Explain what happens to the internal energy of a substance when it is heated and changes state from liquid to gas. Include what happens to the temperature of the substance during the change of state.

AQA GCSE Physics (8463) — 4.3.2 Internal energy and energy transfers · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Heating increases the internal energy of the substance.
During the change of state the temperature remains constant.
The energy supplied is used to increase the potential energy of the particles, not their kinetic energy.
The energy required to change from liquid to gas is the latent heat of vaporisation.

Examiner tips

  • Use the term ‘latent heat of vaporisation’ exactly. Show the temperature stays constant during the phase change. Explain that the energy goes into potential energy, not kinetic.
  • Use the word ‘internal energy’ and ‘potential energy’ – these are the key terms.
  • Mention that heating first raises temperature, then during boiling the temperature stops rising.

Mark scheme (4 marks)

  1. Heating increases the internal energy of the substance
  2. During the change of state, the temperature remains constant / does not change
  3. During the change of state, the energy supplied increases the potential energy of the particles (not the kinetic energy)
  4. The energy required to change state from liquid to gas is the (specific) latent heat of vaporisation

Key terms in this question

internal energy · change of state

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