Henry’s Law (Gas Solubility)

Governs how much oxygen (or any gas) dissolves in water. Higher partial pressure of the gas drives more into solution; solubility falls as temperature rises. Explains why roughly 21 percent atmospheric oxygen sets the dissolved oxygen level in water exposed to air.

$$C=k_{H}P$$

Variables

Symbol	Meaning	Unit
C	dissolved gas concentration in water	mg/L
$k_H$	Henry’s Law solubility coefficient (temperature dependent, falls as temperature rises)	mg/(L·atm)
P	partial pressure of the gas above the water	atm

Worked example

Water exposed to air at room temperature, with oxygen at about 21 percent of atmospheric pressure, holds roughly 8 mg/L dissolved oxygen.

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Part of The Blueprint of Water