases
More particles added (fixed V and T)	More collisions with walls	Pressure increases

How to explain a pressure change — step by step

1. State what variable is changed (volume, temperature, or number of particles).
2. Describe the effect on particle motion or collision frequency.
3. Link to pressure: more frequent or harder collisions → higher pressure.
4. Use the kinetic molecular model vocabulary (particles, collisions, walls).
5. Check your reasoning with the free Pressure Changes quiz.

Pressure changes in past-paper wording: command words that matter

Command word / phrase	What the question wants	Typical pressure stem
Explain	Particle-level reason	”Explain why the pressure increases when the volume is reduced.”
Describe	What happens to pressure	”Describe what happens to the pressure of a fixed mass of gas when it is heated.”
State	Define or name	”State what causes gas pressure.”
Predict	Apply the model	”Predict what happens to pressure if the gas volume is halved at constant temperature.”

Worked exam-style stems (how to answer the wording)

1. “Explain, using the kinetic model, why decreasing the volume of a gas increases its pressure at constant temperature.” Particles have the same average speed, but the container walls are closer together, so particles collide with the walls more frequently, increasing the total force on the walls and therefore the pressure. Reward: same speed + more frequent collisions + higher pressure.
2. “A fixed mass of gas is heated in a sealed container. Explain what happens to the pressure.” Particles gain kinetic energy and move faster; they collide with the walls more frequently and with greater force, so pressure increases. Reward: faster particles + harder/more frequent collisions.
3. “State what is meant by pressure.” Pressure is the force acting per unit area, measured in pascals (Pa) or N/m². Reward: force per unit area + unit.

Test yourself with the Pressure Changes quiz once you can explain volume and temperature effects on gas pressure.

How pressure changes connect to the rest of Coordinated Science

Pressure changes build on the Simple Kinetic Molecular Model Of Matter and link to Measurement Of Temperature (temperature scales). The Cambridge IGCSE Coordinated Science resource hub links every Thermal Physics subtopic.

Common mistakes students make

• Explaining pressure changes without mentioning particle collisions.
• Saying particles slow down when volume is reduced at constant temperature (speed stays the same).
• Confusing pressure (force per area) with force alone.
• Forgetting that pressure explanations must use the kinetic model, not just “it gets squashed”.
• Applying Boyle’s law when temperature is not constant.

When you need more support

If pressure change questions keep costing marks, work through the Pressure Changes quiz, then get focused help from a Cambridge IGCSE Coordinated Science tutor.

Frequently asked questions

What causes gas pressure? Gas particles colliding with the walls of their container; each collision exerts a force, and pressure is force per unit area.

What happens to gas pressure when volume decreases at constant temperature? Pressure increases because particles collide with the walls more frequently.

What is Boyle’s law? At constant temperature, the pressure of a fixed mass of gas is inversely proportional to its volume.

How do I revise pressure changes effectively? Practise kinetic-model explanations for volume and temperature changes, then take the Pressure Changes quiz.

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