Calculate H for the dimerization of NO2 as shown below.?

Question

Consider the following data.
N2(g) + 2 O2(g) 2 NO2(g) DeltaH = 67.7 kJ
N2(g) + 2 O2(g) N2O4(g) DeltaH = 9.7 kJ
Calculate H for the dimerization of NO2 as shown below.
2 NO2(g) N2O4(g)

Answer 1

This problem can be solved by using the principle of Hess's Law:
N2(g) + 2O2(g) ==> 2 NO2(g) ∆H = 67.7 kJ...(1)
N2(g) + 2O2(g) ==> N2O4(g) ∆H = 9.7 kJ......(2)
(2) - (1):
2 NO2(g) ==> N2O4(g) ∆H = -58.0 kJ