OCR A Jun 2016 Paper 5 Q3

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This question is about four enthalpy changes, AD, that can be linked to the dissolving of potassium sulfate, K2SO4, in water. Name of enthalpy change Enthalpy change /kJ mol1 lattice enthalpy of potassium sulfate enthalpy change of solution of potassium sulfate enthalpy change of hydration of potassium ions enthalpy change of hydration of sulfate ions 1763 +24 320 (a) Define the term enthalpy change of hydration. Table 3.1[2] (b) The diagram below is an incomplete energy cycle linking the four enthalpy changes in Table 3.1. One of the four energy levels is missing. Include state symbols for all species. enthalpyOCR 2016<br />
 7 (i) Complete the energy cycle as follows. Add the missing energy level to the diagram. Add the species on all four energy levels. Add arrows to show the direction of the three missing enthalpy changes. Label these [5] enthalpy changes using the letters BD from Table 3.1. (ii) Calculate the enthalpy change of hydration of sulfate ions. H =kJ mol1 [1] (c) The entropy change of solution of K2SO4 is +225 J K1 mol1. (i) Suggest, in terms of the states of the particles involved, why this entropy change is positive.[1] (ii) Explain, using a calculation, why K2SO4 dissolves in water at 25 C, despite the enthalpy change of solution being endothermic.[3]OCR 2016 [Total: 12] Turn over<br />

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