Lesson focus: Gas pressureThe force acting on each unit of area (pressure = force ÷ area), measured in N/m² (pascals, Pa) or N/cm². arises from particle collisionWhen particles bump into each other or into a surface. with surfaces.
Use the particle model to predict effects of temperature, volume and particle number.
Build on earlier learning
DiffusionYear 7 introduced gas pressure from collisions; this lesson changes the conditions.
Practical
Pressure in gases
- Push in the plunger of a sealed syringe and feel the force needed increase.
- Use the model on this page to change the volume and temperature.
- Explain each change with particle collisions.
Record: How pressure changes with volume and temperature.
Gas pressure in a sealed syringe
Push the plunger in or warm the gas. The same particles hit the walls more often, so the pressure rises.
Controls
You will be successful when you can…
- Explain pressure using collisions.
- Predict heating at fixed volume.
- Predict compression.
- Distinguish sealed and open systems.
Words that carry the science
- pressure
- Normal force per unit area.
- collision
- An interaction that changes particle momentum.
- kinetic energy
- Energy associated with motion.
- compression
- Reducing gas volume.
- atmospheric pressure
- Pressure produced by the atmosphere.
Collisions produce pressure
01Collisions produce pressure
Gas particles move randomly and collide with walls. Their momentum changes, exerting force; combined force per unit area is pressureThe force acting on each unit of area (pressure = force ÷ area), measured in N/m² (pascals, Pa) or N/cm²..
pressureThe force acting on each unit of area (pressure = force ÷ area), measured in N/m² (pascals, Pa) or N/cm². describes collective particle–surface interaction, not something stored inside one particle.
02Temperature and volume alter collisions
Heating raises mean kinetic energyThe energy an object has because it is moving.. In a rigid sealed container, particles hit walls more often and with larger momentum change, raising pressure.
Compressing a fixed amount at constant temperature shortens travel between wall collisions and raises pressure.
03Constraints matter
A flexible balloon can expand when heated; an open container lets particles escape. Fixed-volume predictions do not transfer directly.
atmospheric pressureThe push of the air around us on everything it touches. generally decreases with altitude because less atmosphere lies above.
Compress a sealed syringe
A plunger halves trapped-gas volume slowly.
- Particle number remains fixed.
- Volume decreases.
- Wall collisions become more frequent.
- Force per unit area increases.
How to make the reasoning visible: Pressure rises, assuming temperature stays approximately constant.
Gas-pressure
Illustrative states isolate one variable.
| State | Particles | Volume | Temperature / K | Relative pressure |
|---|---|---|---|---|
| A | 100 | 1.0 | 300 | 1.0 |
| B | 100 | 0.5 | 300 | 2.0 |
| C | 100 | 1.0 | 600 | 2.0 |
| D | 200 | 1.0 | 300 | 2.0 |
Explain A→B and A→C.
Why state control variables?
Check your understanding
Answer from memory, then check against the suggested answer.
What event produces gas pressure?
What happens when a rigid sealed gas is heated?
Why can gases compress?
Why must sealed aerosol cans not be heated?
Why can a balloon expand instead of showing the full rigid-container pressure rise?
Exam Question Practice
Exam Question Practice
Mark points shown after marking
A fixed amount of gas is heated in a rigid sealed container.
Describe what happens to the gas particles when the gas is heated.
(2)Explain why the pressure increases.
(3)Total for this question: 5 marks
Command word: Build an unbroken particle-level causal chain.