How Does Temperature Affect the Solubility of Gases in Water?

Colder Water Holds More Gas

• All gases follow the pattern that they are more soluble in colder water. For example, 1 kg of water can hold up to 0.03 g of nitrogen gas at 0 degrees Celsius (assuming one atmosphere of pressure). However, at 60 degrees Celsius the maximum amount of suspended nitrogen drops to 0.01 g. Other gases, like helium, however, may be less soluble. In a kilogram of water, only 0.0017 g of helium can be suspended in water at 0 degrees Celsius, and at 60 degrees Celsius this drops down to 0.0013 g.

Why Colder Water Holds More Gas

• The reason why lower temperatures are necessary for gas solubility is that temperature is a measurement of entropy, or disorder caused by the kinetic energy of the liquid and gas molecules. With low entropy, gases can form weak molecular bonds with the water molecules. As the temperature increases, these bonds are too weak to overcome the motion of the molecules. As a result, when temperature increases the gas molecules raise to the surface and escape into the atmosphere.

Examples of Gas Solubility

• It's easy to visualize the relationship between gas solubility and water temperature by relating it to real-world applications. A common example is the difference in taste in soft drinks at different temperatures. When soda becomes warm, it holds less carbon dioxide, causing the soda to fizz and taste flat. Another example is that fish adapt to certain temperature ranges because warm water holds less oxygen. If a body of water suddenly increases in temperature, it can cause fish to die because there is less oxygen for them to breathe.

Solid Solvents and Water Temperature

• One cause of confusion regarding how temperature affects solubility is that the rule is reversed for solid solvents in water. As water temperature increases, the solubility of solid matter increases. This is because the increased entropy breaks apart the molecular bonds that hold solid matter together, causing it to dissolve into a solution. This is why it's easier to dissolve a cup of sugar in hot water than cold water.