The solubility of nonpolar gases decreases with temperature to a minimum

Scientific Explanation

In most solvents, gas solubility decreases monotonically with rising temperature. Water behaves differently: the solubility of nonpolar gases like oxygen, nitrogen, or methane first decreases, passes through a minimum (typically between 80 and 100 degrees Celsius), and then increases again at even higher temperatures.

This behavior is explained by the hydrophobic effect. At low temperatures, water molecules form clathrate-like cage structures around nonpolar gas molecules — ordered cages of hydrogen bonds that enclose the gas molecule. Forming these cages is entropically unfavorable but enthalpically favorable. Upon warming, the cage structures become unstable, and solubility drops.

At still higher temperatures, however, the nature of the dissolution process changes fundamentally. Hydrogen bonds are increasingly disrupted, water becomes “more normal,” and accommodating gas molecules becomes easier again. Near the critical point, water and gas become almost freely miscible.

Everyday Relevance

This solubility minimum explains several everyday observations. Cold water can dissolve more oxygen than warm water — this is why a cold mountain stream contains more dissolved oxygen than a warm pond, which is vital for fish and other aquatic organisms. Warming of water bodies through climate change or power plant cooling water reduces oxygen content and threatens aquatic ecosystems.

Opening a warm carbonated drink releases more fizz than opening a cold one — the lower gas solubility at higher temperature is directly noticeable.