Methane (CH₄) is a hydrocarbon used as a fuel. When methane burns completely in excess oxygen, carbon dioxide and water are produced. Explain why burning methane is a chemical change and not a physical change.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Methane is the main component of natural gas and is widely used in domestic heating and cooking.
Model answer (4 marks)
Burning methane is a chemical change because it involves a chemical reaction.
1. The reaction is:
CH₄ + 2O₂ → CO₂ + 2H₂O
2. The products, CO₂ and H₂O, have a different chemical composition from the reactant, CH₄.
3. A physical change would only change the state of matter, not the chemical composition.
4. The combustion of methane cannot be reversed to recover CH₄, so it is not a physical change.
1. The reaction is:
CH₄ + 2O₂ → CO₂ + 2H₂O
2. The products, CO₂ and H₂O, have a different chemical composition from the reactant, CH₄.
3. A physical change would only change the state of matter, not the chemical composition.
4. The combustion of methane cannot be reversed to recover CH₄, so it is not a physical change.
Examiner tips
- Use the reaction equation to show the change in composition
- Explain that a physical change only alters state, not composition
- Highlight irreversibility of combustion
Common mistakes
- Confusing the change of state with a chemical change
- Claiming the reaction is reversible
- Forgetting to mention the different chemical formulas of products
Mark scheme (4 marks)
- A chemical change requires a chemical reaction to occur
- The products (carbon dioxide and water) have a different chemical composition to the reactant (methane)
- A physical change only involves a change of state / only changes the form of the chemical
- Burning methane is not a physical change because the chemical composition of the products is different from that of methane / the change cannot simply be reversed to recover methane
Key terms in this question
chemical change · physical change
Related
- All Eduqas GCSE Chemistry revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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