Question

Use the data in the table above to calculate an approximate ΔH∘ in kilojoules for the synthesis of hydrazine from ammonia:

Answer 1

DeltaH formation = deltaH of broken bonds - deltaH of formed bonds

Broken bonds: tiple bond N-N and H-H bond
Formed bonds: N-H and N-N bonds

You also have to take note of the molar coefficients

deltaH formation =  [(N≡N) + 2 * (H-H)] - [4 * (N-H) + (N-N)] 
                           = (945 + 2*436) - (4*390 + 240)
                            = 17 kJ/mol

The answer is 17 kJ/mol.