3.5 describe the substitution reaction of methane with bromine to form bromomethane in the presence of UV light.

Methane and bromine react together in the presence of ultra-violet radiation to form bromomethane.

CH4 (g) + Br2 (g) ---> CH3 Br(g) + HBr (g)

Since one atom in methane (a hydrogen atom) has been replaced by another atom (a bromine atom) this reaction is called a substitution reaction.