Lattice energy and Born-Haber cycles
Cambridge A-Level Chemistry (9701) · Unit 23: Chemical energetics · 8 flashcards
Lattice energy and Born-Haber cycles is topic 23.1 in the Cambridge A-Level Chemistry (9701) syllabus , positioned in Unit 23 — Chemical energetics , alongside Enthalpies of solution and hydration. In one line: The enthalpy change of atomisation is the enthalpy change when one mole of gaseous atoms is formed from its element in its standard state under standard conditions.
Marked as A2 Level: examined at A Level in Paper 4 (A Level Structured Questions) and Paper 5 (Planning, Analysis and Evaluation). It is not tested on the AS-only papers (Papers 1, 2 and 3).
The deck below contains 8 flashcards — 2 definitions, 5 key concepts and 1 calculation — covering the precise wording mark schemes reward. Use the 2 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
The term 'enthalpy change of atomisation' (ΔHₐt)
The enthalpy change of atomisation is the enthalpy change when one mole of gaseous atoms is formed from its element in its standard state under standard conditions.
What the Cambridge 9701 syllabus says
Official 2025-2027 spec · A2 LevelThese are the exact learning outcomes Cambridge sets for this topic. The candidate is expected to be able to do each of these on the relevant paper.
- define and use the terms: (a) enthalpy change of atomisation, ΔHat (b) lattice energy, ΔHlatt (the change from gas phase ions to solid lattice)
- construct and use Born–Haber cycles for ionic solids
- carry out calculations involving Born–Haber cycles
- explain, in qualitative terms, the effect of ionic charge and of ionic radius on the numerical magnitude of a lattice energy
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9701 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Lattice energy and Born-Haber cycles
- › Remember that enthalpy of formation is zero for elements, but atomisation requires finite energy to break covalent bonds in diatomic molecules.
- › Do not use a Data Booklet unless specifically instructed; use the values provided in the question paper for calculations.
- › Always ensure ΔS is converted from J K⁻¹ mol⁻¹ to kJ K⁻¹ mol⁻¹ to match the units of ΔH in the Gibbs equation.
- › Always calculate moles for both reactants to identify the limiting reagent before proceeding to gas volume calculations using the balanced equation.
- › Ensure definitions include specific molar quantities; neutralisation is the enthalpy change when one mole of water is formed from an acid-alkali reaction.
Define the term 'enthalpy change of atomisation' (ΔHₐt).
The enthalpy change of atomisation is the enthalpy change when one mole of gaseous atoms is formed from its element in its standard state under standard conditions.
Define 'lattice energy' (ΔHlatt) for an ionic solid.
Lattice energy is the enthalpy change when one mole of a solid ionic compound is formed from its gaseous ions under standard conditions. It is always exothermic (negative value) because energy is released when ions come together to form a stable lattice.
What is the purpose of a Born-Haber cycle?
A Born-Haber cycle is an application of Hess's Law to calculate the lattice energy of an ionic compound. It links the enthalpy change of formation of an ionic solid with other enthalpy changes (
Outline the steps required to construct a Born-Haber cycle for NaCl.
1. Start with elements in their standard states: Na(s) + 1/2Cl₂(g). 2. Atomisation: Na(g) + Cl(g). 3. Ionisation: Na⁺(g) + Cl(g) + e⁻. 4. Electron affinity: Na⁺(g) + Cl⁻(g). 5. Lattice formation: NaCl(s).
Given the following enthalpy changes, calculate the lattice energy of MgO: ΔHformation = -602 kJ/mol, ΔHat (Mg) = +148 kJ/mol, IE₁ (Mg) = +738 kJ/mol, IE₂ (Mg) = +1451 kJ/mol, ΔHat (O) = +249 kJ/mol, EA₁ (O) = -141 kJ/mol, EA₂ (O) = +798 kJ/mol.
Using the Born-Haber cycle: ΔHformation = ΔHat(Mg) + IE₁ + IE₂ + ΔHat(O) + EA₁ + EA₂ + ΔHlatt. Therefore, ΔHlatt = ΔHformation - [ΔHat(Mg) + IE₁ + IE₂ + ΔHat(O) + EA₁ + EA₂] = -602 - [148 + 738 + 1451 + 249 - 141 + 798] = -3845 kJ/mol
How does ionic charge affect the magnitude of lattice energy?
Lattice energy is directly proportional to the product of the ionic charges. Higher ionic charges lead to stronger electrostatic attractions and thus a more negative (larger magnitude) lattice energy.
How does ionic radius affect the magnitude of lattice energy?
Lattice energy is inversely proportional to the sum of the ionic radii. Larger ionic radii lead to weaker electrostatic attractions (ions are further apart) and thus a less negative (smaller magnitude) lattice energy.
Explain why the second electron affinity of oxygen is endothermic.
The second electron affinity of oxygen is endothermic because a negatively charged O⁻ ion is forced to accept another negatively charged electron. This requires energy to overcome the electrostatic repulsion between the existing negative charge and the incoming electron.
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Lattice energy and Born-Haber cycles sits alongside these A-Level Chemistry decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Lattice energy and Born-Haber cycles deck
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