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Thermodynamics (A-level only)
This A-level-only topic extends energetics into lattice enthalpy, entropy and thermodynamic feasibility.
9
Objectives
10
Flashcards
10
Questions
90 min
Study time
AqaA LevelChemistryPhysical chemistry
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9 objective pages available
Born-Haber cycles (A-level only)4 objectives
- Construct Born-Haber cycles for ionic compounds.
- Calculate lattice enthalpy from Born-Haber data.
- Compare experimental and theoretical lattice enthalpies.
- Use lattice enthalpy comparisons to infer covalent character.
Entropy and Gibbs free energy (A-level only)5 objectives
- Explain entropy as a measure of dispersal of energy or disorder.
- Calculate entropy changes from standard entropy data.
- Use ΔG = ΔH - TΔS to calculate Gibbs free energy change.
- Predict whether a reaction is feasible from Gibbs free energy.
- Explain why feasibility does not guarantee an observable reaction rate.
Key terms
Lattice EnthalpyBorn-Haber CycleEntropyGibbs Free EnergyStandard Entropy (S°)Gibbs Free Energy (G)Spontaneous ReactionThermodynamic EquilibriumGibbs Free Energy (ΔG)Entropy (ΔS)FeasibilityActivation Energy
Exam tips
- Draw the Born-Haber cycle clearly: When constructing a Born-Haber cycle, ensure that each step is clearly labeled with the corresponding enthalpy changes.
- Show all steps in calculations: Always show the governing relationship, substitution, units, and significant figures in your calculations.
Common mistakes
- Confusing lattice enthalpy with enthalpy of formation: Lattice enthalpy specifically refers to the energy associated with the formation of the ionic solid from gaseous ions, while enthalpy of formation refers to the overall energy change when forming the compound from its elements.
- Incorrect sign for lattice enthalpy: Remember that lattice enthalpy is typically negative for the formation of ionic solids, as energy is released.
Practice preview
- Which of the following steps is NOT included in the Born-Haber cycle for the formation of sodium chloride (NaCl)?
- Describe the significance of lattice enthalpy in the Born-Haber cycle.
- Calculate the lattice enthalpy of magnesium oxide (MgO) given the following data: Enthalpy of sublimation of Mg = +150 kJ/mol, Ionization energy of Mg = +738 kJ/mol, Dissociation energy of O2 = +498 kJ/mol, Electron affinity of O = -141 kJ/mol, Enthalpy of formation of MgO = -601 kJ/mol.
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