Reaction on surfaces

In the case of a solid immersed in a solution, the reactants in the solution must diffuse to the interface, get adsorbed there and participate in a given reaction mechanism on the solid surface. The product on the surface must then desorb and diffuse into the solution.

Consider the surface catalysis of isomerisation or dissociation of a substance A on surface S as follows. The substance S gets adsorbed on the surface forming AS and then dissociates into products.

A + S AS

AS Product

Reaction velocity,

Where,

If, and represents the surface sites covered by A, then
C_AS = C_s
or, reaction velocity,

= k₂ C_s

Let C_a = concentration of A either in gas or solution
Since C_s is constant, it can be incorporated into the rate constant

A plot of yields as the intercept and as the slope.