Halogens & Alkanes (Edexcel IGCSE Chemistry (Modular))
Revision Note
Written by: Stewart Hird
Reviewed by: Lucy Kirkham
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 a solvents, refrigerants, propellants and pharmaceuticals
Examiner Tips and Tricks
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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