The solubility of gases in a solvent is not fixed and it changes as the temperature of the solvent changes. For water, the solubility of the gases decreases as the temperature rises. Consequently, the solubility of gases in water increases as the temperature decreases. This is one of the reasons why environmental scientists are worried about the discharge of hot or warm wastewater in our rivers. This causes an increase in water temperature, which reduces the dissolved oxygen levels and makes life difficult for fishes, etc. Organic solvents exhibit an opposite trend, with an increase in solubility as the temperature increases. The solubility of gases in solvents can be understood by using Le Chatelier's Principles, according to which the equilibrium shifts in a direction so as to have least stress. In case of water, addition of oxygen causes heat release and this stress can be relieved by decreasing the solubility so as to counter the addition of heat (by temperature increase). In case of organic solvents, heat is consumed when gases are dissolved and thus, temperature increase favors solubility increase, so as to have least stress.
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