Hertz–Knudsen equation
Appearance
In surface chemistry, the Hertz–Knudsen equation, also known as Knudsen-Langmuir equation describes evaporation rates, named after Heinrich Hertz and Martin Knudsen.
Definition
[edit]Non-dissociative adsorption (Langmuirian adsorption)
[edit]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:[1][2]
where:
Quantity | Description |
---|---|
A | Surface area (in m2) |
N | Number of gas molecules |
t | Time (in s) |
Flux of the gas molecules (in m−2 s−1) | |
Sticking coefficient of the gas molecules onto the surface, 0 ≤ | |
p | The gas pressure (in Pa) |
M | Molar mass (in kg mol−1) |
m | Mass of a particle (in kg) |
kB | Boltzmann constant |
T | Temperature (in K) |
R | Gas constant (J mol−1 K−1) |
NA | Avogadro constant (mol−1) |
Since the equation result has the units of s-1 it can be assimilated to a rate constant for the adsorption process.
See also
[edit]References
[edit]- ^ Kolasinski, Kurt W. (2012). Surface Science: Foundations of Catalysis and Nanoscience, Third Edition. p. 203. doi:10.1002/9781119941798.
- ^ R. B. Darling, EE-527: Micro Fabrication, Virginia University (retrieved Feb. 9 2015).