A sealed metal canister contains gas at room temperature. The canister is placed in boiling water and left until the gas inside reaches the same temperature as the water. Explain, using kinetic theory, why the pressure of the gas inside the canister increases.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A sealed metal canister contains gas at room temperature. When placed in boiling water, the pressure gauge on the canister shows a higher reading than before.
Model answer (5 marks)
The gas particles gain kinetic energy as the temperature rises, so they move faster.
Because they move faster, they collide with the walls more often.
Each collision is harder, exerting a greater force on the wall.
The canister is sealed and rigid, so its volume does not change.
With the same area but greater force from the collisions, the pressure inside the canister increases.
Because they move faster, they collide with the walls more often.
Each collision is harder, exerting a greater force on the wall.
The canister is sealed and rigid, so its volume does not change.
With the same area but greater force from the collisions, the pressure inside the canister increases.
Examiner tips
- Use the phrase ‘gain kinetic energy’ to show understanding of temperature rise.
- Mention both increased collision frequency and force per collision.
- State that the volume is constant because the canister is rigid and sealed.
- Link the increased force per unit area directly to the rise in pressure.
Common mistakes
- Failing to explain why the particles move faster (missing kinetic energy link).
- Ignoring that the volume remains constant, leading to a wrong conclusion about expansion.
- Using vague terms like ‘more pressure’ without detailing the kinetic theory mechanism.
Mark scheme (5 marks)
- The gas particles move faster / have greater kinetic energy at higher temperature
- The particles collide with the walls of the canister more frequently
- Each collision exerts a greater force on the walls / collisions are harder / more forceful
- The volume of the canister stays the same / cannot expand because it is sealed and rigid
- More force per unit area on the walls means greater pressure / pressure increases because of increased force on the same area
Key terms in this question
kinetic theory · pressure · temperature
Related
- All WJEC A-Level Physics (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Kinetic theory and gases (A-Level only) questions
- A fixed amount of gas is trapped inside a sealed bicycle pump with the nozzle bl…
- A gas is trapped inside a rigid steel cylinder. The cylinder is placed in a free…
- A driver is travelling along a motorway at a constant velocity when they suddenl…
- A car is travelling at high speed along a motorway when the driver notices a haz…