①2H2O(g) = O2(g)+2H2(g) ΔH1
②Cl2(g)+H2(g) = 2HCl(g) ΔH2
③2Cl2(g)+2H2O(g) = 4HCl(g)+O2(g) ΔH3
则ΔH3与ΔH1、ΔH2间的关系正确的是 ( )