Construct a Born-Haber cycle and use it to calculate the first electron affinity of chlorine.

Question

ΔH_atm(Cl) = +122 kJ/mol

ΔH_atm(Mg) = +148 KJ/mol

ΔH_{1st ionisation energy(Mg)} = +738 kJ/mol

ΔH_{2nd ionisation energy(Mg)} = +1451 kJ/mol

ΔH_{lattice energy(MgCl2)} = -2526 kJ/mol

ΔH_{formation(MgCl2)} = -641 kJ/mol

Answer 1

I'm uncertain as to what ∆H_atm refers to but will assume it is sublimation and binding energy.

Setting up the Born-Haber cycle for MgCl₂, we would have something like the following:

Mg(s) + Cl₂(g) ===> MgCl₂(s) ... ∆Hf = -641 kJ/mol

M(s) ==> Mg(g) .. ∆Hsub = 148 kJ/mol

M(g) ==> Mg⁺(g) .. IE1 = 738 kJ/mol

Mg⁺(g) ==> Mg⁺⁺(g) .. IE2 = 1451 kJ/mol

Cl₂(g) ==> 2Cl(g) .. BE = 122 kJ/mol

2Cl(g) ==> 2Cl^-(g) .. EA1 + EA2

Mg(g)²⁺ + 2Cl^-(g) ==> MgCl₂(s) .. LE = -2526 kJ/mol

∆Hf = ∆Hsub + IE + BE + EA + LE

-641 = 148 + 738 + 1451 + 122 + EA - 2526

EA = -708 kJ/mol (total for EA1 + EA2)

EA1 = -354 kJ/mol

(be sure to check all of the math)