Born-Haber cycles and lattice enthalpyAQA A-Level Chemistry: Mind map

Exam questions on Born-Haber cycles and lattice enthalpy

1. A student is constructing a Born–Haber cycle for magnesium oxide, MgO, starting from the elements in their standard states. The cycle contains the enthalpy of formation of MgO, the enthalpies of atomisation of magnesium and oxygen, the first and second ionisation energies of magnesium, the first and second electron affinities of oxygen, and the lattice enthalpy of MgO.
   The second electron affinity of oxygen is endothermic. Explain why.2 marks
2. Born–Haber data are used to find the lattice enthalpy of magnesium chloride, MgCl₂. Standard enthalpy changes (kJ mol⁻¹): enthalpy of formation of MgCl₂ = −641; enthalpy of atomisation of Mg = +148; first ionisation energy of Mg = +738; second ionisation energy of Mg = +1451; enthalpy of atomisation of Cl = +122 (per mole of Cl atoms); first electron affinity of Cl = −349.
   Write an equation, including state symbols, for the second ionisation energy of magnesium. Explain why it is larger than the first ionisation energy.2 marks
3. The enthalpy of formation of calcium oxide, CaO, is −635 kJ mol⁻¹. Other standard enthalpy changes (kJ mol⁻¹): atomisation of Ca = +178; first ionisation energy of Ca = +590; second ionisation energy of Ca = +1145; atomisation of oxygen, ½O₂(g) → O(g) = +249; first electron affinity of oxygen = −141. The enthalpy of lattice formation of CaO is −3401 kJ mol⁻¹.
   Calculate the second electron affinity of oxygen. Show your working.3 marks