Solution: Calculate ΔH for the reaction N2H4 (l) + O2 (g) → N2 (g) + 2H2O (l)given the following data2 NH3 (g) + 3N2O (g) → 4N2(g) + 3H2O (l)      ΔH = -1010 kJN2O (g) + 3 H2 (g) → N2H4 (l) + H2O (l)           ΔH = -317 kJ2NH3 (g) + 1/2 O2 (g) → N2H4 (l) + H2O (l)       ΔH = -143 kJH2 (g) + 1/2 O2 (g) → H2O (l)                            ΔH  = -286 kJ

We’re being asked to determine the enthalpy change (ΔH_rxn) for the chemical reaction:

N₂H₄ (l) + O₂ (g) → N₂ (g) + 2 H₂O (l)

We can use Hess’s Law to determine the enthalpy change of the overall reaction from the given reactions:

1. 2 NH₃ (g) + 3 N₂O (g) → 4 N₂(g) + 3 H₂O (l)      ΔH = -1010 kJ

2. N₂O (g) + 3 H₂ (g) → N₂H₄ (l) + H₂O (l)              ΔH = -317 kJ

3. 2 NH₃ (g) + 1/2 O₂ (g) → N₂H₄ (l) + H₂O (l)        ΔH = -143 kJ

4. H₂ (g) + 1/2 O₂ (g) → H₂O (l)                               ΔH  = -286 kJ

We now need to find a combination of reactions that when added up, gives us the overall reaction.