GivenN2g+3H2g = 2NH3g;  ∆H0=-22 kcal. The standard enthalpy of formation of NH3 gas is

∆H0=∑  n∆Hfproduct0 - ∑  n∆Hfreactant0 22Kcal=2∆Hf0NH3 - ∆Hf0N2+3∆Hf0H2, 22Kcal=2 ∆Hf0NH3 - 0+0 So, ∆Hf0NH3 = -11 kcal