Question

【题目】已知：①CO2(g)+2H2(g)═ CH3OH(g)+O2(g) △H=+192.9kJ/mol

②H2(g)+ O2(g)═H2O(l) △H=285.8kJ/mol

则CH3OH(g) +O2(g)═CO2(g)+2H2O(l)的△H为( )

A. +478.7kJ/mol

B. 764.5kJ/mol

C. 478.7kJ/mol

D. +764.5kJ/mol

Answer 1

【答案】B

【解析】根据盖斯定律，将①-②×2得：CO2(g)+2H2O(l)= CH3OH(g) +O2(g)，然后分析计算。

①CO2(g)+2H2(g)═ CH3OH(g)+O2(g) △H=+192.9kJ/mol，②H2(g)+ O2(g)═H2O(l) △H=285.8kJ/mol，根据盖斯定律，将①-②×2得：CO2(g)+2H2O(l)= CH3OH(g) +O2(g) △H=(+192.9kJ/mol)-(285.8kJ/mol)×2=+764.5kJ/mol，则CH3OH(g) +O2(g)═CO2(g)+2H2O(l) △H=-764.5kJ/mol，故选B。