Nitrogen oxides undergo many interesting reactions in the environment and in industry. Given the following information, calculate H for the overall equation:
2 NO2(g) + 1/2 O2(g) N2O5(s).
N2O5(s) 2 NO(g) + 3/2 O2(g), H = 223.7 kJ
NO(g) + 1/2 O2(g) NO2(g), H = -57.1 kJ
H = ______ kJ