CH2=CH2 + H2 →CH3– CH3
Unsaturated hydrocarbons add hydrogen in the presence of catalysts such as palladium or nickel to give saturated hydrocarbons. This reaction is called the addition reaction.
A chemical reaction in which two or more reactants combine to form a larger single product is known as an addition reaction. But only chemical compounds containing multiple bond character can undergo an addition reaction as a double or triple bond is usually broken to form the required single bonds.
Example: Hydro chlorination of propane
CH3CH = CH2 + HCl → CH3C+HCH3 + Cl− → CH3CHClCH3