已知反应:①H2(g)+ O2(g)=H2O(g) ΔH1 ② N2(g)+O2(g)=NO2(g) ΔH2 ③ N2(g)+ H2(g)=NH3(g) ΔH3 则反应2NH3(g)+O2(g)=2NO2(g)+3H2O(g)的ΔH为
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