Page 439 - Elements of Chemical Reaction Engineering Ebook

41 0 Nonelernentary Reaction Kinetics Chap. 7

QUESTIONS AND PROBLEMS

The subscript to each of the problem numbers indicates the level of difficulty: A, least
difficult; D, most difficult.
A=@ B=lL Cr+ D=++
In each of the questions and problems below, rather than just drawing a box .around
your answer, write a sentence or two describing how you solved the problem, the assump-
tions you made, the reasonableness of your answer, what you learned, and any other facts
that you want to include. You may wish to refer to W. Strunk and E. B. White, The Ele-
ments of Style (New York: Macmillan, 1979) and Joseph M. Williams, Style: Ten Lessons
in Clarity & Grace (Glenview, 111.: Scott, Foresman, 1989) to enhance the quality of your
sentences. See the Preface for additional generic parts (x), (y), (z) to the home problems.
P7-lc Read over all of this chapter’s problems. Make up an original problem that
uses the concepts presented in this chapter. To obtain a solution:
(a) Make up your data and reaction.
(b) Use a real reaction and real data.
See R. M. Felder, Chem. Eng. Educ., 19(4), 176 (1985).
W-2A What if.. .
(a) you carried out the ethane reaction in Example 7-2 at 1500 K or 2000 K?
Would the PSSH still be valid? Can you find a temperature at which the
PSSH is not a good approximation? Explain.
[Hint: Calculate different ratios of radicals (e.g., CH,*/H*, CH, */C2H5*, etc.).]
(b) you could choose from a number of different initiators (Z2 ko > 21):
fast to slow, ko = 0.01 s-l, ko = 0.0001 s-’, and ko = 0.00001 s-l, and
initiator concentrations, IO-’ to lod5 M? What would guide your selec-
tion? (Hint: Plot M vs. t.)
(c) the enzymatic reaction in Example 7-7 were exothermic? What would be
the effect of raising or lowering the temperature on the rate law parame-
ters on the overall rate?
(d) the enzymatic reaction in Example 7-8 were carried out in a CSTR with
a space time of 400 s? What conversion would be achieved? How would
your answer change for two CSTRs in series, with T = 200 s for each?
What if both the total enzyme concentration and the substrate concentra-
tion were increased by a factor of 4 in the CSTR with T = 400 S?
(e) you were asked to carry out the bioreaction in Example 7-9 at higher and
lower temperatures? What do you think the substrate, cell, and product
concentrations would look like? Sketch each as a function of time for dif-
ferent temperatures. Discuss the reasonableness of assumptions you made
to arrive at your curves. What is the relationship between C; and Ypls €or
which the final cell concentration is invariant? Can an equation for the
washout dilution rate be derived for the Tessier Eqn.? If so what is it?
W-3, (Flame retardants) Hydrogen radicals are important to sustaining combustion
reactions. Consequently, if chemical compounds are introduced that can scav-
ange the hydrogen radicals, the flames can be extinguished. While many reac-
tions occur during the combustion process, we shall choose CO flames as a
model system to illustrate the process [S. Senkan et al., Combustion and
Flame, 69, p. 113 (1987)l. In the absence of inhibitors
o2 ___) o.+o. (W-3.1)