D. A. Rockstraw, Ph.D., P.E.
NEW MEXICO STATE UNIVERSITY
Department of Chemical Engineering
Ch E 441 Chemical Kinetics and Reactor Engineering
Quiz 10 Closed Book/Notes
Derive the Langmuir isotherm for adsorption of species A in a non-reacting system. Let
the assumptions inherent in the solution.
SOLUTION
Assume
•monolayer coverage of surface
•uniform surface
•Interaction between gas/site only
Stoichiometry defined as: A + S ↔ A•S
Rate of adsorption (forward reaction): vAAad CPkr A
=
Rate of desorption (reverse reaction): SAAde Ckr A•−
=
Net rate at equilibrium: ⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛−= •
A
SA
vAAda K
C
CPkr A
/
Site balance: SAvt CCC •
+
=
Solve for CA•S, and substitute for Cv:
AA
tAA
SA PK
CPK
C+
=
•1