Question

\text { Describe the different addition reactions of ethene. }

Short answer

Answer: The four main addition reactions of ethene are: 1. Hydrogenation: Ethene reacts with hydrogen gas to form ethane (C2H6). 2. Halogenation: Ethene reacts with halogens like chlorine or bromine to form dihaloalkanes (e.g., C2H4Cl2 or C2H4Br2). 3. Hydrohalogenation: Ethene reacts with hydrogen halides like HCl or HBr to form halogenated alkanes (e.g., C2H5Cl or C2H5Br). 4. Hydration: Ethene reacts with water to form ethanol (C2H5OH).

Step-by-step solution

1. Hydrogenation Reaction (Addition of Hydrogen)

In this reaction, ethene reacts with hydrogen gas (H2) in the presence of a catalyst, such as platinum or nickel, at a high temperature and pressure. The catalyst helps to break the carbon-carbon double bond, and a hydrogen atom is added to each carbon atom in ethene, resulting in the formation of ethane (C2H6). Here's the reaction: C2H4 + H2 → C2H6.

2. Halogenation Reaction (Addition of Halogens)

In this reaction, ethene reacts with a halogen, such as chlorine (Cl2) or bromine (Br2), to form a dihaloalkane, where the halogen atoms are added to the two carbon atoms. This reaction occurs without the presence of a catalyst or specific conditions. Here's the reaction with chlorine: C2H4 + Cl2 → C2H4Cl2 and with bromine: C2H4 + Br2 → C2H4Br2.

3. Hydrohalogenation Reaction (Addition of Hydrogen Halides)

In this reaction, ethene reacts with a hydrogen halide like hydrogen chloride (HCl) or hydrogen bromide (HBr) to form a halogenated alkane with the hydrogen halide added across the double bond. No catalyst is required for this reaction. Here's the reaction with hydrogen chloride: C2H4 + HCl → C2H5Cl and with hydrogen bromide: C2H4 + HBr → C2H5Br.

4. Hydration Reaction (Addition of Water)

In this reaction, ethene reacts with water (H2O) in the presence of an acid catalyst, usually concentrated phosphoric(V) acid (H3PO4), to form ethanol (C2H5OH). The acid catalyst helps to break the carbon-carbon double bond, and the hydrogen atom and hydroxyl group from water are added to the two carbons. The reaction happens at high temperature and pressure. Here's the reaction: C2H4 + H2O → C2H5OH. These are the main addition reactions of ethene. Each of these reactions involves breaking the carbon-carbon double bond and adding new atoms or groups to the original ethene molecule.