# Halogenoalkanes are organic compounds in which one or more hydrogen atoms in an alkane have been replaced by a halogen atom. Chloroethane (C₂H₅Cl) is an example of a halogenoalkane. Explain how chloroethane is formed from ethane, and describe the type of reaction that occurs, giving the name of the process and the conditions required.

> Edexcel A-Level Chemistry (9CH0) — 6.4 Halogenoalkanes · Explain · 5 marks

> Halogenoalkanes can be produced from alkanes by substitution reactions in the presence of ultraviolet light. In these reactions, a hydrogen atom is replaced by a halogen atom. Chloroethane, for example, can be made from ethane and chlorine.

## Mark scheme (5 marks)

1. A hydrogen atom in ethane is replaced by a chlorine atom (substitution reaction named or implied by 'replacement')
2. The reaction is called free-radical substitution (or photochemical substitution)
3. Ultraviolet (UV) light is required as the condition / energy source
4. The Cl–Cl bond in chlorine is broken homolytically (each atom receives one electron), producing chlorine free radicals
5. A chlorine free radical reacts with ethane, removing a hydrogen atom to form HCl and an ethyl free radical, which then reacts with Cl₂ to form chloroethane (chain propagation described)

## Key terms

- [halogenoalkane](https://www.gradenine.co.uk/glossary/halogenoalkane)

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Source: [GradeNine](https://www.gradenine.co.uk/q/halogenoalkanes-are-organic-compounds-in-which-97793e10) · Published by Druglandscape Ltd.