Page 173 - Modelling in Transport Phenomena A Conceptual Approach

6.2. CONSERVATION OF MASS 153

since mass is conserved. Equation (6.2-2) implies that the rate of production of
mass for the entire system is zero. However, if chemical reactions take place within
the system, an individual species may be produced.
On the other hand, summation of Eq. (6.1-6) over all species gives the total
mole balance as

In this case the generation term is not zero because moles are not conserved.

Example 6.2 A liquid phase irreversible reaction

A+B

takes place in a series of 4 continuous stirred tank reactors as shown in the figure
below.

The rate of reaction is given by
( *,,>
r = kcA with k=3 x 105exp --

in which k is in h-' and T is in degrees Kelvin. The temperature and the volume
of each reactor are given as follows:

Reactor Temperature Volume
No ( "C) (L)
1 35 800
2 45 1000
3 70 1200
4 60 900