Substitution Reactions of Alkanes with Chlorine
Chemistry: Cambridge International GCSE Supplement, topic 11.4.3
Substitution Reactions of Alkanes with Chlorine
Alkanes react with chlorine in a photochemical substitution reaction using UV light to replace hydrogen atoms with chlorine.
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What is a substitution reaction?
- A substitution reaction replaces one atom or group in a molecule with another atom or group.
- Alkanes undergo substitution reactions to form new compounds.
- Substitution in alkanes typically involves replacing a hydrogen atom.
- These reactions help make useful chemicals from simple alkanes.
Alkanes and chlorine reaction overview
- Alkanes react with chlorine in a substitution reaction.
- This reaction needs ultraviolet (UV) light, which acts as activation energy (Ea).
- UV light starts the reaction by breaking Cl2 into chlorine atoms.
- This type of reaction is called a photochemical reaction because light causes it.
Example - methane and chlorine reaction
- Methane (CH4) reacts with chlorine (Cl2) under UV light.
- A hydrogen atom in methane is replaced by a chlorine atom to form chloromethane (CH3Cl).
- The reaction also produces hydrochloric acid (HCl).
- Structural formula: CH4 + Cl2 → CH3Cl + HCl (monosubstitution).
Test yourself on Substitution Reactions of Alkanes with Chlorine
In a substitution reaction, what happens to an atom or group in a molecule?