Henry's law

In chemistry, Henry's law is one of the gas laws. It states that the mass of a gas that dissolves in a definite volume of liquid is directly proportional to the pressure of the gas provided the gas does not react with the solvent. William Henry first formulated the law in 1801.

A formula for Henry's Law is:

$e^{P}=e^{kC}$

where P is the partial pressure of the gaseous solute above the solution, C is the concentration of the gas in mol/L and k is the Henry's Law constant, which has the units L*atm/mol.

Taking the natural logarithm of the formula, gives us the more commonly used formula:

$P=kC$

This version is used to showcase the effectiveness of the law for dilute solutions of gases that don't react with the solvent. Some values for k include:

• O₂ : 4.34×10⁴ atm/mol
• CO₂ : 1.64×10³ atm/mol
• H₂ : 7.04×10⁴ atm/mol

when these gases are dissolved in water at 299 kelvin. Note that the solubility coefficient varies with solvent and temperature.

Henry's law in geophysics

A version of Henry's law applies to the solubility of a noble gas in contact with silicate melt. One equation used is

$\rho _{m}/\rho _{g}=e^{-\beta (\mu _{{\rm {ex}},m}-\mu _{{\rm {ex}},g})}$

where subscripts m and g denote melt and gas phase respectively, $\rho$ the number densities of the solute gas in the melt and gas phase, $\beta =1/k_{B}T$ an inverse temperature scale ($k_{B}$ is the Boltzmann constant), $\mu _{{\rm {ex}},m}$ and $\mu _{{\rm {ex}},g}$ the excess chemical potential of the solute in the two phases.