Engineering Chemistry S Datta

142 ENGINEERING CHEMISTRY
intermediate compound is an activated complex formed on the catalyst surface. The
adsorption theory can be explained by the following Fig. 6.3.
H
H
H
H
Ni Ni Ni Ni
(a) Adsorption of H 2
molecule
H
H
C C
H
H
H H
Ni Ni Ni Ni
(b) H–H bond weakened and broken
by chemisorption
H
H
H C C H
H
H
+
Ni Ni Ni Ni
Ni Ni Ni Ni
(c) Formation of activated
(d) The product ethane released
complex with ethene.
from catalyst surface.
Fig. 6.3 (a), (b), (c) and (d).
Biochemical Catalysts (Enzymes)
Numerous organic reactions occur in the body of living beings, either plants or animals,
to maintain the life processes. These reactions are catalysed by certain organic compounds
which are known as biocatalysts or enzymes.
Enzymes are invariably protein molecules. But not all protein molecules are enzymes.
This statement can be explained by the fact that those protein molecules containing an active
site are enzymes. The protein molecules, which do not contain those active sites cannot function
as enzymes. It is assumed that enzymes act on a substrate to give products. The following
figure explains the enzymatic activity:
Enzymatic activity can be explained as:
Enzyme + Substrate Enzyme – Substrate ⎯⎯→ Products + Enzyme
[activated complex]
The reaction is abbreviated as:
E + S E – S ⎯⎯→ P + E.
where E = enzyme, S = substrate (reactant),
ES = activated complex,P = products.
The reaction may be represented pictorially as follows (Fig. 6.4).
S
+
E
ES
[activated complex]
+
E
Active sites
Products
Fig. 6.4 Illustration of the lock-and-key model of enzyme catalysis.