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adsorption isotherm

An equation that describes how the amount of a substance adsorbed onto a surface de­pends on its pressure (if a gas) or its concentration (if in a solution), at a constant temperature. Several ad­sorption isotherms are used in sur­face chemistry including the BET isotherm and the Langmuir ad­sorption isotherm. The different isotherms correspond to different as­sumptions about the surface and the adsorbed molecules.