Which of the following correctly describes the nature of the transition state of the rate-determining step of the free-radical bromination of methane? a. the transition state resembles the products more than the reactants b. the transition state equally resembles products and reactants c. the transition state resembles the reactants more than the products

the transition state will resemble the products more than the reactants

Explanation:

Since the free-radical bromination of methane involves the following reactions

Br₂ → 2 Br•  , ΔH⁰ (per mole) = +192 kJ , Ea (per mole) = + 192 kJ

CH₄ +Br•   → CH₃• + HBr  , ΔH⁰ (per mole) = +67 kJ , Ea (per mole) = + 75 kJ

CH₃• +Br₂  → CH₃Br  + Br•  , ΔH⁰ (per mole) = -101 kJ , Ea (per mole) = -4 kJ

without considering the Br dissociation (initiation reaction) the rate-determining step is the second equation ( highest Ea) .

Then since the reaction is endothermic (ΔH⁰ (per mole) = +67 kJ) , the transition state will resemble the products more than the reactants ( Hammond postulate)

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