Henry's Law
The solubility of a gas in a liquid is directly proportional to the partial pressure of that gas above the liquid.
Formula / equation
p = K_H × x
Unit
Pa
In depth
The law holds for gases that do not react with the solvent and at moderate pressures. Since the Henry constant rises with temperature, gases become less soluble as the liquid warms, which is why boiling drives dissolved air out of water and why warming rivers hold less oxygen.
Examples in the real world
CO₂ fizzing out when a bottle is opened and the pressure drops; nitrogen dissolving in a diver's blood at depth.