The reaction of HBr with ethene is an example of reaction

Options

A. Polymerisation
B. Substitution
C. addition
D. Condensation

Answer

To determine the type of reaction that occurs when HBr reacts with ethene, we can analyze the process step by step.

### Step-by-Step Solution:

1. **Identify the Reactants**:
- The reactants in this case are ethene (C2H4) and hydrogen bromide (HBr).

2. **Understand the Structure of Ethene**:
- Ethene is an alkene with a double bond between the two carbon atoms: H2C=CH2.

3. **Recognize the Nature of HBr**:
- HBr is a polar molecule, where hydrogen (H) carries a partial positive charge (δ+) and bromine (Br) carries a partial negative charge (δ-).

4. **Mechanism of Reaction**:
- The double bond in ethene is nucleophilic and can attack the δ+ hydrogen of HBr. This leads to the formation of a carbocation intermediate.
- The double bond breaks, and one hydrogen atom attaches to one of the carbon atoms, creating a carbocation on the other carbon.

5. **Formation of Product**:
- The bromide ion (Br-) then attacks the carbocation, resulting in the formation of bromoethane (C2H5Br).

6. **Classify the Reaction**:
- Now, we need to classify the type of reaction:
- **Polymerization**: This involves the joining of multiple monomers to form a polymer. In this case, only one molecule of ethene reacts with one molecule of HBr, so it is not polymerization.
- **Substitution**: This involves replacing one atom or group with another. Here, we are not replacing any atom; instead, we are adding to the double bond.
- **Addition**: This involves adding atoms or groups across a double bond. In this reaction, H and Br are added to the ethene, which fits the definition of an addition reaction.
- **Condensation**: This involves the release of a small molecule (like water) when two reactants combine. No small molecule is released in this reaction.

7. **Conclusion**:
- Based on the analysis, the reaction of HBr with ethene is classified as an **addition reaction**.

### Final Answer:
The reaction of HBr with ethene is an example of an **addition reaction**.

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