Which process represents the C–Cl bond enthalpy in tetrachloromethane?

A.     \({\text{CC}}{{\text{l}}_{\text{4}}}{\text{(g)}} \to {\text{C(g)}} + {\text{4Cl(g)}}\)

B.     \({\text{CC}}{{\text{l}}_4}({\text{g)}} \to {\text{CC}}{{\text{l}}_3}({\text{g)}} + {\text{Cl(g)}}\)

C.     \({\text{CC}}{{\text{l}}_4}({\text{l)}} \to {\text{C(g)}} + 4{\text{Cl(g)}}\)

D.     \({\text{CC}}{{\text{l}}_4}({\text{l)}} \to {\text{C(s)}} + 2{\text{C}}{{\text{l}}_2}({\text{g)}}\)

B

The difficulty index for this question was 35% with both answers A and D providing very attractive discriminators. Though the bond enthalpy can be determined in terms of the change in response A, candidates should have realised that the magnitude of the associated enthalpy change would be approximately four times greater than that required to break a single C-Cl bond.