Some solids, such as anhydrous Na 2 SO 4 , and many liquids and gases dissolve by
exothermic processes. Their solubilities usually decrease as temperature increases. The
solubility of O 2 in water decreases (by 34%) from 0.041 gram per liter of water at 25°C
to 0.027 gram per liter at 50°C. Raising the temperature of rivers and lakes by dumping
heated waste water from industrial plants and nuclear power plants is called thermal pollu-
tion.A slight increase in the temperature of the water causes a small but significant
decrease in the concentration of dissolved oxygen. As a result, the water can no longer
support the marine life it ordinarily could.
The dissolution of anhydrous
calcium chloride, CaCl 2 , in water is
quite exothermic. This dissolution
process is utilized in commercial
instant hot packs for quick treatment
of injuries requiring heat.14-6 Effect of Temperature on Solubility 553Calcium acetate, Ca(CH 3 COO) 2 , is more soluble in
cold water than in hot water. When a cold,
concentrated solution of calcium acetate is heated,
solid calcium acetate precipitates.See the Saunders Interactive
General Chemistry CD-ROM,
Screen 14.5, Factors Affecting Solubility
(1): Henry’s Law and Gas Pressure.