A-Level Chemistry Specification

Edexcel 9CH0

Section 13: Energetics II

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#13.1

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

#13.2

be able to define the terms:

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

#13.3

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

#13.4

know that lattice energy provides a measure of ionic bond strength

#13.5

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

#13.6

understand the meaning of polarisation as applied to ions

#13.7

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

#13.8

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

#13.9

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

#13.10

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

#13.11

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

i) lattice energy
ii) enthalpy change of hydration

#13.12

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

#13.13

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)

#13.14

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.

#13.15

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:

ΔStotal = ΔSsystem + ΔSsurroundings

#13.16

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

#13.17

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

\(ΔS_{\text{surroundings}} = - \dfrac{ΔH}{T}\)

#13.18

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 = ΔHTΔSsystem

#13.19

be able to use the equation ΔG = ΔHTΔSsystem to:

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

#13.20

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

#13.21

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

#13.22

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