4.
已知:\(\rm{P_{4}(g)+6Cl_{2}(g)===4PCl_{3}(g)}\) \(\rm{Δ}\) \(\rm{H}\)\(\rm{=}\) \(\rm{a}\)\(\rm{kJ·mol^{-1}}\),\(\rm{P_{4}(g)+10Cl_{2}(g)===4PCl_{5}(g)}\) \(\rm{Δ}\) \(\rm{H}\)\(\rm{=}\) \(\rm{b}\)\(\rm{kJ·mol^{-1}}\),\(\rm{P_{4}}\)具有正四面体结构,\(\rm{PCl_{5}}\)中\(\rm{P—Cl}\)键的键能为 \(\rm{c}\)\(\rm{kJ·mol^{-1}}\),\(\rm{PCl_{3}}\)中\(\rm{P—Cl}\)键的键能为 \(\rm{1.2}\) \(\rm{c}\)\(\rm{kJ·mol^{-1}}\)。下列叙述正确的是\(\rm{(}\) \(\rm{)}\)