**Howard P. Isermann Department of Chemical and Biological Engineering**

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## B.E.T. Equation

A different equation is more likely to describe adsorption
where the adsorbate exceeds a monolayer. The Brunauer-Emmett-Teller (BET)equation is:

where C_{s} = concentration at which all layers are filled

K_{b} = a coefficient

Its assumptions are:

- Adsorbed molecules stay put
- Enthalpy of adsorption is the same for any layer
- Energy of adsorption is the same for layers other than the first
- A new layer can start before another is finished.

It is important that many unusual adsorption isotherms are fitted well bythe BET equation. This is to be expected when there are three coefficients to manipulate.
The maximum loading, Q_{m}, just multipiles to move the entire curve up and down.
The coefficient, K_{b}, has a major effect on shape. The concentration at which
all sites are saturated (maybe several layers) can be adjusted to get a portion of the
isotherm. In other words, you can look at just part of the curve. As C approaches
C_{s}, the denomenator of the equation becomes small, and the curve shoots up.
### Plotting the B.E.T. Equation with Various Coefficients

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