A metal perfume bottle contains liquid perfume and perfume vapour above the liquid. The bottle is sealed. Explain, using kinetic theory, why the pressure inside the bottle increases when the bottle is left in a warm car on a sunny day.

Eduqas A-Level Physics — 3.3 Kinetic theory · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (5 marks)

The temperature rise gives the perfume vapour particles more kinetic energy, so they move faster. Faster particles collide with the bottle walls more often and with greater force. Because the bottle is sealed, its volume cannot change. The increased frequency and force of the collisions per unit area raise the pressure inside the bottle.

Examiner tips

  • Use the phrase "gain kinetic energy" and "move faster" to show temperature effect.
  • Mention both "more frequent" and "greater force" collisions.
  • State that the volume is fixed due to the sealed bottle.
  • Link the increased collisions to higher pressure.

Common mistakes

  • Writing that the volume increases, which is incorrect for a sealed bottle.
  • Using vague terms like "more energy" without specifying kinetic energy or faster motion.
  • Omitting the fixed volume point, which is essential for the reasoning.

Mark scheme (5 marks)

  1. The particles of the perfume vapour gain kinetic energy / move faster when temperature increases
  2. The particles collide with the walls of the bottle more frequently
  3. The particles hit the walls with greater force
  4. The volume of the sealed bottle stays constant / fixed
  5. More frequent and more forceful collisions per unit area on the walls result in greater pressure

Key terms in this question

kinetic theory · pressure

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