Both sodium chloride and potassium chloride readily dissolve in water at room temperature, even though the lattice energy of NaCl is significantly larger in magnitude than that of KCl.
Consider how differences in ionic size influence the various energetic contributions to dissolution and the resulting free-energy change.
(a) Qualitatively compare the lattice energies of NaCl and KCl and explain how cation size affects lattice energy.
(b) Discuss how cation size influences the magnitude of the hydration enthalpy for Na⁺ versus K⁺ and how this offsets the difference in lattice energy.
(c) Explain why the entropy change upon dissolution helps to make both salts thermodynamically favorable, and account for the fact that their solubilities at 25 °C are of the same order of magnitude despite the energetic differences described in parts (a) and (b).