\[x_iH_i \, = \, y_iP\] where \(H_i \, = \) Henry’s constant (bar), which varies with temperature, \(x_i \, = \) the mole fraction of component \(i\) dissolved in a liquid, \(y_i \, = \) the mole fraction of component \(i\) in the gas phase, and \(P \, = \) pressure (bar).

One form for the Henry’s constant temperature dependence is: \[H\,=\,\frac{1}{exp(A+\frac{B}{T}+ClnT+DT)}\] where \(A, B, C, D\) are constants specfic to each species, and \(T = \) temperature (K)

Defining Henry’s constant as \(H = \frac{y_iP}{x_i}\) is not a universal definition, but it is the form that has a similar form to Raoult’s Law \((x_iP_i^{sat} = y_iP)\) where \(P_i^{sat}\) is the saturation pressure of species \(i\).

Other ways to define Henry’s constant include: \[H_i = \frac{P}{C_i}\left(\frac{L\, bar}{mol}\right)\]

\[H_i = \frac{C_i}{P}\left(\frac{mol}{L\, bar}\right)\]

\[H_i = \frac{C_i}{C_{i,gas}} (dimensionless)\]

where \(C_i\) is the concentration of species \(i\) in the liquid, and \(C_{i,gas}\) is the concentration of species \(i\) in the gas phase.