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Methane () reacts with chlorine in the presence of sunlight. If is replaced by deuterated methane ()Hydrogen Chemistry Question

Question

Methane ($CH_4$) reacts with chlorine in the presence of sunlight. If $CH_4$ is replaced by deuterated methane ($CD_4$) and tritium-substituted methane ($CT_4$), what is the correct order of the rate of the photochemical halogenation reaction?

Answer: A

💡 Solution & Explanation

Due to the kinetic isotopic effect, the bond dissociation enthalpy increases with isotopic mass ($H-H < D-D < T-T$). Therefore, the $C-H$ bond breaks much faster than the $C-D$ and $C-T$ bonds, making $CH_4$ the most reactive.

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