Solubility And Temperature Dependence

Question

For a solid solute dissolving in a liquid solvent, which of the following statements correctly describes the effect of temperature on solubility, and which thermodynamic condition supports it?

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The dissolution of a solid in a liquid can be treated as an equilibrium: solute (solid) ⇌ solute (solution), with an associated enthalpy change. Le Chatelier's principle states that increasing temperature shifts an equilibrium in the endothermic direction. Therefore, if dissolution is endothermic (ΔH_sol > 0), increasing temperature increases solubility. If dissolution is exothermic (ΔH_sol < 0), as in the case of anhydrous CaCl₂ or Na₂SO₄ (above a certain temperature), increasing temperature decreases solubility. Option A is incorrect because dissolution of some salts like Ca(OH)₂ and Li₂SO₄ is exothermic, and their solubility decreases with temperature. Option C is not a thermodynamic rule — ionic compounds can show either positive or negative temperature dependence. Option D incorrectly generalises; entropy upon dissolution is generally positive (increase in disorder), and it does not alone determine the temperature dependence. The concept is rooted in the NCERT unit on equilibrium and the thermodynamics of dissolution. Plausibility check: NaCl shows slight increase and Ce₂(SO₄)₃ shows a decrease — both are consistent with the correct answer.

Solubility And Temperature Dependence

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