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OCR A Level Chemistry A – Module 5 Physical Chemistry and Transition Elements

5.2.1
Lattice Enthalpy

Section 5.2.1 covers lattice enthalpy as a measure of the strength of ionic bonding, the construction of Born–Haber cycles for simple ionic solids such as NaCl and MgCl₂ and the related calculations, the enthalpy changes of solution and hydration with their enthalpy cycles, and the qualitative effect of ionic charge and radius on lattice enthalpy and on hydration enthalpy.

Exam Paper
Paper 1 & 3
H432/01 and H432/03
Learning Outcomes
5.2.1 (a) – (e)
5 learning outcomes
Topic Parts
3 pages
Revision notes available
Exam Board
OCR A
H432 (2015 onwards)

Revision Notes

Work through 5.2.1 Lattice Enthalpy in a structured sequence.

Hess’s law for ionic solids
Born–Haber
Cycles
1
Available

Lattice Enthalpy and Born–Haber Cycles

Lattice enthalpy 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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Charge density
Polarisation and
Covalent Character
2
Available

Lattice Enthalpy Trends and Covalent Character

Lattice enthalpy trends: charge and radius, the perfect ionic model against Born–Haber values, polarisation and covalent character in ionic compounds.

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Lattice broken, ions hydrated
Solution and
Hydration
3
Available

Enthalpy of Solution and Hydration

Enthalpy of solution and hydration: definitions, energy cycles with lattice enthalpy, worked calculations and the effect of ionic charge and radius.

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Specification Coverage

5.2.1 Lattice Enthalpy – OCR A Level Chemistry A

The following OCR A learning outcomes state what candidates should be able to do. Wording is taken from the OCR A Level Chemistry A (H432) specification.

5.2.1 Lattice enthalpy

5.2.1(a)
i
explanation of the term lattice enthalpy (formation of 1 mol of ionic lattice from gaseous ions, ΔLEH)
ii
use of lattice enthalpy as a measure of the strength of ionic bonding in a giant ionic lattice (see also 2.2.2 b–c)
5.2.1(b)
(i)
use of the lattice enthalpy of a simple ionic solid (e.g. NaCl, MgCl₂) and relevant energy terms for the construction of Born–Haber cycles
(ii)
use of the lattice enthalpy of a simple ionic solid (e.g. NaCl, MgCl₂) and relevant energy terms for related calculations
5.2.1(c)
(i)
explanation and use of the term enthalpy change of solution (dissolving of 1 mol of solute, ΔsolH)
(ii)
explanation and use of the term enthalpy change of hydration (dissolving of 1 mol of gaseous ions in water, ΔhydH)
5.2.1(d)
(i)
use of the enthalpy change of solution of a simple ionic solid (e.g. NaCl, MgCl₂) and relevant energy terms (enthalpy change of hydration and lattice enthalpy) for the construction of enthalpy cycles
(ii)
use of the enthalpy change of solution of a simple ionic solid (e.g. NaCl, MgCl₂) and relevant energy terms (enthalpy change of hydration and lattice enthalpy) for related calculations
5.2.1(e)
i
qualitative explanation of the effect of ionic charge on the exothermic value of a lattice enthalpy
ii
qualitative explanation of the effect of ionic radius on the exothermic value of a lattice enthalpy
iii
qualitative explanation of the effect of ionic charge on the exothermic value of an enthalpy change of hydration
iv
qualitative explanation of the effect of ionic radius on the exothermic value of an enthalpy change of hydration