Consider the following information. Determine the second electron affinity of O.

Question

1. The enthalpy of formation of CaO is Δ𝐻∘f=−634.9 kJ/mol.
2. The enthalpy of sublimation of Ca is Δ𝐻sub=177.8 kJ/mol.
3. The first and second ionization energies of Ca are IE1=590 kJ/mol and IE2=1145 kJ/mol.
4. The first electron affinity of O is Δ𝐻EA1=−142 kJ/mol.
5. The bond energy of O2 is  BE=498 kJ/mol.
6. The lattice energy of CaO is Δ𝐻lattice=−3414 kJ/mol.

Answer 1

Refer to the Born Haber cycle for CaO

Ca(s) + 1/2 O₂(g) ==> CaO

∆H_f = ∆H_sub + IE1 + IE2 + 1/2 BE + EA1 + EA2 + LE

-634.9 = 177.8 + 590 + 1145 + (1/2 x 498) + (-142) + EA2 + (- 3414)

-634.9 = -1394.2 + EA2

EA2 = +759 kJ/mol

(be sure to check the math. also note that EA2 is positive since it is endothermic whereas EA1 is negative indicating it is exothermic)