①2H2(g)+CO(g)⇌CH3OH(g)△H=﹣90.8kJ•mol﹣1
②2CH3OH(g)⇌CH3OCH3(g)+H2O(g)△H=﹣23.5kJ•mol﹣1
③CO(g)+H2O(g)⇌CO2(g)+H2(g)△H=﹣41.3kJ•mol﹣1
总合成反应的热化学方程式为.