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Born-Haber Cycles (A2 Only)

Chemistry: AQA A Level, topic 2.1.1

Enthalpy Changes

The different types of enthalpy changes are:

Lattice enthalpy

Lattice enthalpy

  • Lattice enthalpy can be defined in two different ways:
  • Formation - Lattice enthalpy is the enthalpy change when one mole of perfect crystal is formed from its gaseous ions.
  • Dissociation - Lattice enthalpy is the enthalpy change when one mole of crystal dissociates into its gaseous ions.
Enthalpy of formation

Enthalpy of formation

  • The enthalpy of formation is the enthalpy change when one mole of a substance is produced from its elements in their standard states.
Ionisation energy

Ionisation energy

  • The ionisation energy is the energy change when one mole of gaseous atoms loses one mole of electrons to form one mole of gaseous ions.
Enthalpy of atomisation

Enthalpy of atomisation

  • The enthalpy of atomisation is the enthalpy change when one mole of gaseous atoms is formed from the element in its standard state.
Bond enthalpy

Bond enthalpy

  • The bond enthalpy is the average enthalpy change on formation of a mole of identical bonds in the gas phase.
Electron affinity

Electron affinity

  • The electron affinity is the enthalpy change when one mole of electrons is added to one mole of gaseous atoms to form one mole of gaseous ions.

Born-Haber cycles

A Born-Haber cycle can be used to calculate some of the types of enthalpy changes from experimental data.

Born-Haber cycles

Born-Haber cycles

  • You can break down an ionic reaction into a series of steps.
  • You turn the pure elements into gaseous atoms.
  • Then you form the ions.
  • Via electron ionisation and affinity.
  • Then you condense the gaseous ions into a crystal.
  • You can use this principle to generate a Born-Haber cycle.
  • An example is on the next slide.
Example Born-Haber cycle

Example Born-Haber cycle

Test yourself on Born-Haber Cycles (A2 Only)

  • Which of these is the correct definition for ionisation energy?

  • The process of an element accepting an electron to form the negative ion is called which if the following?

  • The ions formed from the compound MgCl2 are which of the following?

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