Chapter 8, Problem 121RQ

Changing $\text{1 mol of Mg}\left(s\right)\text{ and }\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.{\text{ mol of O}}_{\text{2}}\left(g\right)$ to gaseous atoms requires a total of approximately 150 kJ of energy. The first and second ionization energies of magnesium are 737 and 1450 kJ/mol, respectively; the first and second electron affinities of oxygen are $\text{—141 and +844 kJ/mol}$, respectively; and the standard heat of formation of $\text{MgO}\left(s\right)\text{ is —602 kJ/mol}$. Construct an enthalpy diagram similar to the one in Figure 8.4 and use it to calculate the lattice energy of magnesium oxide. How does the lattice energy of MgO compare with that of NaCl? What might account for the difference?