27.1.2—Trends: the variation in solubility

Dissolution is favoured when hydration enthalpy gained offsets lattice energy required. Group 2 hydroxide and sulfate trends differ because lattice and hydration terms change at different rates down the group.

Use the energy balance and the measured solubility together; a more exothermic solution enthalpy does not automatically mean greater solubility because entropy also contributes.

Hydroxide solubility generally rises down Group 2 while sulfate solubility falls, showing that one simple “larger ion” rule cannot explain both salts.

Do not equate ΔHsol directly with solubility or ignore the opposing lattice/hydration terms.