The molar lattice energies (U) and hydration enthalpies (ΔH_hyd) for three chloride salts at 25 °C are listed below:
Salt U (kJ mol⁻¹) ΔH_hyd (kJ mol⁻¹)
NaCl +787 −783
KCl +715 −690
AgCl +905 −846
Assume that the enthalpy of solution (ΔH_soln) for each salt can be approximated by
ΔH_soln ≈ ΔH_hyd + U.
Entropy contributions are comparable and need not be calculated.
(a) Calculate ΔH_soln for each salt, reporting values to the nearest kilojoule per mole.
(b) Using the calculated enthalpies, predict the order of aqueous solubility of the three salts at 25 °C (most soluble to least soluble).
(c) Explain how the relative magnitudes of lattice energy and hydration enthalpy combine to influence the observed solubility trend.