Calculate the standard reaction enthalpy for the oxidation of nitric acid to nitrogen dioxide, 2NO(g) + O2(g) ----> 2NO2(g) from the standard reaction enthalpies of: N2(g) + O2 ------> 2NO(g) DH = +180.5 kJ x mol-1 2NO2 (g) --------> N2(g) + 2O2(g) DH = -66.4 kJ x mol-1