The lattice enthalpies of NaCl, KCl and AgCl are - 787, - 717 and - 916 kJ mo1^-1, respectively. Based on these values, arrange them in increasing order of water solubility and justify your answer.
AgCl < KCl < NaCl
For highly ionic compound lattice energy is directly proportional to water solubility.
Technically the lattice energy in KCl is lower because of the larger size of the potassium ion. This increase in size means that the oppositely charged ions in KCl are further part than those in NaCl and therefore it takes less energy to break up the ionic bond in KCl which we see as a reduction in the water solubility. The cation Ag is large in size, so its salt is almost insoluble in water.