Explain, in terms of particles, what happens to the pressure of a fixed quantity of gas inside a sealed container when the temperature of the gas is increased at constant volume.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
Increasing the temperature raises the average kinetic energy of the gas particles.
The faster particles collide with the walls more often.
Each collision exerts a larger force because the particles hit harder (greater momentum transfer).
With the volume fixed, the same wall area receives more or harder collisions.
Thus the pressure of the gas rises – pressure is directly proportional to absolute temperature at constant volume.
The faster particles collide with the walls more often.
Each collision exerts a larger force because the particles hit harder (greater momentum transfer).
With the volume fixed, the same wall area receives more or harder collisions.
Thus the pressure of the gas rises – pressure is directly proportional to absolute temperature at constant volume.
Examiner tips
- Use the word "average kinetic energy" and link temperature to particle speed. Show the chain: temperature → kinetic energy → collision frequency & force → pressure. Mention the constant volume condition explicitly.
- Use the correct UK spelling (e.g. "exert" not "exerts").
Common mistakes
- Failing to state that the volume is constant. Using vague terms like "more particles" instead of "faster particles". Omitting the link between kinetic energy and collision force.
Mark scheme (5 marks)
- Increasing temperature increases the average kinetic energy (or speed) of the gas particles
- Faster-moving particles collide with the container walls more frequently
- Each collision exerts a greater force on the walls (because particles hit harder / with greater momentum)
- The volume is constant, so the same area of wall receives more / harder collisions
- Therefore the pressure of the gas increases (pressure is directly proportional to absolute temperature at constant volume)
Key terms in this question
pressure · temperature · particles · volume
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