The solubilties of most ionic solids increase as the temperature increases.
Dissolving of a solid in water is, in most cases, an endothermic reaction. In dissolving, as in melting, a solid becomes a liquid. It takes more energy to be a liquid than to be a solid at the same temperature. When the solution becomes saturated at any temperature, a dynamic equilibrium is established between the dissolved and undissolved solid. When heat is added that results in a higher temperature, the extra heat favors the endothermic reaction, and more solid dissolves rather than crystallizes until new equilibrium system is established again. Hence, at a higher temperature, more solid is dissolved in water. This increases the solid's solubility.
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