Question

Using Hess’s Law with the following data:
N2(g) + O2(g) = 2NO(g) Del(H) = 180.7kj
2NO(g) + O2(g) = 2NO2(g) Del(H)= -113.1kj
2N2O(g) = 2N2(g)+ O2(g) Del(H)=-163.2kj
Calculate Del(H) for the reaction:
N2O(g) + NO2(g) = 3NO(g)

Answer 1

Add eqn 1 to 1/2 the reverse of eqn 2 + 1/2 eqn 3 to obtain the final equation you want. Then add the delta H values EXCEPT if you take 1/2 the equation also take 1/2 dH and if you reverse an equation then you change the sign of dH.