Question
Why do alkenes undergo electrophilic addition reactions?
Solution
Alkenes undergo electrophilic addition reaction. The 
electrons constituting the 
bond in the double bond are more mobile, easily detachable and more easily available for the chemical reaction. This means >C = C< can act as a source of electrons. There are certain reagents (electrophiles) which are capable of adding to alkene molecules forming an addition compound. Since such reactions are initiated by the electrophiles, hence are known as Electrophilic addition reactions.
The mechanism proceeds in two steps:
(i) Electromeric effect and electrophilic attack.
(ii) Attack of nucleophile. The nucleophile released in slow step combines with carbocation to give the addition product. 
