Module 6 : Reaction Kinetics and Dynamics
Lecture 27 : Experimental methods in chemical kinetics
 27.8
 Problems

27.1)

List the names of a few molecules which are levorotatory and dextrorotatory. Do they all have to have
  asymmetric carbon atoms?
   
27.2)
 Among the following, which one has the highest value of molar conductance, KCl, NaCl, HCl and CH3F ? List
  them in the decreasing order of molar conductivity.
   
27.3)
In a flash photolysis experiment a beam is split into two by a beam splitter. A part of the beam goes directly to
  the reaction cell. Another part goes through a longer path (reflected by a mirror, passed through a fluorescent solution which converts the beam into continuous radiation in the visible range so that this can be used to analyse the products) so that it can reach the reaction vessel after a time delay to analyse the products. For a time delay of 10-7s, the additional path to be traveled by the second analysing beam is c * t = 2.988 * 1010cm/s * 10 -7 s = 2998cm. What is the smallest time delay that can be achieved in this set up?
   
27.4)
 Can you suggest ways for determining the rates of the following reactions?
a)
 2 NO(g) + 2H2(g) N2(g) + 2H2O(g)
b)
 A reaction with a half life of 10-10s
c)
 S2O2-4(aq) + I2- (aq) 2SO42-(aq) + I 2 (aq), and
d)
 Bromination of CH3COCH3
   
27.5)
 Conductance measurements were used to study the hydrolysis of CH3COOCH3 by NaOH at 25 o C in the
  reaction NaOH + CH3COOCH3 COONa + H2O The initial concentrations of both the reactants were 0.004 mol / lit. The molar conductivity at different times was measured as follows
 

Time (in minutes)

1000 * (in ohm –1 cm –1)

0

1.24

10

1.04

20

0.92

30

0.84

40

0.78

(very large times)

0.44

  Initially the conductivity is mainly due to OH- and at the end, the conductivity is mainly due to CHCOO- ions. Find the concentrations of OH - and CH3COO - as a function of time. Determine the reaction order with respect to OH - by plotting log [ a/ (a-x) ] vs time.
   
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