Lattice energy and Born-Haber cyclesEdexcel International A Level Chemistry: Mind map

Exam questions on Lattice energy and Born-Haber cycles

1. A student constructs a Born–Haber cycle for sodium chloride using these standard enthalpy changes (kJ mol⁻¹): enthalpy change of formation of NaCl(s) −411; atomisation of sodium +107; first ionisation energy of sodium +496; atomisation of chlorine (per mole of Cl atoms) +122; first electron affinity of chlorine −349.
   Calculate the lattice energy of sodium chloride.2 marks
2. Magnesium chloride is used as a de-icing salt. A Born–Haber cycle is constructed for MgCl₂ using these standard enthalpy changes (kJ mol⁻¹): enthalpy change of formation of MgCl₂(s) −641; atomisation of magnesium +148; first ionisation energy of magnesium +738; second ionisation energy of magnesium +1451; atomisation of chlorine (per mole of Cl atoms) +122; first electron affinity of chlorine −349.
   Calculate the total enthalpy change for converting 1 mol of Mg(s) and 1 mol of Cl₂(g) into 1 mol of Mg²⁺(g) and 2 mol of Cl⁻(g).2 marks
3. A student compares two compounds that each contain a 1+ cation and a 1− anion. Lattice energies (kJ mol⁻¹), defined for formation of the solid from gaseous ions, are: sodium chloride, Born–Haber value −787 and value calculated from a purely ionic model −770; silver iodide, Born–Haber value −889 and value calculated from a purely ionic model −778.
   Calculate the difference between the Born–Haber and ionic-model lattice energies for each compound, and state which compound has the greater covalent character.3 marks