Question

Explain the mechanism of chlorination of methane.

Answer 1

The mechanism involves a chain reaction. During a chain reaction, for every reactive species you start off with, a new one is generated at the end - and this keeps the process going. The over-all process is known as free radical substitution, or as a free radical chain reaction.
1) Chain initiation: The chain is initiated (started) by UV light breaking a chlorine molecule into free radicals
$C{l}_2\to 2C{l}^{.}$
2) Chain propagation reactions: These are the reactions which keeps the chain going.
$C{H}_4+C{l}^{.}\to C{H}_3^{.}+HCl$
$C{H}_3^{.}+C{l}_2\to C{H}_{3}Cl+C{l}^{.}$
3) Chain termination reactions: These are reactions which remove free radicals from the system without replacing them by new ones
$2C{l}^{.}\to C{l}_2$
$C{H}_3^{.}+C{l}^{.}\to C{H}_{3}Cl$
$C{H}_3^{.}+C{H}_3^{.}\to C{H}_{3}C{H}_3$