Propane (C₃H₈) is a hydrocarbon fuel used in camping gas stoves. When propane burns completely in oxygen, carbon dioxide and water are produced. Explain why burning propane is a chemical change and not a physical change.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
A chemical change involves a chemical reaction.
The combustion of propane is a reaction:
C₃H₈ + 5O₂ → 3CO₂ + 4H₂O.
The products, CO₂ and H₂O, have a different chemical composition to the reactants, propane and oxygen.
A physical change only changes state; the chemical composition remains the same.
Here propane is converted into different compounds, so it is a chemical change.
The combustion of propane is a reaction:
C₃H₈ + 5O₂ → 3CO₂ + 4H₂O.
The products, CO₂ and H₂O, have a different chemical composition to the reactants, propane and oxygen.
A physical change only changes state; the chemical composition remains the same.
Here propane is converted into different compounds, so it is a chemical change.
Examiner tips
- Use the word "chemical change" and mention a reaction. Show the balanced equation to prove new compounds are formed. Highlight that composition changes, not just state changes.
Common mistakes
- Saying the change is only a state change. Forgetting to mention the new compounds. Using vague terms like "burning" without showing the reaction.
Mark scheme (4 marks)
- A chemical reaction takes place / a chemical change involves a chemical reaction
- The products (carbon dioxide and water) have a different chemical composition to the reactants (propane and oxygen)
- A physical change only involves a change in state / the chemical composition stays the same in a physical change
- Burning propane produces substances that are chemically different / the propane is not simply changing state — it is converted into different compounds
Key terms in this question
chemical change · physical change · hydrocarbon
Related
- All WJEC GCSE Chemistry (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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