Homolytic bond fission takes place in free radical chlorination of methane.
\[
\mathrm{CH}_{3}-\mathrm{H}+\mathrm{Cl}_{2} \stackrel{520-670 \mathrm{~K}}{\text { or hv }}>\mathrm{CH}_{3}-\mathrm{Cl}+\mathrm{HCl}
\]
The reaction occurs by a free radical mechanism which involves the following \( 3 \) steps:
Step 1: Chain initiation

Step 2: Chain propagation
\[
\begin{array}{l}
\mathrm{CH}_{4}+\underset{\text { Methane }}{\mathrm{Cl}}+\underset{\text { Chlorine free radical }}{\mathrm{Cl}} \mathbf{~} \mathbf{~ H}_{3}+\mathrm{H} \mathrm{Cl} \\
\mathrm{CH}_{3}+\mathrm{Cl}-\mathrm{Cl} \stackrel{\mathrm{hv}}{\rightarrow} \mathrm{CH}_{3}-\mathrm{Cl}+\mathrm{Cl} \\
\mathrm{CH}_{3} \mathrm{Cl}+\mathrm{Cl} \rightarrow \mathrm{CH}_{2} \mathrm{Cl}+\mathrm{HCl} \\
\mathrm{CH}_{2} \mathrm{Cl}+\mathrm{Cl}-\mathrm{Cl} \rightarrow \mathrm{CH}_{2} \mathrm{Cl}_{2}+\mathrm{Cl}
\end{array}
\]
Step 3: Chain termination
\[
\begin{array}{l}
\mathrm{Cl}+\mathrm{Cl} \rightarrow \mathrm{Cl}-\mathrm{Cl} \\
\mathrm{CH}_{3}+\mathrm{CH}_{3} \rightarrow \mathrm{CH}_{3}-\mathrm{CH}_{3} \\
\text { (Ethane) } \\
\mathrm{CH}_{3}+\mathrm{Cl} \rightarrow \mathrm{CH}_{3}-\mathrm{Cl}
\end{array}
\]