# Methane (CH₄) is a hydrocarbon that burns completely in oxygen. The balanced equation for this reaction is: CH₄ + 2O₂ → CO₂ + 2H₂O. Explain what the term 'hydrocarbon' means, state the law that explains why no mass is lost during this reaction, and explain why the equation must have the same number of atoms of each element on both sides.

> Eduqas A-Level Chemistry — 3.2 Hydrocarbons · Explain · 5 marks

> Methane is the main component of natural gas and is used as a fuel in homes and industry.

## Mark scheme (5 marks)

1. A hydrocarbon contains hydrogen and carbon only
2. The law of conservation of mass states that no atoms are lost or made during a chemical reaction
3. Because no atoms are lost or made, the mass of products equals the mass of reactants
4. Atoms are rearranged during a chemical reaction (but not lost or made), so the same atoms must appear on both sides of the equation
5. Therefore the equation must be balanced — the number of atoms of each element is the same on both sides

## Key terms

- [hydrocarbon](https://www.gradenine.co.uk/glossary/hydrocarbon)
- [balanced equation](https://www.gradenine.co.uk/glossary/balanced-equation)

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- [Revision notes for Eduqas A-Level Chemistry](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/methane-ch-is-a-hydrocarbon-that-81a489c9) · Published by Druglandscape Ltd.