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How does methane react with chlorine in a substitution reaction?

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combustion — chemical reaction Log burning in a fire. Burning wood is an example of a chemical reaction in which wood in the presence of heat and oxygen is transformed into carbon dioxide, water vapor, and ash.

The reaction between methane and chlorine is a free-radical substitution reaction initiated by light, typically ultraviolet irradiation. The overall chemical equation is:1

$C H_{4} (g) + C l_{2} (g) + h ν \to C H_{3} C l (g) + H C l (g)$

This process functions as a chain reaction consisting of three distinct phases:1

Chain-initiation: The chlorine molecule absorbs energy and undergoes homolytic cleavage to produce two chlorine radicals ( $\cdot C l$ ).12
Chain-propagation: A chlorine radical collides with a methane molecule to form a methyl radical ( $\cdot C H_{3}$ ) and hydrogen chloride ( $H C l$ ). The methyl radical then reacts with a chlorine molecule to produce chloromethane ( $C H_{3} C l$ ) and a new chlorine radical, which sustains the cycle.1
Chain-termination: The reaction concludes when radicals combine, such as two methyl radicals forming ethane or a methyl radical combining with a chlorine radical to form chloromethane.1

This is classified as a radical substitution reaction, distinct from nucleophilic or electrophilic substitution, because it involves highly reactive species containing unpaired electrons.32