1. For an ionic compound the lattice enthalpy is the heat
energy released when one mole of solid in its standard state
is formed from its ions in the gaseous state.
This value cannot be determined directly and so we make
use of changes for which data are available and link them
together with an enthalpy cycle.
This enthalpy cycle is based on the formation of the compound
from its elements in their standard states.

2. BORN-HABER CYCLE
FOR
SODIUM CHLORIDE

3. kJ H= +107kJmol-1 Atomisation of sodium +800 +700 +600 +500 +400 +300
+200
Na(g) + 1/2 Cl2(g)
+100
H= +107kJmol-1
Na(s) + 1/2 Cl2(g)
-400
-300
-200
-100
Atomisation of sodium

4. kJ H = +121kJmol-1 Atomisation of chlorine +800 +700 +600 +500 +400
+300
Na(g) + Cl(g)
+200
H = +121kJmol-1
Na(g) + 1/2 Cl2(g)
+100
Na(s) + 1/2 Cl2(g)
-400
-300
-200
-100
Atomisation of chlorine

5. kJ e- e- e- e- e- e- e- e- e- e- e- + H = +502kJmol-1
+800
Na+(g) + Cl(g)
+700 e- e- e- e-
+600 e- e-
+500 e- e-
+400 e-
H = +502kJmol-1 e- e-
+300
Na(g) + Cl(g)
+200 +
Na(g) + 1/2 Cl2(g)
+100
Na(s) + 1/2 Cl2(g)
-400
-300
-200
-100
First Ionisation of sodium

6. First electron affinity of chlorinekJ kJ kJ
+800
+800
+800
Na+(g) + Cl(g)
+700
+700
+700
+600
+600
+600
H = -355kJmol-1
+500
+500
+500
+400
+400
+400
Na+(g) + Cl-(g)
+300
+300
+300
Na(g) + Cl(g)
Na(g) + Cl(g)
Na(g) + Cl(g)
+200
+200
+200 - e-
Na(g) + 1/2 Cl2(g)
Na(g) + 1/2 Cl2(g)
Na(g) + 1/2 Cl2(g)
+100
+100
+100
Na(s) + 1/2 Cl2(g)
Na(s) + 1/2 Cl2(g)
Na(s) + 1/2 Cl2(g)
-400
-300
-200
-100
-400
-300
-200
-100
-400
-300
-200
-100
First electron affinity of chlorine

7. kJ kJ kJ - + H = -411kJmol-1 +800 +800 +800 +700 +700 +700 +600 +600
Na+(g) + Cl(g)
+700
+700
+700
+600
+600
+600
+500
+500
+500
+400
+400
+400
Na+(g) + Cl-(g)
+300
+300
+300 - +
Na(g) + Cl(g)
Na(g) + Cl(g)
Na(g) + Cl(g)
+200
+200
+200
Na(g) + 1/2 Cl2(g)
Na(g) + 1/2 Cl2(g)
Na(g) + 1/2 Cl2(g)
+100
+100
+100
Na(s) + 1/2 Cl2(g)
Na(s) + 1/2 Cl2(g)
Na(s) + 1/2 Cl2(g)
-400
-300
-200
-100
-400
-300
-200
-100
-400
-300
-200
-100
H = -411kJmol-1
Formation of sodium chloride
NaCl(s)

8. kJ kJ kJ - - - - - + + + + H = -786 kJmol-1 +800 +800 +800 +700 +700
Na+(g) + Cl(g)
+700
+700
+700
+600
+600
+600
+500
+500
+500
+400
+400
+400
Na+(g) + Cl-(g)
+300
+300
+300
Na(g) + Cl(g)
Na(g) + Cl(g)
Na(g) + Cl(g)
+200
+200
+200 - -
Na(g) + 1/2 Cl2(g)
Na(g) + 1/2 Cl2(g)
Na(g) + 1/2 Cl2(g) +
+100
+100
+100 + - +
Na(s) + 1/2 Cl2(g)
Na(s) + 1/2 Cl2(g)
Na(s) + 1/2 Cl2(g) - + -
-400
-300
-200
-100
-400
-300
-200
-100
-400
-300
-200
-100
H = -786 kJmol-1
Lattice enthalpy for sodium chloride
NaCl(s)