Gce Model Questions Vol1 2025 Chemistry Question 20

Using a Born-Haber cycle, calculate the lattice energy of magnesium oxide and calcium oxide. The data are: \(\Delta_f H^\circ(\text{MgO}) = -601.6\ \text{kJ mol}^{-1}\), \(\Delta_f H^\circ(\text{CaO}) = -635\ \text{kJ mol}^{-1}\); sublimation enthalpies \(\Delta_{\text{sub}}H(\text{Mg}) = 148\ \text{kJ mol}^{-1}\), \(\Delta_{\text{sub}}H(\text{Ca}) = 178\ \text{kJ mol}^{-1}\); first ionisation energies \(IE_1(\text{Mg}) = 738\ \text{kJ mol}^{-1}\), \(IE_1(\text{Ca}) = 590\ \text{kJ mol}^{-1}\); electron affinity of oxygen \(EA(\text{O}) = -141\ \text{kJ mol}^{-1}\); O-O bond dissociation energy \(D(\text{O}=\text{O}) = 498\ \text{kJ mol}^{-1}\). Assume the lattice energy \(U\) is the only unknown in each cycle and give its value (in kJ mol\(^{-1}\)).