OCR A Jun 2012 Paper 5 Q1

Answers available below

Answer all the questions. Lattice enthalpy can be used as a measure of ionic bond strength. Lattice enthalpies can be determined indirectly using BornHaber cycles. The table below shows the enthalpy changes that are needed to determine the lattice enthalpy of lithium fluoride, LiF. enthalpy change 1st electron affinity of fluorine 1st ionisation energy of lithium atomisation of fluorine atomisation of lithium formation of lithium fluoride energy / kJ mol1 328 +520 +79 +159 616 (a) Define the term lattice enthalpy.[2] (b) The diagram below shows an incomplete BornHaber cycle that would allow the lattice enthalpy of lithium fluoride to be determined. (i) On the four dotted lines, add the species present, including state symbols.Li+(g) + F(g)LiF(s)OCR 2012 [4]<br />
 (ii) Calculate the lattice enthalpy of lithium fluoride. lattice enthalpy =kJ mol1 [2] (c) The change that produces lattice enthalpy is spontaneous but has a negative entropy change. Why is this change able to take place spontaneously?[1] (d) The lattice enthalpies of sodium fluoride, sodium chloride and magnesium fluoride are shown below. compound lattice enthalpy / kJ mol1 sodium fluoride sodium chloride magnesium fluoride 918 780 2957 Explain the differences between these lattice enthalpies. In your answer, your explanation should show how different factors affect lattice enthalpy.[3]OCR 2012 [Total: 12] Turn over<br />

Show answer