Chemistry Class 11 NCERT Solutions: Chapter 13 Hydrocarbons Part 1

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Q: 1. How do your account for the formation of ethane during chlorination of methane?

Answer:

Chlorination of methane proceeds via a free radical chain mechanism. The whole reaction takes place in the given three steps.

Step 1: Initiation:

The reaction begins with the homolytic cleavage of Cl – Cl bond as:

Equation

Chlorine free radicals

Step 2: Propagation

In the second step, chlorine free radicals attack methane molecules and break down the Equation bond to generate methyl radicals as:

Equation

Methane

These methyl radicals react with other chlorine free radicals to form methyl chloride along with the liberation of a chlorine free radical.

Equation

Methyl chloride

Hence, methyl free radicals and chlorine free radicals set up a chain reaction. While Equation and Equation are the major products formed, other higher halogenated compounds are also formed as:

Equation

Equation

Step 3: Termination:

Formation of ethane is a result of the termination of chain reactions taking place as a result of the consumption of reactants as:

Equation

Equation

Hence, by this process, ethane is obtained as a by - product of chlorination of methane.

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