What organic reaction type occurs when methane and chlorine are mixed in the presence of ultraviolet light? - Leaving Cert Chemistry - Question e - 2013

The reaction between methane and chlorine in the presence of ultraviolet light is characterized as a free radical substitution reaction.

Explanation

In this process, chlorine molecules dissociate under UV light to form reactive chlorine radicals. These radicals can abstract hydrogen atoms from methane, leading to the substitution of hydrogen atoms with chlorine.

The overall reaction can be summarized as follows:

1. Initiation:

   $Cl_2 \xrightarrow{UV} 2Cl \cdot$

2. Propagation:

   $CH_4 + Cl \cdot \rightarrow CH_3Cl + H \cdot$

   $H \cdot + Cl_2 \rightarrow HCl + Cl \cdot$

3. Termination: Combining radicals to stabilize.

This reaction results in the formation of chloromethane (CH₃Cl) and other chlorinated byproducts as further substitutions can occur.