Explain the difference between a physical change and a chemical change. Include one example of each type of change in your answer.

Cambridge International IGCSE Chemistry (0620) — 6.1 Physical and chemical changes · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

A physical change is one in which the substance keeps its chemical identity; no new substance is formed and the change is usually reversible. For example, melting ice into water.
A chemical change produces one or more new substances and is normally irreversible. For example, burning magnesium to give magnesium oxide.

Examiner tips

Use the phrase ‘no new substance is formed’ for physical changes and ‘new substance is formed’ for chemical changes.
Give one clear example of each type of change.
Keep the answer concise and use the exact terminology from the mark scheme.
Use the word ‘usually’ to show you understand the typical reversibility of physical changes.

Common mistakes

Saying a physical change is irreversible, or a chemical change is reversible.
Giving an example that actually involves a chemical change for the physical change part, e.g. dissolving salt in water as a chemical change.
Using vague terms like ‘change’ without specifying whether a new substance is formed.

Mark scheme (4 marks)

In a physical change, no new substance is formed (the change is reversible / the substance keeps its chemical identity)
In a chemical change, a new substance is formed (and the change is usually irreversible)
A correct, clearly stated example of a physical change (e.g. melting of ice, boiling of water, dissolving of salt in water, cutting of metal)
A correct, clearly stated example of a chemical change (e.g. burning of magnesium, rusting of iron, thermal decomposition of copper carbonate, reaction of acid with metal)

Key terms in this question

physical change · chemical change