Topic B. Factors Affecting Solubility
Le Châtelier's principle governs
the response of a system in equilibrium when a stress is introduced. Some “stressors”
that affect solubility equilibria are presence of common ion, pH
and presence of a complexing agent.
Subtopic B.2. Effect of Temperature on Solubility of Solids
Le Châtelier's principle governs the response of a system in equilibrium when a stress is introduced. Some “stressors” that affect solubility equilibria are presence of common ion, pH and presence of a complexing agent.
Effect of temperature in solubility values has been determined for solid solutes in liquid solvents. These effects differ depending on whether the reaction is endothermic or exothermic. Using Le Châtelier's principle, the effects of temperature in both scenarios can be determined.
1. First, consider an endothermic reaction (ΔHsolvation > 0): Increasing the temperature results in a stress on the reactants’ side from the additional heat. Le Châtelier’s principle predicts that the system shifts toward the product side in order to alleviate this stress. By shifting towards the product side, more of the solid is dissociated when equilibrium is again established, resulting in increased solubility.
2. Second,
consider an exothermic reaction (ΔHsolvation<0): Increasing
the temperature results in a stress on the products’ side from the additional
heat. Le Châtelier’s principle predicts that the system shifts
toward the reactant side in order to alleviate this stress. By
shifting towards the reactant's side, less of the solid is dissociated when
equilibrium is again established, resulting in decreased solubility.
(Text excerpt adapted from Solubility and Factors Affecting Solubility by Tran and Liu, 2020)