The effect that an increase in temperature will have on the solubility of a solid is to increase its solubility if the reaction between the solute and the solvent is endothermic. If the reaction between the solute and solvent is exothermic, however, an increase in temperature will decrease the solubility of the solid. Endothermic reactions absorb heat and exothermic reactions give off heat.
In an endothermic reaction, the stored heat energy is on the reactant, or left-hand, side of the reaction equation along with the solid, or solute. Adding heat introduces stress, and as predicted by Le Chatelier's principle, the reaction is pushed to the product, or right-hand, side of the reaction equation. The solute and solvent are attempting to achieve equilibrium and alleviate the induced heat stress by dissolving the solute.
An exothermic reaction represents the inverse of the prediction; the stored heat energy is on the product, or right hand, side of the reaction equation. Increasing the temperature adds stress to the product side, and the solubility of the solid on the reactant, or left-hand, side is decreased to relieve the heat-induced stress on the product side.