### Problem 8.65

Posted:

**Fri Jan 19, 2018 3:47 pm**Calculate the standard enthalpy of formation of dinitrogen pentoxide from the following data,

2NO(g) + O2(g) --> 2NO2(g) deltaH = -114.1 kJ

4NO2(g) + O2(g) --> 2N2O5(g) delta H = -110.2 kJ

and from the standard enthalpy of formation of nitric oxide, NO (which is 90.25 kJ).

I understand that the equation I'm looking for is N2(g) + 5/2O2(g) --> N2O5(g)

I don't know what I'm missing, but I don't understand how these equations form the one that I'm looking for, since I don't see N2 in either of the first two equations.

2NO(g) + O2(g) --> 2NO2(g) deltaH = -114.1 kJ

4NO2(g) + O2(g) --> 2N2O5(g) delta H = -110.2 kJ

and from the standard enthalpy of formation of nitric oxide, NO (which is 90.25 kJ).

I understand that the equation I'm looking for is N2(g) + 5/2O2(g) --> N2O5(g)

I don't know what I'm missing, but I don't understand how these equations form the one that I'm looking for, since I don't see N2 in either of the first two equations.