A-Level Chemistry Edexcel 9CH0

be able to define lattice energy as the energy change when one mole of an ionic solid is formed from its gaseous ions

be able to define the terms:

i) enthalpy change of atomisation, Δ_atH ii) electron affinity

be able to construct Born-Haber cycles and carry out related calculations

know that lattice energy provides a measure of ionic bond strength

understand that a comparison of the experimental lattice energy value (from a Born-Haber cycle) with the theoretical value (obtained from electrostatic theory) in a particular compound indicates the degree of covalent bonding

understand the meaning of polarisation as applied to ions

know that the polarising power of a cation depends on its radius and charge

know that the polarisability of an anion depends on its radius and charge

be able to define the terms ‘enthalpy change of solution, Δ_solH’, and ‘enthalpy change of hydration, Δ_solH’

be able to use energy cycles and energy level diagrams to carry out calculations involving enthalpy change of solution, enthalpy change of hydration and lattice energy

understand the effect of ionic charge and ionic radius on the values of:

i) lattice energy ii) enthalpy change of hydration

understand that, since some endothermic reactions can occur at room temperature, enthalpy changes alone do not control whether reactions occur

know that entropy is a measure of the disorder of a system and that the natural direction of change is increasing total entropy (positive entropy change)

understand why entropy changes occur during:

i) changes of state ii) dissolving of a solid ionic lattice iii) reactions in which there is a change in the number of moles from reactants toproducts

*Students should be able to discuss typical reactions in terms of disorder andenthalpy change, including:

• dissolving ammonium nitrate crystals in water
• reacting ethanoic acid with ammonium carbonate
• burning magnesium ribbon in air
• mixing solid barium hydroxide, Ba(OH)₂.8H₂O, with solid ammonium chloride.*

understand that the total entropy change in any reaction is the entropy change in the system added to the entropy change in the surroundings, shown by the expression:

ΔS_total = ΔS_system + ΔS_surroundings

be able to calculate the entropy change for the system, ΔS_system, in a reaction, given the entropies of the reactants and products

be able to calculate the entropy change in the surroundings, and hence ΔS_total, using the expression:

$ΔS_{\text{surroundings}} = - \dfrac{ΔH}{T}$

know that the balance between the entropy change and the enthalpy change determines the feasibility of a reaction and is represented by the equation

ΔG = ΔH − TΔS_system

be able to use the equation ΔG = ΔH − TΔS_system to:

i) predict whether a reaction is feasible ii) determine the temperature at which a reaction is feasible

be able to use the equation ΔG = −RT ln K to show that reactions which are feasible in terms of ΔG have large values for the equilibrium constant and vice versa

understand why a reaction for which the ΔG value is negative may not occur in practice

know that reactions that are thermodynamically feasible may be inhibited by kinetic factors