D. A. Rockstraw, Ph.D., P.E.
NEW MEXICO STATE UNIVERSITY
Department of Chemical Engineering
Ch E 441 Chemical Kinetics and Reactor Engineering
Quiz 7 & 8 Closed Book/Notes
Consider the liquid-phase, elementary reactions CBA rxnrxn 2
2 1 ⎯⎯→←⎯⎯→← which are
being carried out in a batch reactor. The reaction rate constants are as follows: k1Af = 3
min-1, k1Br = 1 min-1, k2Bf = 0.5 min-1 and k2Cr = 0.25 min-1. The three components of each
subscript on the rate constants identify (1) reaction number, (2) species upon which the
rate law is based, and (3) whether the constant if for the forward or reverse step. The
initial concentration of A is 1 M.
(7) In class: Set up the mathematics of the solution to this problem. Show all species
mole balances with the appropriate net rate law substituted into each. Be sure to apply
the stoichiometric coefficients where necessary.
(8) Take home (due at the Ch E Office by noon tomorrow): Solve the system of
equations (corrected if necessary). Identify (i) the maximum concentration of
intermediate species B, (ii) how long after the start of the reaction this maximum occurs,
and (iii) the steady-state concentration of each species.
SOLUTION
Mole Balances with net rate laws
A:
()
BBrAAf
Br
b
a
Af
A
CkCk
rr
dt
dC
11
11
+−=
+=
B:
() ()
()
()
()
CCrBBfBrAAf
CCrBBfBBrAAf
Cr
c
b
BfBrAf
b
a
B
CkCkkCk
CkCkCkCk
rrrr
dt
dC
2
2
1
211
2
2
1
211
2211
++−=
+−−=
+++=
C:
:
()
CCrBBf
CrBf
b
c
C
CkCk
rr
dt
dC
22
22
2−=
+=
