For the gas-phase halogenation of methane CH (g) + X (g) → CH X(g) + HX(g)

CHEMISTRY · Subjective · A Level · Chemistry · Energetics · Energetics

Problem

For the gas-phase halogenation of methane CH4_4(g) + X2_2(g) → CH3_3X(g) + HX(g), where X is either Cl or Br, use the average bond energies below to determine ΔH for each halogen and identify which halogen gives a reaction enthalpy closest to zero. Provide both ΔH values (kJ mol−1^{-1}) and state your choice. Average bond energies (kJ mol−1^{-1}): C–H 413  Cl–Cl 243  Br–Br 193  C–Cl 328  C–Br 276  H–Cl 431  H–Br 366

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