Page 80 - Introduction to chemical reaction engineering and kinetics

62 Chapter 3: Experimental Methods in Kinetics: Measurement of Rate of Reaction

the limiting values of k and slopes. At what temperature (in terms of EA) does this curve have
an inflection point? Based on typical values for EA (say 40,000 to 300,000 J mol-‘), would
this temperature lie within the usual “chemical” range? Hence, indicate what part (shape) of
the curve would typify chemical behavior.
3-6 Suppose the liquid-phase reaction A + 1Yg IB --f products was studied in a batch reactor at two

temperatures and the following results were obtained: _

TI"C fA tlmin

20 0.75 20
30 0.75 9

Stating all assumptions made, calculate EA, the Arrhenius energy of activation, for the reac-
tion. Note that the order of reaction is not known.
3-7 What is the expression corresponding to equation 3.4-13 for the same type of reaction (I VA[A +
I V~/B + products, constant density) occurring in a CSTR of volume Vwith a steady-state flow
rate of q?
3-8 By applying L’HBpital’s rule for indeterminate forms, show that equation 3.4-11 results from
equation 3.4-9.
3-9 The reaction between ethylene bromide and potassium iodide in 99% methanol (inert) has
been found to be first-order with respect to each reactant (second-order overall) (Dillon, 1932).
The reaction can be represented by C&L,Br2 + 3Kl +C2&+2KBr+KIsorA+3B +
products.
(a) Derive an expression for calculating the second-order rate constant kA (the equivalent of
equation 3.4-13).
(b) At 59.7”C in one set of experiments, for which CA0 = 0.0266 and ca,, = 0.2237 mol L-l,
the bromide (A) was 59.1% reacted at the end of 15.25 h. Calculate the value of kA and
specify its units.
3-10 A general rate expression for the irreversible reaction A + B + C can be written as:

Use a spreadsheet or equivalent computer program to calculate the concentration of product
C as the reaction proceeds with time (t) in a constant-volume batch reactor (try the parameter
values supplied below). You may use a simple numerical integration scheme such as Act =
rc At.

set 1: simple rate laws:
CAo CBo CC0 k a P Y
(a) 1 1 0 0.05 1 0 0
(b) 1 1 0 0.05 1 1 0
(c) 1 1 0 0.025 1 1 0
(d) 1 2 0 0.025 1 1 0
set 2: more complicated rate laws:
69 1 1 0.0001 0.05 1 0 1
(0 1 1 0.0001 0.005 1 0 - 1

Observe what is happening by plotting cc versus t for each case and answer the following:
(i) Qualitatively state the similarities among the different cases. Is component B in-
volved in the reaction in all cases?