OCR A Jun 2014 Paper 5 Q1

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Answer all the questions. 1 BornHaber cycles can be used to calculate enthalpy changes indirectly. (a) The table below shows enthalpy changes for a BornHaber cycle involving potassium sulfide, K2S. Formation of potassium sulfide, K2S 1st electron affinity of sulfur 2nd electron affinity of sulfur Atomisation of sulfur 1st ionisation energy of potassium Atomisation of potassium Enthalpy change / kJ mol1 381 200 +640 +279 +419 +89 (i) The incomplete BornHaber cycle below can be used to determine the lattice enthalpy of potassium sulfide. In the boxes, write the species present at each stage in the cycle. Include state symbols for the species. 2K+(g) + S(g) + 2e 2K(s) + S(g) 2K(s) + S(s) K2S(s) [3]OCR 2014<br />
 (ii) Define, in words, the term lattice enthalpy.[2] (iii) Using the BornHaber cycle, calculate the lattice enthalpy of potassium sulfide. (b) Several ionic radii are shown below. lattice enthalpy =kJ mol1 [2] Ion Radius / pm Na+ 95 K+ 133 Rb+ 148 Cl181 Br 195 I 216 Predict the order of melting points for NaBr, KI and RbCl from lowest to highest. Explain your answer. Lowest melting pointHighest melting pointExplanation[3]OCR 2014 [Total: 10] Turn over<br />

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