velocities at entrances and exits, one must be very careful about the general use of this approximation. If Eq. 4‐61 were true for all species under all conditions, there would be no separation, no purification, no mixing, and no chemical reactions!
Under certain circumstances we may want to use a total mole balance and this is obtained by summing Eq. 4‐17 over all N species in order to obtain (4‐62)
Use of the definitions given by Eqs. 4‐28 and 4‐56 allows us to write this sult re
Here we should note that the overall net rate of production of moles need not be zero, thus the overall mole balance is more complex than the overall mass balance.
4.5 Molar Flow Rates at Entrances and Exits
Here we direct our attention to the macroscopic mole balance for a fixed ontrol