Thermochemistry

 72) (a) N₂O₄(g) + 4H₂(g) N₂(g) + 4H₂O(g)

             ΔH°_rxn = ΣΔH_f°(products) - ΣΔH_f°(reactants)

             ΔH°_rxn = [ΔH_f°(N₂(g)) + 4ΔH_f°(H₂O(g))] - [ΔH_f°(N₂O₄(g)) + 4ΔH_f°(H₂(g))]

             ΔH°_rxn = [0 + 4 mol H₂O(g) x -241.82 kJ/1 mol H₂O(g)] - [1 mol N₂O₄(g) x 9.66 kJ/1 mol N₂O₄(g) + 0] = -976.94 kJ

       (b) 2KOH(s) + CO₂(g) K₂CO₃(s) + H₂O(g)

            ΔH°_rxn = ΣΔH_f°(products) - ΣΔH_f°(reactants)

            ΔH°_rxn = [ΔH_f°(K₂CO₃(s)) + ΔH_f°(H₂O(g))] - [2ΔH_f°(KOH(s)) + ΔH_f°(CO₂(g))]

            ΔH°_rxn = [1 mol K₂CO₃(s) x -1150.18 kJ/1 mol K₂CO₃(s) + mol H₂O(g) x -241.82 kJ/1 mol H₂O(g)] -

[2 mol KOH(s) x -424.7 kJ/1 mol KOH(s) + 1 mol CO₂(g) x -393.5 kJ/1 mol CO₂(g)] = -149.1 kJ

       (c) SO₂(g) + 2H₂S(g) (3/8)S₈(s) + 2H₂O(g)

            ΔH°_rxn = ΣΔH_f°(products) - ΣΔH_f°(reactants)

            ΔH°_rxn = [(3/8)ΔH_f°(S₈(s)) +  2ΔH_f°(H₂O(g))] - [ΔH_f°(SO₂(g)) +  2ΔH_f°(H₂S(g))]

            ΔH°_rxn = [0 + 2 mol H₂O(g) x -241.82 kJ/1 mol H₂O(g)] -

[1 mol SO₂(g) x -296.9 kJ/1 mol SO₂(g) + 2 mol H₂S(g) x -20.17 kJ/1 mol H₂S(g)] = -146.4 kJ

       (d) Fe₂O₃(s) + 6HCl(g) 2FeCl₃(s) + 3H₂O(g)

            ΔH°_rxn = ΣΔH_f°(products) - ΣΔH_f°(reactants)

            ΔH°_rxn = [2ΔH_f°(FeCl₃(s)) +  3ΔH_f°(H₂O(g))] - [ΔH_f°(Fe₂O₃(s)) +  6ΔH_f°(HCl(g))]

            ΔH°_rxn = [2 mol Fe₂O₃(s) x -400 kJ/1 mol Fe₂O₃(s) + 3 mol H₂O(g) x -241.82 kJ/1 mol H₂O(g)] -

[1 mol Fe₂O₃(s) x -822.16 kJ/1 mol Fe₂O₃(s) + 6 mol HCl(g) x -92.30 kJ/1 mol HCl(g)] = -150 kJ