Question
Calculate the lattice enthalpy of KCl crystal from the following data:
Sublimation enthalpy of pottasium (K) = +89 kJ mol-1
Dissociation enthalpy of 
= +122 kJ mol-1
Ionisation enthalpy of K(g) +425 kJ mol-1
Electron gain enthalpy of Cl(g) = -355 kJ mol-1
Enthalpy of formation of 
Solution
Using Born-Haber cycle for KCl,
Substituting the values we have,
The reverse of the above equation i.e.
Hence the lattice enthalpy of KCl = +719 kJ mol-1
