Page 144 - Modeling of Chemical Kinetics and Reactor Design

114 Modeling of Chemical Kinetics and Reactor Design

A + { C + D (3-8)
k 1
B
k 2
The rate of the forward direction (–r ) is :
A
(–r ) = k C C (3-9)
A 1 A B
and the rate of the reverse direction (+r ) is:
A
(+r ) = k C C (3-10)
A 2 C D
The overall rate is:

(–r ) = (–r ) – (+r ) (3-11)
A net A A
The net rate of disappearance of A = k C C – k C C at
1 A B 2 C D
equilibrium where (–r ) = 0. Therefore,
A net
r
k  CC 
s =  C D  = K
1
k  CC  C (3-12)
A B Equilibrium

REACTION ORDERS

The manner in which the reaction rate varies with the concentrations
of the reactants and products can be shown by the orders of the
reaction. These are the powers to which the concentrations are raised
and are expressed as:
α β
(–r ) = kC C (3-13)
A
A
th
th
where α is the order with respect to component A, and β is the
order with respect to component B. The overall order of the reaction
n is:
n = α + β (3-14)

The exponents α and β may be integers or fractions and may be
both positive and negative values, as well as the value of zero. In some
cases, the exponents are independent of temperature. Where the