Fig. 2.1 shows an incomplete energy cycle. [Figure 2.1]

1. (a)Predict and explain the variation in enthalpy change of hydration for the ions Na⁺, Mg²⁺ and Al³⁺.[3]
2. (b)(i)Complete line C on Fig. 2.1. Include state symbols.[1]
3. (b)(ii)Use both words and symbols to identify change 2 on Fig. 2.1. Use changes 1 and 3 as examples of how this should be done.[2]
4. (b)(iii)Calculate a value for the lattice energy of magnesium chloride, ΔHlatt MgCl₂(s), by selecting and using appropriate data from Table 2.1. Table 2.1 energy change value/kJ mol⁻¹ enthalpy change of solution of magnesium chloride -155 enthalpy change of formation of magnesium chloride -642 first ionisation energy of magnesium +736 second ionisation energy of magnesium +1450 electron affinity of chlorine -349 enthalpy change of hydration of Mg²⁺ -1920 enthalpy change of hydration of Cl⁻ -364 ∆Hlatt MgCl₂(s) = kJ mol⁻¹[3]
5. (c)Define entropy.[1]
6. (d)At 25°C the enthalpy change of solution of compound Z is +26kJmol⁻¹. The entropy change of solution of Z at the same temperature is +52JK⁻¹mol⁻¹. Calculate the value of the Gibbs free energy change, ΔG, for the solution of Z at 25 °C. ΔG = kJ mol⁻¹[2]
7. (e)(i)Use your answer to (d) to predict whether or not Z is soluble in water at 25°C. Explain your answer.[1]
8. (e)(ii)Predict whether Z becomes more or less soluble as the water is heated from 25°C to 95°C. Explain your answer.[1]

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