Topic 23
Chemical
Energetics
Topic 23 covers lattice energy and the enthalpy change of atomisation, first electron affinity and its trends in Groups 16 and 17, Born–Haber cycles with calculations, the effect of ionic charge and radius on lattice energy, enthalpies of hydration and solution with energy cycles, entropy as the number of arrangements of particles and energy, the sign of entropy changes for changes of state, temperature and gas molecules, ΔS from standard entropies, and the Gibbs equation ΔG⦵ = ΔH⦵ − TΔS⦵ with feasibility and the effect of temperature.
Revision Notes
7 revision notes, in the order the specification teaches them.
Lattice Energy and Born–Haber Cycles
Lattice energy and Born–Haber cycles: definitions of atomisation, ionisation energy and electron affinity, constructing the cycle for NaCl and MgCl₂ and calculating the missing value.
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Lattice Energy Trends and Covalent Character
Lattice energy trends: charge and radius, the perfect ionic model against Born–Haber values, polarisation and covalent character in ionic compounds.
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Enthalpy of Solution and Hydration
Enthalpy of solution and hydration: definitions, energy cycles with lattice energy, worked calculations and the effect of ionic charge and radius.
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Entropy and the Direction of Change
Entropy: disorder and the dispersal of energy, entropy and temperature, changes of state, dissolving, gas moles and the natural direction of change.
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Calculating Entropy Changes
Entropy calculations: ΔS from standard entropies, units and worked examples.
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Feasibility, Gibbs Energy and Temperature
Feasibility: ΔG = ΔH − TΔS, the sign of ΔG, the effect of temperature and the temperature at which a reaction becomes feasible.
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Thermodynamic and Kinetic Stability
Thermodynamic and kinetic stability: feasible but slow reactions, activation energy and the limits of ΔG and ΔStotal predictions.
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Lattice Energy Map
Cambridge International AS & A Level Chemistry · Topic 23 Lattice energy
The whole section on one A4 page: atomisation, lattice energy, electron affinity trends, Born–Haber cycles, 2+ ions, and charge and radius.
Solution and Hydration Map
Cambridge International AS & A Level Chemistry · Topic 23 Enthalpies of solution and hydration
The whole section on one A4 page: enthalpies of solution and hydration, the solution cycle, energy level diagrams, charge and radius, and the Group 2 trends.
Entropy and Gibbs Free Energy Map
Cambridge International AS & A Level Chemistry · Topic 23 Entropy and Gibbs free energy
The whole section on one A4 page: entropy, state and temperature, the sign of ΔS, ΔS and ΔG, temperature and feasibility, and ΔG against T.
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23.1.1
- b
define and use the term lattice energy, ΔHlatt (the change from gas phase ions to solid lattice)
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23.1.2
23.1.3
- 23.1.3
construct and use Born–Haber cycles for ionic solids (limited to +1 and +2 cations, –1 and –2 anions)
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23.1.4
23.1.5
23.2.1
23.2.2
- 23.2.2
construct and use an energy cycle involving enthalpy change of solution, lattice energy and enthalpy change of hydration
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23.2.3
23.2.4
23.3.1
- 23.3.1
define the term entropy, S, as the number of possible arrangements of the particles and their energy in a given system
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23.3.2
- a
predict and explain the sign of the entropy changes that occur during a change in state, e.g. melting, boiling and dissolving (and their reverse)
Revise - c
predict and explain the sign of the entropy changes that occur during a reaction in which there is a change in the number of gaseous molecules
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23.3.3
- 23.3.3
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)
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23.4.1
23.4.2
23.4.3
23.4.4
- 23.4.4
predict the effect of temperature change on the feasibility of a reaction, given standard enthalpy and entropy changes
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