Thermochemistry

 

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

 

             ΔH°rxn = ΣΔHf°(products) - ΣΔHf°(reactants)

             ΔH°rxn = [ΔHf°(N2(g)) + 4ΔHf°(H2O(g))] - [ΔHf°(N2O4(g)) + 4ΔHf°(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 = ΣΔHf°(products) - ΣΔHf°(reactants)

            ΔH°rxn = [ΔHf°(K2CO3(s)) + ΔHf°(H2O(g))] - [2ΔHf°(KOH(s)) + ΔHf°(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 = ΣΔHf°(products) - ΣΔHf°(reactants)

            ΔH°rxn = [(3/8)ΔHf°(S8(s)) +  2ΔHf°(H2O(g))] - [ΔHf°(SO2(g)) +  2ΔHf°(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 = ΣΔHf°(products) - ΣΔHf°(reactants)

            ΔH°rxn = [2ΔHf°(FeCl3(s)) +  3ΔHf°(H2O(g))] - [ΔHf°(Fe2O3(s)) +  6ΔHf°(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