• ΔH enthalpy abbreviations used for the Born-Haber Cycle of potassium bromide

  • f = enthalpy of formation

  • atom = atomisation energy

  • IE = ionisation energy

  • LE = lattice enthalpy expressed exothermically i.e. from free gaseous ions to ionic crystals.

  • elec.affin = electron affinity

• Each cycle involves 6–8 enthalpy values, of which you must know all of them except one!

• You can then calculate the unknown enthalpy value by substitution and simple algebraic rearrangement.

• No numerical values are shown on all Born–Haber cycle diagrams, but some are shown on selected enthalpy level diagrams.

K(s)	+	1/2Br2(l)	ΔHθf(KBr)	K+Br–(s)
ΔHθatom(K)		ΔHθatom(Br2)			ΔHθLE(KBr)
		Br(g) +  e-	ΔHelec. affin.(I)	Br–(g) +
K(g)	ΔHθ1st IE(K)				K+(g) +  e-
The Born–Haber Cycle for the formation of a potassium bromide, an ionic halide salt

From Hess's Law

ΔH^θ_f(KBr) = ΔH^θ_atom(K) + ΔH^θ_atom(Br₂) + ΔH^θ_{1st IE}(K) + ΔH^θ_elec.affin.(Br)  + ΔH^θ_LE(KBr)

rearranging gives the lattice enthalpy of potassium bromide and be very careful of the signs in the algebra as well as the enthalpy values!

- ΔH^θ_LE(KBr) = ΔH^θ_atom(K) + ΔH^θ_atom(Br₂) + ΔH^θ_{1st IE}(K) + ΔH^θ_elec.affin.(Br)  - ΔH^θ_f(KBr)

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Other lattice enthalpies that can be calculated with the potassium bromide general Born-Haber Cycle expressed as an enthalpy level diagram

A general Born-Haber Cycle for a group 1 metal halide salt using an enthalpy level diagram.

ΔH_f^θ(MX) = standard enthalpy of formation of group 1 halide salt e.g. bromide  (↓ exothermic)

ΔH^θ_at(M) = standard enthalpy of atomisation of the group 1 metal (↑ endothermic)

 ΔH^θ_atom(X₂) = standard enthalpy of atomisation of the halogen e.g. bromine (↑ endothermic, watch the state)

 ΔH^θ_ea.(X) = standard enthalpy of the electron affinity of the halogen e.g. bromine (↓ exothermic)

ΔH^θ_{1st IE}(M) = standard enthalpy of the 1st ionisation of the group 1 metal (↑ endothermic)

ΔH^θ_LE(MX) = lattice enthalpy of the halide salt e.g. bromide (↑ endothermic)

From Hess's Law: route B = route A

ΔH_f^θ(MX) + ΔH^θ_LE(MX) = ΔH^θ_at(M) + ΔH^θ_atom(X) + ΔH^θ_{1st IE}(M) +  ΔH^θ_ea.(X)

rearranging to get the lattice enthalpy of any group 1 metal halide and be very careful of the signs in the algebra as well as the enthalpy values!

ΔH^θ_LE(MX) = ΔH^θ_at(M) + ΔH^θ_atom(X) + ΔH^θ_{1st IE}(M) +  ΔH^θ_ea.(X) - ΔH_f^θ(MX)

So you can solve for any unknown e.g. lattice enthalpy of potassium bromide and watch the signs.

The full enthalpy level diagram for the Born-Haber Cycle for any group 1 halide salt, assumed to be a pure ionic compound. Key below the diagram.

Using Br₂(l), all the bromides from group I metals, lithium bromide LiBr, sodium bromide NaBr, potassium bromide KBr, rubidium bromide RbBr, caesium bromide CsBr and francium bromide FrBr.

Hence you can calculate the lattice enthalpy of any group 1 metal halide assuming it is a purely ionic compound.

See also the Born-Haber Cycle for Group 1 bromides and Group 1 iodides

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Born-Haber Cycle and Lattice Enthalpy INDEX

Energetics–Thermochemistry–Thermodynamics Notes INDEX

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How to draw the Born-Haber Cycle for potassium bromide, how to calculate the lattice enthalpy for potassium bromide from a Born-Haber Cycle, a full explanation of the terms and enthalpy values of the Born-Haber Cycle for potassium bromide, what do I need to know about the Born-Haber Cycle of potassium bromide for AQA, Edexcel, OCR, Salters, CIE, WJEC Eduqas & CCEA  A-level chemistry, US grades 11-12 K12 AP Honors chemistry courses, how to use enthalpies of formation, ionisation, atomisation, electron affinity and lattice enthalpy to problem solve the Born-Haber Cycle for potassium bromide.