Answer all the questions in the spaces provided. (d) (i) The equation for the formation of a gaseous sulfate ion is shown. S(s) + 2O2(g) + 2e¯ → SO42-(g) ΔΗ = ΔΗ of SO42-(g) Calculate the standard enthalpy change of formation, ΔΗ, of SO42-(g). It may be helpful to draw a labelled energy cycle. Use relevant data from Table 1.1 in your calculations. Table 1.1 energy change value/kJmol-1 lattice energy of barium sulfate, BaSO4(s) -2469 standard enthalpy change of formation of barium sulfate -1473 standard enthalpy change of atomisation of barium +180 first ionisation energy of barium +503 second ionisation energy of barium +965 standard enthalpy change of atomisation of sulfur +279 standard enthalpy change for S(g) → S²-(g) +440 standard enthalpy change for O(g) → O2-(g) +657 O=O bond energy +496 (e) The reaction of solid hydrated barium hydroxide, Ba(OH)2•8H2O, with ammonium salts is endothermic. Ba(OH)2 8H2O(s) + 2NH4NO3(s) → 2NH3(g) + Ba(NO3)2(s) + 10H2O(1) ∆H = +132kJmol-1 AS = +616 JK-1 mol-1 (ii) Barium hydroxide reacts readily with ammonium chloride on mixing at room temperature. Ba(OH)2 8H2O(s) + 2NH4Cl(s) → 2NH3(g) + BaCl2•2H2O(s) + 8H2O(I) ∆H = +133kJ mol-1 Some relevant standard entropies are given in Table 1.2. Table 1.2 substance S/JK-1 mol-1 Ba(OH)2 8H2O(s) NH4Cl(s) 427 95 NH3(g) 192 BaCl2 2H2O(s) 203 H₂O(I) 70

1. (a)The solubility of the Group 2 sulfates decreases down the group. Explain this trend.[3]
2. (b)Describe what is observed when magnesium and barium are reacted separately with an excess of dilute sulfuric acid. magnesium barium[1]
3. (c)The solubility product, Ksp, of BaSO4 is 1.08 × 10–10 mol² dm-6 at 298 K. Calculate the solubility of BaSO4 in g per 100 cm³ of solution. solubility of BaSO4 = ... g per 100 cm³ of solution[2]
4. (d)(i)The equation for the formation of a gaseous sulfate ion is shown. S(s) + 2O2(g) + 2e¯ → SO42-(g) ΔΗ = ΔΗ of SO42-(g) Calculate the standard enthalpy change of formation, ΔΗ, of SO42-(g). It may be helpful to draw a labelled energy cycle. Use relevant data from Table 1.1 in your calculations. ∆H of SO42-(g) = ... kJ mol-1[3]
5. (d)(ii)Suggest how the lattice energy of BaSO4(s) differs from the lattice energy of Cs₂SO₄(s). Explain your answer.[2]
6. (e)(i)Calculate the minimum temperature at which the reaction of Ba(OH)2•8H2O with NH4NO3 becomes feasible. Show all your working. Ba(OH)2 8H2O(s) + 2NH4NO3(s) → 2NH3(g) + Ba(NO3)2(s) + 10H2O(1) ∆H = +132kJmol-1 AS = +616 JK-1 mol-1 temperature = ... °C[2]
7. (e)(ii)Barium hydroxide reacts readily with ammonium chloride on mixing at room temperature. Ba(OH)2 8H2O(s) + 2NH4Cl(s) → 2NH3(g) + BaCl2•2H2O(s) + 8H2O(I) ∆H = +133kJ mol-1 Some relevant standard entropies are given in Table 1.2. Calculate the standard Gibbs free energy change, AG°, for this reaction at 25°C. AG = ... kJ mol-1[3]

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