Halogens & Alkanes (Edexcel IGCSE Chemistry)
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Spec point — describe the reactions of alkanes with halogens in the presence of ultraviolet radiation, limited to mono-substitution knowledge of reaction mechanisms is not required
Halogens & alkanes
- In a substitution reaction, one atom is swapped with another atom
- Alkanes undergo a substitution reaction with halogens in the presence of ultraviolet radiation
The reaction between methane and bromine in the presence of ultraviolet radiation
In the presence of ultraviolet (UV) radiation, methane reacts with bromine in a substitution reaction
- The equation for the reaction is
methane + bromine → bromomethane + hydrogen bromide
CH4+ Br2→ CH3Br + HBr
- Chlorine will also react with alkanes under the same conditions to form chloromethane
methane + chlorine → chloromethane + hydrogen chloride
CH4+ Cl2→ CH3Cl + HCl
- The products belong to a family called halogenoalkanes or haloalkanes
- Halogenoalkanes have many uses as solvents, refrigerants, propellants and pharmaceuticals
Exam Hint CFC stands for chlorofluorocarbon, an important class of halogenoalkanes, previously used in fridges and air conditioners, but gradually being phased out because of the damage they cause to the ozone layer.
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