The fundamental thermodynamic equation describing adsorption from solution is Gibbs adsorption isotherm, which relates the excess concentration of solute at the surface to the activity of the solute in solution. Applications of this theorem require the utmost purity of components and is therefore seldom applied to more than two components. Measurements of surface tension as a function of activity at constant temperature can therefore lead to two-dimensional equations of state. The surface-tension isotherms of members of a homologous series results in Traube’s rule that the surface activity increases geometrically as the chain length increases linearly.
Key Words: adsorption isotherm, Frumkin equation, Gibbs adsorption, Gibbs
dividing surface, Langmuir equation, standard state, surface equation
of state, Szyszkowski equation, Traube’s rule
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