Consider the following information. Determine the enthalpy of formation, Δ𝐻f, for CsCl(s).

Question

1. The lattice energy of CsCl is Δ𝐻lattice=−657 kJ/mol.
2. The enthalpy of sublimation of Cs is Δ𝐻sub=76.5 kJ/mol.
3. The first ionization energy of Cs is IE1=376 kJ/mol.
4. The electron affinity of Cl is Δ𝐻EA=−349 kJ/mol.
5. The bond energy of Cl2 is  BE=243 kJ/mol.

Answer 1

Refer to the Born Haber cycle (as shown in my previous answer). So without going through all the steps ..

∆Hf = ∆Hsub + IE + 1/2BE + EA + LE

∆Hf = 76.5 + 376 + (1/2 x 243) + (-349) + (-657)

∆Hf = 76.5 + 376 + 121.5 - 349 - 657

∆Hf = -432 kJ/mol