Page 51 - Modeling of Chemical Kinetics and Reactor Design

Reaction Mechanisms and Rate Expressions 21

4. Chain termination
(a) Radical combination

(
RM) → (
RM) * + ( k tc RM) ( ) (1-91)

M R
m n m n
(b) Radical disproportionation
(
R M) + ( k tD → saturated polymer
R M) 
*
m n (1-92)
+ unsaturated polymer
CATALYTIC REACTIONS

ENZYME CATALYZED REACTIONS

Enzymes are proteins of high molecular weight and possess excep-
tionally high catalytic properties. These are important to plant and
animal life processes. An enzyme, E, is a protein or protein-like
substance with catalytic properties. A substrate, S, is the substance that
is chemically transformed at an accelerated rate because of the action
of the enzyme on it. Most enzymes are normally named in terms of
the reactions they catalyze. In practice, a suffice -ase is added to the
substrate on which the enzyme acts. For example, the enzyme that
catalyzes the decomposition of urea is urease, the enzyme that acts
on uric acid is uricase, and the enzyme present in the micro-organism
that converts glucose to gluconolactone is glucose oxidase. The three
major types of enzyme reaction are:

Soluble enzyme–insoluble substrate
Insoluble enzyme–soluble substrate
Soluble enzyme–soluble substrate

The study of enzymes is important because every synthetic and
degradation reaction in all living cells is controlled and catalyzed by
specific enzymes. Many of these reactions are the soluble enzyme–
soluble substrate type and are homogeneous in the liquid phase.
The simplest type of enzymatic reaction involves only a single
reactant or substrate. The substrate forms an unstable complex with
the enzyme that decomposes to give the product species or, alter-
natively, to generate the substrate.