Born Haber’s cycle method:
Mg(s) + Br2(l) → MgBr ∆Hf°
Sublimation: Mg(g) → Mg2+(g) ∆H1°
Ionisation: Mg(g) → Mg2+(g) + 2e ∆H2°
Vapourisation: Br2(l) → Br2(g)∆H3°
Dissociation: Br2(g) → 2Br(g) ∆H4°∆H4°
Electron affinity: 2Br(g) + 2e- → 2Br- ∆H5°
Lattice enthalpy: Mg2+(g) + 2Br-(g) → MgBr2(s) ∆H6° = ?
∆Hf ° = ∆H1 ° + ∆H1° + ∆H2° + ∆H3° + ∆H4° + ∆H5° + ∆H6°
∆H6° = ∆Hf° – (∆H1° + ∆H1 ° + ∆H2° + ∆H3° + ∆H4° + ∆H5°)
If we know the values of ∆Hf° , ∆H1° , ∆H2° , ∆H3° , ∆H4° and ∆H5° , we can calculate the value of ∆H6° by indirect method.
