Freundlich equation
From Wikipedia, the free encyclopedia
The Freundlich Adsorption Isotherm is an adsorption isotherm, which is a curve relating the concentration of a solute on the surface of an adsorbent, to the concentration of the solute in the liquid with which it is in contact.
The Freundlich Adsorption Isotherm is mathematically expressed as
- <math>\ x/m=Kp^{1/n}</math>
OR
- <math>\ x/m=KC^{1/n}</math>
- Where
- x = mass of adsorbate
- m = mass of adsorbent
- P = Equilibrium pressure of adsorbate
- c = Equilibrium concentrate of adsorbate in solution.
K and 1/n are constants for a given adsorbate and adsorbent at a particular temperature.
There are basically two well established types of adsorption isotherm:
- the Langmuir adsorption isotherm
- the Freundlich adsorption isotherm
The Langmuir adsorption isotherm describes quantitatively the build up of a layer of molecules on an adsorbent surface as a function of the concentration of the adsorbed material in the liquid in which it is in contact. In a modified form it can also describe a bi-layer deposition. The shape of the isotherm (assuming the (x) axis represents the concentration of adsorbing material in the contacting liquid) is a gradual positive curve that flattens to a constant value. The Freundlich isotherm curves in the opposite way and is exponential in form. It often represents an initial surface adsorption followed by a condensation effect resulting from extremely strong solute-solute interaction. In chromatography the Freundlich isotherm is not common, most adsorption processes are best described by the Langmuir isotherm.
