Page 25 - Introduction to chemical reaction engineering and kinetics

1.4 Aspects of Kinetics 7

Thermowells I

Catalyst
Catalyst
basket
basket

Impeller
Impeller

Figure 1.2 Laboratory flow reactor for solid-catalyzed gas-
reactor
for
flow
1.2

Laboratory
solid-catalyzed

gas-
Figure
phase reaction (schematic adapted from Mahoney, 1974)
phase reaction (schematic adapted from Mahoney, 1974)
tion stating that the amount of that element is fixed, no matter how combined or re-
combined, and regardless of rate of reaction or whether equilibrium is attained.
Alternatively, e conservation of atomic species is commonly expressed in the form
of chemical equati
Tns, corresponding to chemical reactions. We refer to the stoichio-
metric constraints expressed this way as chemical reaction stoichiometry. A simple
system is represented by one chemical equation, and a complex system by a set of
chemical equations. Determining the number and a proper set of chemical equations
for a specified list of species (reactants and products) is the role of chemical reaction
stoichiometry.
The oxidation of sulfur dioxide to sulfur trioxide in the manufacture of sulfuric acid is
an example of a simple system. It involves 3 species (SO,, 0, and SO,) with 2 elements
(S and 0). The stoichiometry of the reaction can be represented by one, and only one,
chemical equation (apart from a multiplicative factor):

2 so, + 0, = 2 so, (A)
or

-2so,-0,+2so, = 0 09

Equation (A) or (B) stems from the fact that the two element balances involve three quan-
tities related to amounts of the species. These balances may be written as follows:

For S:

lAnSOz + OAnOz + lAnso = 0 (Cl
3
For 0:

2Anso2 + 2Ano, + 3AnSo3 = 0 (D)