Henry's Law describes the relationship between the pressure of a gas above a liquid and the amount of the gas that will dissolve in the liquid.
|:||Concentration (moles per volume)|
|:||Mole Fraction in Liquid|
Henry's law tells us that the amount of gas that will dissolve in a liquid is proportional to the pressure of the gas. Unfortunately Henry's Law may be defined in a number of ways, and the constant used must be selected to match the particular formulation of the law.
Formulations of Henry's Law
The various formulations of the Henry's Law constant are shown below.
|Concentration over Pressure||Often used by Atmospheric Chemists|
|Mole Fraction over Pressure||Often taught to Chemical Engineers|
|Molality per Pressure||-|
Henry's Solubility and Henry's Volatility
The above relationships are often called Henry's solubility. When these relationships are inverted (e.g. ) they are referred to as Henry's Volatility and the inverse constant may be presented.
Henry's law was developed for real gases and liquids, but typically for low concentrations of solutes in water. Thus, the constants are generally only accurate while there is a low concentration of the component in question.
Henry's law is typically accurate along the A-B line for component 'a' in the above graph.
The table below gives some typical values for Henry's Constant for a species dissolved in water at low concentration and 298.15 K.
Refer to this compilation of values for a much more extensive list.
The factors below can be used to convert between different forms of Henry's Constant.