Question

【題目】已知熱化學方程式：

① C2H2(g) +O2(g) = 2CO2(g)＋H2O(l) ΔH1＝-1301.0 kJmol-1

② C(s)+ O2(g) = CO2(g) △H2＝-393.5 kJmol-1

③ H2(g)+O2(g) = H2O(l) △H3 = -285.8 kJ·mol-1

則反應④ 2C(s)+ H2(g) = C2H2(g)的△H為( )

A.+228.2 kJ·mol-1B.-228.2 kJ·mol-1

C.+1301.0 kJ·mol-1D.+621.7 kJ·mol-1

Answer 1

【答案】A

【解析】

已知：① C2H2(g) +O2(g) = 2CO2(g)＋H2O(l) ΔH1＝-1301.0 kJmol-1

② C(s)+ O2(g) = CO2(g) △H2＝-393.5 kJmol-1

③ H2(g)+O2(g) = H2O(l) △H3 = -285.8 kJ·mol-1

根據蓋斯定律②×2+③-①可得2C(s)+ H2(g) = C2H2(g)的△H=-393.5 kJmol-1×2+(-285.8 kJ·mol-1)-(-1301.0 kJmol-1)=+228.2 kJ·mol-1，故答案為A。