Which equation represents the standard enthalpy change of formation, \(\Delta H_f^\Theta \), of tetrachloromethane?

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

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

C.     \({\text{C(g)}} + {\text{2C}}{{\text{l}}_{\text{2}}}{\text{(g)}} \to {\text{CC}}{{\text{l}}_{\text{4}}}{\text{(g)}}\)

D.     \({\text{C(s)}} + {\text{2C}}{{\text{l}}_{\text{2}}}{\text{(g)}} \to {\text{CC}}{{\text{l}}_{\text{4}}}{\text{(l)}}\)

D

It is accepted that candidates should not have come across tetrachloromethane, \({\text{CC}}{{\text{l}}_{\text{4}}}\), it having been banned for many years. They were not expected to know that it is a liquid at room temperature and the question can be answered correctly without this knowledge. A standard enthalpy change of formation must start from the elements so only C and D are possible. Carbon is not a gas under standard conditions so answer C is excluded. Nearly 47% gave the correct answer.