Question

How do you determine what ionic substance has more exothermic lattice energy?

for example if you compare NaCl and KCl???

Answer 1

The charge difference between cation and anion as well as the size of the ion usually controls the lattice energy. Since the anion is the same (Cl^-) and the charges are the same (+1 on cation and -1 on anion), then the size probably makes the difference. Na ion is smaller than the K ion; therefore, we would expect NaCl to have the larger lattice energy because it forms the more compact crystal.