Chem- periodicity and ionic bonds

Question

1. Consider an ionic compound, MX2, composed of generic metal M and generic, gaseous halogen X.The enthalpy of formation of MX2 is Δ𝐻∘f=−987 kJ/mol.
2. The enthalpy of sublimation of M is Δ𝐻sub=125 kJ/mol.
3. The first and second ionization energies of M are IE1=677 kJ/mol and IE2=1.390×103 kJ/mol.
4. The electron affinity of X is Δ𝐻EA=−351 kJ/mol. (Refer to the hint.)
5. The bond energy of X2 is BE=201 kJ/mol.

Determine the lattice energy of MX2.

Δ𝐻lattice=

Answer 1

This question is about the Born Haber cycle. If not familiar, please investigate it.

M(s) + X₂(g) ==> MX₂ ∆H_f = -987 kJ/mol

M(s) => M(g) ∆H_sub = 125 kJ/mol

M(g) => M⁺(g) IE1 = 677 kJ/mol

M⁺(g) => M²⁺(g) IE2 = 1390 kJ/mol

X₂(g) => 2X(g) BE = 201 kJ/mol

2X(g) => 2X^-(g) EA = -351 kJ/mol x 2 = -752 kJ

∆H_f = ∆H_sub + IE + BE + EA + LE

Solve for LE (lattice energy):

-987 = 125 + 677 + 1390 + 201 -752 + LE

LE = -2628 kJ/mol