PHYSICAL CHEMISTRY IN BRIEF

CHAP. 9: CHEMICAL KINETICS [CONTENTS] 328

not the rate-determining process. If the diffusion is slow, the transport may be accelerated by
mixing.

9.8.3.2 Adsorption and desorption.

These processes are considered to be in equilibrium and they are discussed in chapter Physical
chemistry of surfaces.

9.8.3.3 Chemical reaction

Let’s assume the following reaction taking place on the catalyst surface

A

→kA

←

kB

B

The rate of the reaction is given by the kinetic equation

−

dθA

dτ

=kAθA−kBθB, (9.172)

whereθiis the surface concentration of substancei. Surface concentrations may be determined
e.g. from the Langmuir adsorption isotherm, see equations (13.39).

Note: The only difference between kinetic equations for reactions on the surface of the

solid phase and common kinetic equation is that in the former case we write surface

concentrations, i.e. amounts of substance, related to unit surface.

9.8.4 Enzyme catalysis

The Michaelis-Menten mechanism models the reaction of a reactant (substrate) S to product
P amid the catalytic effect of enzyme E in the following way

E + S

→k^1

←

k 2

ES

k 3

→ E + P, (9.173)