Calculate enthalpy

Question

The following reaction is exothermic.

N2(g)+H2(g)+3O2(g)=2HNO3(g) deltaH(1)=-270kj

calculate the enthalpy change for the reaction of the elements to form one mole of HNO3(g).

1/2N2(g)+1/2H2(g)+3/2 O2(g)=HNO3(g) DeltaH(2)=????kJ

Answer 1

N2(g)+H2(g)+3O2(g)=2HNO3(g) deltaH(1)=-270kj

By multiplying the all a compound with 0.5

We get

1/2N2(g)+1/2H2(g)+3/2 O2(g)=HNO3(g)

Also, multiply the delta H with 0.5

We get delta H = 270/2 Kj