Lattice energy U(MX2) to calculate
Use Born-Haber(-Fajans) Cycle
for more info: wikipedia
M(s) + X2 → MX2(s) ΔHf°MX2 = -957 kJ mol^-1
M(s) →ΔHsub(M)→ M(g) ΔHsub = 123kJ mol^-1
M(g) →ΔHIE1(M)→ M^+ + e⁻ 757 kJ mol^-1
M^+→ΔHIE2(M)→ M^2+ + e⁻ 1451 kJ mol^-1
X2 →ΔHBE(X2)→ 2X +153 kJ mol^-1
X + e⁻→ΔHEA(X)→ X^- -313 kJ mol^-1
ΔHfo = U + ΔHsub(M) + IE1 + IE2 + ΔHdissX2 + 2EA1(X)
-957= U + 123 + 757 + 1451 + 153 – 626 = U + 1858
U = -2815 kJ mol^-1 The –ve sign is often dropped
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