How do you calculate lattice energy?

Calculate the energy change in kJ for the formation of 0.69 mol of LiCl(s) given the following information..?

• Calculate the energy change in kJ for the formation of 0.69 mol of LiCl(s) given the following information: Li(g) → Li(s) : −159.4 KJ/mol 2Cl(g) → Cl2(g) : −243.358 KJ/mol Li+(g) + e− → Li(g) : −520 KJ/mol Electron affinity for Cl(g) : −349 KJ/mol Lattice energy for LiCl = −852 KJ/mol

• Answer:

  This is an application of the Born-Haber cycle calculation. The Enthalpy of formation (per mole) = The Enthalpy of vaporization (metal) [159.4 KJ/mol] plus the 1/2 Bond energy (non-metal) [243.358/2 KJ/mol] plus the Ionization energy (metal atom) [520 KJ/mol] minus Electron affinity (non-metal) [349 KJ/mol] minus Lattice energy (salt) [852 KJ/mol] Multiple this result (it should be a negative number) by the 0.69 moles of LiCl to get your answer. See the second reference below for a similar problem for NaCl.