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

What these 14 flashcards ask

  • Define the enthalpy change of atomisation.
  • Define the first electron affinity.
  • Define lattice energy (as used in this course).
  • Write the equation for the lattice energy of NaCl.
  • Is atomisation exothermic or endothermic?
  • Why is the second electron affinity of oxygen endothermic?
  • What is a Born–Haber cycle?
  • Give the expression for lattice energy from a Born–Haber cycle.
  • What must you change in the cycle for MgCl₂ compared with NaCl?
  • What does the theoretical lattice energy assume?
  • What does an experimental value more exothermic than the theoretical one show?
  • Define polarisation of an anion.
  • Which anion is more easily polarised, Cl⁻ or I⁻?
  • Calculate the lattice energy of KCl: ΔfH −437, atomisation of K +89, IE of K +419, atomisation of Cl +122, EA of Cl −349 (kJ mol⁻¹).

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
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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).