Explains the concept of adsorption and derives the Langmuir isotherm.

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

An introduction to Langmuir Isotherms.

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

Optional screencast: Langmuir Isotherm: Dissociative Adsorption

##### Important Equations:

Langmuir isotherm for species A adsorbed on a surface:

$\theta _A = \frac{K_AP_A}{1 + K_AP_A}$

where $$K_A$$ = adsorption equilibrium constant for species A,

$$P_A$$ = pressure of species A, and

$$\theta _A$$ = fraction of the surface covered by species A.

The Lanmuir isotherm for molecules A and B co-adsorbed has the form:

$Molecules \,\, of \,\, A\,\, adsorbed/site\,\,= \frac{K_AP_A}{1+K_AP_A + K_BP_B}$

$Molecules \,\, of \,\, B\,\, adsorbed/site\,\,= \frac{K_BP_B}{\alpha (1+K_AP_A +K_BP_B)}$

where $$K_B$$ = adsorption equilibrium constant for species B,

$$P_B$$ = pressure of species B, and

$\alpha = \frac{sites\,\,needed\,\,for\,\,B}{sites\,\,needed\,\,for\,\,A}$

$K_A = K_{A0}exp \left( \frac{-\Delta H}{RT} \right)$

where $$\Delta H$$ = enthalpy change on adsorption, which is negative because adsorption is exothermic.

$$K_{A0}$$ is a temperature-independent term.

$\theta _H = \frac{K^{0.5} _{\alpha} P^{0.5} _{H_2}}{1+K^{0.5} _{\alpha} P^{0.5} _{H_2}}$
where $$\theta _H$$ = fraction of sites covered by H atoms
$$K_{\alpha}$$ = adsorption equilibrium constant, and
$$P_{H_2}$$ = H2 pressure.