# Ethene (C₂H₄) is a hydrocarbon produced during the cracking of long-chain alkanes. Ethene can react with bromine water. Explain why ethene reacts with bromine water but ethane (C₂H₆) does not, and state what is observed when ethene is added to bromine water.

> Eduqas GCSE Chemistry — 2.6 Carbon chemistry / organic chemistry · Explain · 4 marks

> Cracking of long-chain alkanes produces smaller, more useful molecules including alkenes such as ethene. Alkenes are unsaturated hydrocarbons because they contain a carbon-to-carbon double bond.

## Mark scheme (4 marks)

1. Ethene contains a carbon-to-carbon double bond / is unsaturated
2. Ethane is saturated / contains only single bonds / has no double bond
3. The double bond in ethene opens/breaks to allow bromine to add across it (addition reaction)
4. Bromine water is decolourised / changes from orange/brown to colourless (with ethene)

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