Langmuir equation
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The Langmuir equation or Langmuir isotherm or Langmuir adsorption equation relates the coverage or adsorption of molecules on a solid surface to gas pressure or concentration of a medium above the solid surface at a fixed temperature. The equation was developed by Irving Langmuir in 1916. The equation is stated as:
θ or theta is the percentage coverage of the surface, P is the gas pressure or concentration, α alpha is a constant.
The constant α is the Langmuir adsorption constant and increases with an increase in the strength of adsorption and with a decrease in temperature. The equation is derived starting from the equilibrium between empty surface sites, particles and filled particle sites
equilibrium between empty surface sites S* and particles P and filled surface sites S-P
![K =\frac{[S-P]}{[S^*][P]}](../../../math/9/a/c/9acd2f7ff9780e2754811d6d786a4f4a.png)
Because the fraction of filled surface sites is equal to θ and the fraction of unfilled sites equal to 1-θ and because P is proportional to the gas pressure or concentration the equation can be rewritten to
Other equations relating to adsorption exist such as the Temkin equation or the Freundlich equation.
[edit] External links
- Langmuir isotherm @ Queen Mary, University of London Website
- Langmuir isotherm @ http://www.erpt.org Website
[edit] References
- The constitution and fundamental properties of solids and liquids. part i. solids. Irving Langmuir; J. Am. Chem. Soc. 38, 2221-95 1916 First Page
