Explain why freezing 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).

Water can be frozen to form ice, which can then be melted back to water.

Model answer (4 marks)

Freezing is a physical change because the substance keeps its chemical identity – the water molecules remain H₂O.

During freezing the arrangement of the molecules changes; they become more ordered and closer together, forming a solid lattice.

No new substances are produced, so the chemical structure does not change.

Because the change is only in physical arrangement, the ice can be melted back to liquid water, restoring the original properties.

Examiner tips

  • Use the word "physical change" and explain that the chemical structure is unchanged; mention the reversible nature of the process.
  • Show the change in particle arrangement (more ordered/closer) and that no new substances are formed.
  • Keep the answer concise – 4 marks can be earned with 4 short points.
  • Use UK spelling (e.g. "organisation").

Common mistakes

  • Confusing the change with a chemical reaction and claiming new substances are formed.
  • Failing to mention that the change is reversible and that the chemical structure remains H₂O.
  • Using vague language such as "the state changes" without linking to particle arrangement or chemical identity.

Mark scheme (4 marks)

  1. The substance retains / can restore its original properties when the change is reversed
  2. The chemical structure of the substance does not change during freezing
  3. Only the physical properties / arrangement of the particles change (e.g. particles become more ordered / closer together)
  4. In a chemical change the substance does not restore its original properties when the change is reversed, but in a physical change it does

Key terms in this question

physical change · chemical change · freezing

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