AWM's Adsorption page - Basics - adsorption excess in non-electrolytes

A Practical Guide to Isotherms of ADSORPTION on Heterogeneous Surfaces

Adsorption basics: Liquid mixtures
Measured quantity: Adsorbed amount vs. Adsorption excess

Basics of liquid adsorption: binary liquid adsorption

Binary liquid adsorption according Everett isotherm

The picture shows comparison of surface excess, n₁^e (solid lines -----) and respective adsorption n₁^s values (dotted lines .....) for model Everett isotherm (homogeneous surface, ideal surface and bulk phase) and 3 values of adsorption constant K₁₂ = K₁ / K₂ : 10 (stronger adsorption of "1" - positive excess of "1"), 1 (equal adsorption properties of "1" and "2" - adsorption excess is 0 everywhere) and 0.1 (stronger adsorption of "2" - negative excess of "1" and positive excess of "2")

See Note on molecular sizes
Measured adsorption quantity: always surface excess, n_i^e related to true adsorption n_i^s (or a_i) by following dependences (symmetrical with respect to component exchange):
or
where superscript "l" denotes liquid, "s" surface phase, x_i is molar fraction of component "i", n^s is adsorption (n_i^s) and n^e is surface excess (n_i^e) being the total excess of component "i" in surface phase vs. bulk phase per amount of adsorbent (or adsorbent surface).

For any multicomponent system we have by definition:
$Sum of surface molar fractions$ $Sum of bulk molar fractions$
and (for equal molecular sizes - see Note):

Adsorption basics:
Gas ( Basics )
Non-electrolyte liquids ( Basics, Everett iso., linear plots, heterogeneity )
Dilute solutions ( Dilute solutions )

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