Question

In an ionic compound, the size of the ions affects the internuclear distance (the distance between the centers of adjacent ions), which affects lattice energy (a measure of the force need to pull ions apart), which affects the enthalpy of solution. Based on ion sizes, rank these compounds by their expected heats of solution. Most exothermic to most endothermic. Substances are Kf Kl KBr KCl

Answer 1

Hello

As you have the same cation in these salts, only the anion has to be compared. Note that the charge density of anion decreases from fluoride to iodide. Since fluoride has the highest charge density because of its smallest radius in the halogen family, potassium fluoride would have the highest lattice enthalpy. The trend for lattic enthalpy is:
KF>KCl>KBr>KI

Since you require most energy to split KF it will be most endothermic. the trend will be:

KF<KCl<KBr<KI this is the trend of endothermicity based on lattice energy. KF is most endothermic and KI being most exothermic.