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

(Taken directly, word for word (because I am extremely lazy right now) from Hannah Help Chemistry)

In UV light bromine and methane will form bromomethane:

CH₄  +  Br₂ >CH₃Br  +  HBr

What has happened in this reaction is a bromine has taken the place of a hydrogen (substitution.)