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Langmuir adsorption isotherm


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An equation used to describe the amount of gas adsorbed on a plane surface, as a function of the pressure of the gas in equilibrium with the surface. The Langmuir adsorption isotherm can be written:θ=bp/(1+bp), where θ is the fraction of the surface covered by the adsorbate, p is the pressure of the gas, and b is a constant called the adsorption coefficient, which is the equilibrium constant for the process of adsorption. The Langmuir adsorption isotherm was derived by the US chemist Irving Langmuir (1881–1957), using the kinetic theory of gases and making the assumptions that: (1) the adsorption consists entirely of a monolayer at the surface; (2) there is no interaction between molecules on different sites and each site can hold only one adsorbed molecule; (3) the heat of adsorption does not depend on the number of sites and is equal for all sites. The Langmuir adsorption isotherm is of limited application since for real surfaces the energy is not the same for all sites and interactions between adsorbed molecules cannot be ignored.

θ=bp/(1+bp)

(1) the adsorption consists entirely of a monolayer at the surface; (2) there is no interaction between molecules on different sites and each site can hold only one adsorbed molecule; (3) the heat of adsorption does not depend on the number of sites and is equal for all sites.

Subjects: Chemistry.


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