Chlorination of methane is one industrial route to methyl chloride, an important feedstock for silicone production. The overall gas‐phase reaction is
CH4(g) + Cl2(g) → CH3Cl(g) + HCl(g)
Average bond energies (298 K):
• C–H 413 kJ mol⁻¹
• C–Cl 327 kJ mol⁻¹
• Cl–Cl 242 kJ mol⁻¹
• H–Cl 431 kJ mol⁻¹
Answer the following, showing your work.
(a) For one mole of reaction as written, enumerate all bonds broken and all bonds formed.
(b) Calculate the enthalpy change, ΔH, for the reaction.
(c) The chlorination is typically initiated by ultraviolet light. Based on the sign and magnitude of ΔH you calculated, discuss why external energy input (light) is required to start but not sustain the reaction.