#### Absorption and Henry's Law: Screencast

Explains why Henry’s law is used and shows how Henry’s constant is used.

We suggest you list the important points in this screencast as a way to increase retention.

##### Important Equations:

$x_iH_i \, = \, y_iP$ 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.