Explain why evaporation is described as a physical change rather than a chemical change.

AQA GCSE Physics (8463) — 4.3.1 Changes of state and the particle model · Explain · 4 marks · View as Markdown

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

A puddle of water gradually disappears on a warm day as the water evaporates into the air.

Model answer (4 marks)

Evaporation is a change of state, the water changes from liquid to vapour.
The chemical structure of the water molecules does not change – the H₂O molecules remain H₂O.
The process is reversible; the vapour can condense back into liquid water.
Because chemical changes are normally irreversible and involve new substances, evaporation does not meet that criterion.

Examiner tips

  • Use the term "change of state" and mention liquid to vapour. State that the molecular composition remains H₂O. Highlight reversibility – condensation. Contrast with irreversible chemical changes.

Common mistakes

  • Saying evaporation is a chemical change. Forgetting to mention the reversibility. Using vague phrases like "water changes" without specifying state change.

Mark scheme (4 marks)

  1. Evaporation is a change of state (from liquid to vapour/gas)
  2. The chemical structure / composition of the substance does not change
  3. The change is reversible (the substance can restore its original properties)
  4. Chemical changes are not (usually) reversible / do not restore original properties, so evaporation does not meet this criterion

Key terms in this question

evaporation · physical change · chemical change

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