Explain why sublimation 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).

Dry ice (solid carbon dioxide) sublimates at room temperature, changing directly from a solid to a vapour.

Model answer (4 marks)

Sublimation is a change of state – the solid CO₂ goes directly to gas without becoming liquid.

Changes of state are physical changes because the substance keeps its chemical identity and its properties; the process is reversible.

In a chemical change the chemical structure changes and a new substance is formed.

During sublimation only the arrangement of the CO₂ particles changes; the chemical structure remains CO₂.

Examiner tips

  • Use the phrase ‘change of state’ to show you know the definition.
  • Explain that the substance’s identity is unchanged – it is still CO₂.
  • Mention reversibility to link to physical change.
  • Avoid saying ‘it turns into gas’ without noting the identity stays the same.”]

Mark scheme (4 marks)

  1. Sublimation is a change of state (from solid directly to vapour/gas, without passing through the liquid phase)
  2. Changes of state are physical changes because the substance retains its original properties / the change is reversible
  3. In a chemical change the chemical structure of the substance changes / a new substance is formed
  4. During sublimation only the arrangement / spacing of the particles changes, not the chemical structure / the substance remains carbon dioxide throughout

Key terms in this question

sublimation · physical change · chemical change

Related

More Changes of state and the particle model questions

▶ Try answering this question with AI marking (free) →