[ethylenediamine]

For a CSTR, why does a species balance not include the rate of consumption and generation by chemical reaction?

It says d(C_A* V)/dt = (C_a,in)Q_in - (C_a)Q + (r_A)V

"r" is defined as r = -kC_A.

But wouldn't it be possible for r = (-k_1)C_A + (k_-1)C_A, where (k_-1)C_A represents the rate of a reverse reaction?

[Donaldson Tan]

It says d(C_A* V)/dt = (C_a,in)Q_in - (C_a)Q + (r_A)V

"r" is defined as r = -kC_A.

I think you answered your own question.

r_A is defined as the rate of formation of A per unit volume. The equation for r_A depends on the nature of the chemical reaction.

The dynamic material balance for species A in a CSTR is given by:
V_R(dC_A/dt) =F_in.C_A0 - F_out.C_A + r_A.V_R where:
1. V_R is the volume of the CSTR
2. C_A0 is the concentration of A in the feed stream
3. F refers to the flowrate.
 
For an irreversible chemical reaction A -> B + C, r_A = - rate of consumption of A = -k.C_A since A is being consumed by the reaction.

For a reversible chemical reaction, A <-> B + C, r_A = rate of generation - rate of consumption = k_b.C_B.C_C - k_f.C_A