Hertz–Knudsen equation
In surface chemistry, the Hertz–Knudsen equation, also known as Knudsen-Langmuir equation describes evaporation rates, named after Heinrich Hertz and Martin Knudsen.
Applications
Non-dissociative adsorption (Langmuirian adsorption)
The Hertz–Knudsen equation describes the sticking of gas molecules on a surface by expressing the time rate of change of the concentration of molecules on the surface as a function of the pressure of the gas and other parameters:where:
| Quantity | Description |
| A | Surface area |
| N | Number of gas molecules |
| φ | Flux of the gas molecules |
| α | Sticking coefficient of the gas molecules onto the surface, 0 ≤ α ≤ 1 |
| p | The gas pressure |
| M | Molar mass |
| m | Mass of a particle |
| kB | Boltzmann constant |
| T | Temperature |
| R | Gas constant |
| NA | Avogadro constant |