Non-dissociative adsorption (Langmuirian adsorption) The Hertz–Knudsen equation describes the non-
dissociative adsorption of a
gas molecule on a surface by expressing the variation of the number of molecules impacting on the surfaces per unit of time as a function of the pressure of the gas and other parameters which characterise both the gas phase molecule and the surface: :\frac{\mathrm{d}N}{A \mathrm{d}t} \equiv \varphi = \frac{\alpha p}{\sqrt{2\pi m k_\text{B} T}} = \frac{\alpha p N_A}{\sqrt{2\pi M RT}}, where: Since the equation result has the units of s−1 per area, it can be assimilated to a rate constant for the adsorption process. ==See also==