Born-Haber Cycles

enthalpy H

eg for sodium chloride:

NaCl (s)

Na+ (g) + Cl- (g)

H lattice

associationNa (s) + ½ Cl2 (g)

H formation

H atomisation

Na (g) + ½ Cl2 (g)

H atomisation

Na (g) + Cl (g)

Na+(g)+ Cl(g) + e-

H first ionisation energy H first electron affinity

Born-Haber CyclesThere are two routes from

enthalpy H

NaCl (s)

Na+ (g) + Cl- (g)

H lattice

associationNa (s) + ½ Cl2 (g)

H formation

H atomisation

Na (g) + ½ Cl2 (g)

H atomisation

Na (g) + Cl (g)

Na+ (g) + Cl (g)

H first ionisation energy H first electron affinity

elements to ionic compound

HatmNa + HatmCl + H1st IE + H1st EA + Hlattice = Hformation

Apply Hess’s Law:

: applying Hess’s Law

Born-Haber Cycles: applying Hess’s Law

HatmNa + HatmCl + H1st IE + H1st EA + Hlattice = Hformation

Rearrange to find the lattice energy:

Hlattice = Hformation - (HatmNa + HatmCl + H1st IE + H1st EA)

So Born-Haber cycles can be used to calculate a measure of ionic bond strength based on experimental data.