A law that states the effect of change of pressure on the solubility of a gas in a solvent. The law takes the form that the mass of a given gas which saturates a given solvent is directly proportional to the pressure of the gas at equilibrium, provided that the temperature is constant and that the gas does not react chemically with the solvent:
where pA is the partial pressure of component A, H is Henry’s law constant, and xA is the mole fraction of the component in the solvent. It is used for many gases to describe the relationship between the concentration of a gas dissolved in a liquid and the equilibrium partial pressure. It does not apply to the aqueous behaviour of very soluble gases, and slight inaccuracies also arise because gases do not obey Boyle’s law exactly. The SI units for H are pascals per mole fraction. It was formulated in 1803 by English chemist William Henry (1774–1836).