Question

Give two examples of addition reactions.

Answer 1

1. Addition of hydrogen (hydrogenation): Ethene reacts with hydrogen gas when heated in the presence of a catalyst like nickel to give ethane. The addition of hydrogen across the double bond is called hydrogenation.
   \[\ce{\underset{Ethene}{CH2 = CH2} + H2 ->[Ni][300^\circ C] \underset{Ethane (Saturated)}{CH3 - CH3}}\]
2. Addition of halogens (halogenation): When chlorine gas is passed into an inert solvent like CCl₄ containing dissolved ethene at room temperature, one molecule of Cl₂ adds across the double bond to give 1, 2-dichloroethane.
   \[\begin{array}{cc}
   \ce{\underset{Ethene}{CH2 = CH2} + Cl2 -> CH2 - CH2}\\
   \phantom{...............................}|\phantom{..........}|\\
   \phantom{...............................}\ce{\underset{(Ethylene chloride)}{\underset{1, 2-Dichloroethane}{\ce{Cl}\phantom{........}\ce{Cl}}}}
   \end{array}\]