1. Born-Haber Cycles ΔHat (Na(s)) 109 kJ mol-1 Bond dissociation (Cl2(g))
The Born-Haber cycle is an enthalpy level diagram breaking down the formation of an ionic compound using simpler steps.
The Born-Haber cycle can be used to find an unknown enthalpy value by applying Hess’s law
Example: Calculate ΔHꝋlatt for Na+(g) + Cl-(g)
ΔHat (Na(s))
109 kJ mol-1
Bond dissociation (Cl2(g))
121 kJ mol-1
First ionisation energy (Na)
494 kJ mol-1
First electron affinity (Cl)
-364 kJ mol-1
ΔHf (NaCl(s))
-411 kJ mol-1

2. Na+(g) + e- + Cl(g) enthalpy Na+(g) + e- + ½Cl2(g) Na+(g) + Cl-(g)
Bond Dissociation(Cl2)
1st Electron Affinity (Cl)
enthalpy
Indirect route
Na+(g) + e- + ½Cl2(g)
Na+(g) + Cl-(g)
1st Ionisation (Na)
Na(g) + ½Cl2(g)
∆Hlatt
∆Hat (Na)
Direct Route
Na(s) + ½Cl2(g)
∆Hf
NaCl(s)

3. First ionisation energy (Mg) 736 kJ mol-1
Draw a Born-Haber cycle for magnesium oxide and use it to calculate the 2nd electron affinity of O
ΔHat (Mg(s))
150 kJ mol-1
ΔHat (O2(g))
248 kJ mol-1
First ionisation energy (Mg)
736 kJ mol-1
Second ionisation energy (Mg)
1450 kJ mol-1
First electron affinity (O)
-142 kJ mol-1
ΔHf (MgO(s))
-602 kJ mol-1
ΔHꝋlatt (MgO(g))
3889 kJ mol-1

4. Mg2+(g) + 2e- + O(g) Mg2+(g) + O2-(g) enthalpy Mg2+(g) + 2e- + ½O2(g)
Bond Dissociation(O2)
Mg2+(g) + O2-(g)
1st Electron Affinity (O)
2dn Electron Affinity (O)
Mg2+(g) + 2e- + ½O2(g)
Mg2+(g) + O-(g)
2nd ionisation (Mg)
Mg+(g) + e- + ½O2(g)
1st ionisation (Mg)
Mg(g) + ½O2(g)
∆Hlatt
∆Hat (Mg)
Mg(s) + ½O2(g)
∆Hf
MgO(s)

5. First ionisation energy (Ca) 590 kJ mol-1
Using the values given in the table below, construct a Born-Haber cycle and calculate the ΔHꝋlatt for CaF2
ΔHat (Ca(s))
179 kJ mol-1
ΔHat (F2(g))
158 kJ mol-1
First ionisation energy (Ca)
590 kJ mol-1
Second ionisation energy (Ca)
1150 kJ mol-1
First electron affinity (F)
-348 kJ mol-1
ΔHf (CaF2(s))
-1220 kJ mol-1

6. Ca2+(g) + 2e- + 2F(g) enthalpy Ca2+(g) + 2e- + F2(g) Ca2+(g) + 2F-(g)
Bond Dissociation
1st Electron Affinity
Ca2+(g) + 2e- + F2(g)
Ca2+(g) + 2F-(g)
2nd ionisation
Ca+(g) + e- + F2(g)
1st ionisation
Ca(g) + F2(g)
∆Hlatt
∆Hat
Ca(s) + F2(g)
∆Hf
CaF2(s)