$$x_i{H}_i=y_{i}P$$ 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 $H=\frac{y_{i}P}{x_i}$ is not a universal definition, but it is the form that has a similar form to Raoult’s Law $(x_i{P}_i^{sat}=y_{i}P)$ where $P_i^{sat}$ is the saturation pressure of species $i$.

Other ways to define Henry’s constant include: $$H_i=\frac{P}{C_i}\left(\frac{Lbar}{mol}\right)$$

$$H_i=\frac{C_i}{P}\left(\frac{mol}{Lbar}\right)$$

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

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.