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23. Chemical energetics

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  1. 23.1 Lattice energy and Born-Haber cycles

    1. • Define/use:: (a) enthalpy change of atomisation, ΔHat; (b) lattice energy, ΔHlatt (the change from gas phase ions to solid lattice)

    2. • (a) define and use the term first electron affinity, EA: (b) explain the factors affecting the electron affinities of elements; (c) describe and explain the trends in the electron affinities of the Group 16 and Group 17 elements

    3. • Construct/use: Born–Haber cycles for ionic solids (limited to +1 and +2 cations, –1 and –2 anions)

    4. • Calculate: Born–Haber cycles

    5. • Explain, in qualitative terms, the effect of ionic charge and of ionic radius on the numerical magnitude of a lattice energy

  2. 23.2 Enthalpies of solution and hydration

    1. • Define/use: enthalpy change using hydration, ΔHhyd, and solution, ΔHsol

    2. • Construct/use: an energy cycle involving enthalpy change of solution, lattice energy and enthalpy change of hydration

    3. • Calculate: the energy cycles in 23.2.2

    4. • Explain, in qualitative terms, the effect of ionic charge and of ionic radius on the numerical magnitude of an enthalpy change of hydration

  3. 23.3 Entropy change, ΔS

    1. 23.3.1Terms: entropy, S, as the number of possible

      • Define: entropy, S, as the number of possible arrangements of the particles and their energy in a given system

    2. 23.3.2Predict/explain the sign of the entropy

      • Predict/explain: the sign of the entropy changes that occur: - (a) during a change in state, e.g. melting, boiling and dissolving (and their reverse) - (b) during a temperature change - (c) during a reaction in which there is a change in the number of gaseous molecules

    3. 23.3.3The entropy change for a reaction, ΔS

      • Calculate the entropy change for a reaction, ΔS, given the standard entropies, S ⦵ , of the reactants and products, ΔS ⦵ = ΣS ⦵: (products) – ΣS ⦵ (reactants) (use of ΔS ⦵ = ΔSsurr + ΔSsys is not required)

  4. 23.4 Gibbs free energy change, ΔG

    1. • State/use: the Gibbs equation ΔG ⦵ = ΔH ⦵ – TΔS ⦵

    2. • Perform calculations using the equation ΔG ⦵ = ΔH ⦵ – TΔS ⦵

    3. • State whether a reaction or process will be feasible by using the sign of ΔG

    4. • Predict the effect of temperature change on the feasibility of a reaction, given standard enthalpy and entropy changes