某些化学键键能数据如下：化学键 H—H Cl—C

某些化学键键能数据如下：化学键 H—H Cl—Cl H—Cl 键能/ kJ·mol －1 436 243 431

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C
ΔH＝反应物的键能之和－生成物的键能之和，
H₂(g)＋
Cl₂(g)=HCl(g)的ΔH＝(436 kJ·mol^－¹＋243 kJ·mol^－¹)/2－431 kJ·mol^－¹＝－91.5 kJ·mol^－¹，所以，A项对，C项错；B项反应的ΔH＝436 kJ·mol^－¹＋243 kJ·mol^－¹－2×431 kJ·mol^－¹＝－183 kJ·mol^－¹，对；D项反应的ΔH＝2×431 kJ·mol^－¹－(436 kJ·mol^－¹＋243 kJ·mol^－¹)＝＋183 kJ·mol^－¹，对。