Case 2: Rate is adsorption control

(a)  Adsorption of A controlling

Let adsorption of A be the slowest step so that adsorption of B, surface reaction and desorption of C are at equilibrium.

Adsorption of A is given as

.............................

(6)

Now as other steps are in equilibrium:

Substituting value in equation (6)

(7)

= Overall equilibrium constant.

Substituting value of C_V in equation (7)

(8)

 

For a given catalyst C₀ is constant.

Similarly expression when desorption of product is the rate controlling step can be derived. For desorption of C controlling the whole reaction, the rate expression can be derived as