(1)①H2(g)+Cl2(g)═2HCl(g)△H=-184kJ/mol
②4HCl(g)+O2(g)
2Cl2(g)+2H2O(g)△H=-115.6kJ/molCuO/CuCl2
400℃
根据盖斯定律①×2+②得:2H2(g)+O2(g)=2H2O(g)△H=-483.6 kJ/mol;
故答案为:2H2(g)+O2(g)=2H2O(g)△H=-483.6 kJ/mol;
(2)2H2(g)+O2(g)=2H2O(g)△H=-483.6 kJ/mol,△H=断裂化学键吸收的能量-形成化学键放出的能量=2×436KJ+498KJ-4×H-O=-483.6 kJ,则得到H-O的键能=463.4kJ;
故答案为:463.4;