Q.Write the equations for the chain reaction between Methane and Chlorine in the presence of light.

Methane reacts with chlorine in sunlight/UV light via a free-radical chain mechanism consisting of initiation (formation of Cl radicals by homolysis), propagation (two repeating steps that regenerate the chain-carrying radical), and termination (radicals combining to end the chain).

The reaction of methane with chlorine in the presence of light (a free-radical substitution / halogenation reaction) proceeds through the following steps:

1. Initiation — light supplies energy to homolytically cleave the weak Cl-Cl bond, generating two highly reactive chlorine free radicals:

   Cl2 --(hv)--> Cl• + Cl•

2. Propagation — a chlorine radical abstracts a hydrogen atom from methane to form a methyl radical and HCl; the methyl radical then reacts with another Cl2 molecule to form chloromethane and regenerate a chlorine radical, which continues the cycle:

   Cl• + CH4 -> CH3• + HCl

   CH3• + Cl2 -> CH3Cl + Cl•

(The regenerated Cl• can then attack another CH4 molecule, and the cycle repeats, so the overall reaction is "chain"-like: each initiation event can lead to many propagation cycles. Further substitution can similarly convert CH3Cl into CH2Cl2, CHCl3, and CCl4 with excess chlorine.) …