寫出下列反應(yīng)的標(biāo)準(zhǔn)平衡常數(shù)表達(dá)式 (1)N2(g)+3H2(g)=2NH3(g) (2)CH4(g)+2O2(g)=CO2(g)+2H2O(l) (3)CaCO3(s)=CaO(s)+CO2(g)