Page 326 - Elements of Chemical Reaction Engineering Ebook

Sec. 6.3 Algorithm for Solution to Complex Reactions 297
tions. That is, the net rate of reaction for species Aj is the sum of all rates of
reaction in which species Aj appears. For q reactions taking place,
rj = c rij 1
4

i= 1 (6- 16)

6.3.3 Rate Laws
The rate Aaws for each of the individual reactions are expressed in terms
of concentrations, Cj, of the reacting species. For example, if reaction 2 above
(i.e., A + 2C 43E) followed an elementary rate law, then the rate of disap-
pearance of A could be

or in terms of the rate of formation of A in reaction 2,

For the general reaction set given in Table 6-2, the rate law for the rate of for-
mation of reactant species A, in reaction i might depend on the concentration
of species A, and species Aj , for example,

We need to determine the rate law for at least one species in each reaction.

6.3.4 Stoichiometry: Relative Rates of Reaction

The next step is to relate the rate law for a particular reaction and species
to other species participating in that reaction. To achieve this relationship we
simply recall the generic reaction from Chapters 2 and 3,

aA+bB cC+dD (2-1)
and use Equation (2-20) to relate the rates of disappearance of A and B to1 the
rates oE formation of C and D:

In working with multiple reactions it is usually more advantageous to relate
the rates of formation of each species to one another. This can be achieved by
rewriting (2-20) in the form for reaction i
helative rates of (6- 17)
reaction

-
r2,
e.g. for reaction 2: rZc = - - a2 c2 ( -r2*)
c2
- a2