We cannot measure the second electron affinity of oxygen directly: O- (g) + e -

Question

We cannot measure the second electron affinity of oxygen directly:
O- (g) + e - ----> O2- (g) EA2=?
The oxygen ion can exist in the solid state, but where the high energy requirement for its formation is offset by the large lattice energies of ionic oxides.
(a) Show that EA2 can be calculated from the enthalpy of formation and lattice energy of MgO(s), enthalpy of sublimation of Mg (s), bond energy of O2 and EA for O (g).
(b) The lattice energy of MgO is -3925 kJ/mol. Combine this with other values in the text to estimate EA2 for oxygen. Include Born Haber Cycle DDiagram

Explanation / Answer

delta Evap = 147.1 kj/mol -2.48 kj/mol = 144.6 kj/mol deltaE reaction = delta E vap + IE1+IE2+1/2BE + EA1 + EA2 -LE EA2 = delta Ereaction = deltaEvap - IE1-IE2-1/2BE-EA1 + LE EA2 = [-602-145-738-1451-248-(-141)+3925 kj/mol EA2 = 882 kj/mol

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