①CH4(g)+O2(g)⇌CO(g)+H2(g)+H2O(g)△H=-321.5kJ/mol
②CH4(g)+H2O(g)⇌CO(g)+3H2(g)△H=+250.3kJ/mol
③CO(g)+2H2(g)⇌CH3OH(g)△H=-90.0kJ/mol
①+②得2CH4(g)+O2(g)⇌2CO(g)+4H2(g)△H=-71.5kj/mol
2CH4(g)+O2(g)⇌2CO(g)+4H2(g)=2CH3OH(g)△H=-71.5-90x2=-251.5kj/mol
所以CH4(g)+(1/2)O2(g)⇌CH3OH(g)△H=-125.75kj/mol
①②③是我在网上找的三个已知的热化学方程式。