Explain the difference between a physical change and a chemical change. Give two examples of each and justify your choices.
Answer
Physical change: state change without new substance; chemical change: formation of new substance
The correct answer is Physical change: state change without new substance; chemical change: formation of new substance — Justify: in each physical example no new chemical species; in chemical examples new compounds are formed.
Step-by-step solution
- Define physical change – only state of matter changes, composition stays the same.
- Give example 1: melting ice – solid to liquid, water remains H₂O.
- Give example 2: boiling water – liquid to vapour, still H₂O.
- Define chemical change – atoms combine to form new substances with different properties.
- Give example 1: burning paper – forms ash, carbon dioxide – new compounds.
- Give example 2: rusting iron – iron oxidises to iron(III) oxide, new compound.
- Justify: in each physical example no new chemical species; in chemical examples new compounds are formed.
Common mistake: Confusing state change with chemical change
Concept tested: Distinguishing physical and chemical changes
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