1. Complexity of Growth & Decline Delayed Consequences and Oscillations
Rainer Glaser, Chemistry
MLS Proseminar, November 16, 2009
(with updates)

4. Chemical Reaction Kinetics
Landolt Iodine Clock Reaction (Chem. Ber., 1885)
Belousov-Zhabotinsky Reaction (Nature, 1970)
Briggs-Rauscher Reaction (J. Chem. Educ., 1973)
Organization of Activities
1. Meeting, 11/16: Chemistry Background, Lecture, Dr. Glaser
2. Meeting, 11/30: Experiments by 4 Student Groups, Dr. Glaser & Ms. Miller
2 Student Groups perform Landolt and Briggs-Rauscher Reactions
2 Student Groups perform Landolt and Belousov-Zhabotinsky Reactions
3. Meeting, 12/7: Mathematical Simulation, Dr. Chicone
Focus on Lengyel Reaction, a Briggs-Rauscher-type Reaction

5. Simple Chemical Kinetics: Differential Form
Zero-Order Reaction (red)
The rate of reaction is a constant. When the limiting reactant is completely consumed, the
reaction abruptly stops.
Differential Rate Law: r = k
Unit of k: mole L-1 sec-1
First-Order Reaction (green)
The rate of reaction is directly proportional to the concentration of one of the reactants.
Differential Rate Law: r = k [A]
Units of k: sec-1
Second-Order Reaction (blue)
The rate of reaction is directly proportional to the square of the concentration of one of the
reactants.
Differential Rate Law: r = k [A]2
Units of k: L mole-1 sec-1

6. Simple Chemical Kinetics

7. http://www. chemie. uni-regensburg
Organic Chemistry Demonstration Experiments on Video Chemistry Visualized Peter Keusch, University of Regensburg

8. Landolt Iodine Clock Reaction
How to recognize starch in your food…
And then my friendly local chemist reminded me of the easy test for starch: simply drop iodine onto the suspect food. If it contains starch, the color of the iodine will darken from orange to shades ranging from inky blue to black.
The Element Iodine
Iodine is a bluish-black, lustrous solid. It volatilizes at ambient temperatures into a pretty blue-violet gas with an irritating odor.

9. Landolt Iodine Clock Reaction
Starch
Amylose and Amylopectin
Glucose Polymers

10. Landolt Iodine Clock Reaction
Bisulfite reduces Iodate to Iodine (Overall)
5 HSO IO H HSO I2 + H2O
If this were a simple reaction, then one would expect that iodine is formed as soon as the bisulfite and iodate solutions are mixed.
Instead, the experiment shows that the iodine concentration [I2] remains below detection limit until [I2] builds up, quite suddenly, after a delay time t.
Now watch the video (requires Real Player).

11. Landolt Iodine Clock Reaction
Bisulfite reduces Iodate to Iodide (LR1)
3 HSO IO HSO I-
Iodate reacts with Iodide to Iodine (LR2)
5 I- + IO H I H2O
Bisulfite reduces Iodine to Iodide (LR3)
I2 + HSO H2O I- + HSO H+
Iodine-Iodide-Starch Complex Formation (LR4, fast!)
x I2 + y I- + amylose blue complex
Symproportionation

12. Landolt Iodine Clock Reaction
Iodate (+V) Iodine (0) Iodide (-I)
IO I I-
LR1 - slow
LR2 - fast
LR3 - very fast
While LR1 and LR3 occur:
[1] Iodate concentration continuously decreases
[2] Iodide concentration increases, then collapses
[3] Iodine concentration cannot build up until bisulfite consumed

13. Landolt Iodine Clock Reaction
Stoichiometry: 5 bisulfite for every 2 iodate.
Solution A (1 L) contains 1.16 g NaHSO3. Solution B (1 L) contains 4.3 g KI.
MW(NaHSO3) = 104 g/mol; MW(KI) = 166 g/mol
50 mL of solution A contain 1.16/20 g NaHSO3, or 0.56 mmol.
50 mL of solution B contain 4.3/20 g KI, or 1.3 mmol.
25 mL of solution B contain 0.65 mmol.
Our conditions: Not stoichiometric. Excess of iodate.
We will run out of bisulfite for sure!
The slow reaction LR1 depends on the concentration of iodate.
Rate of reaction LR1 = kLR1 [HSO3-]m [IO3-]
The faster LR1, the faster we will run out of bisulfite!

14. Landolt Iodine Clock Reaction
Church-Dreskin Induction Period
On the Kinetics of Color Development in the Landolt (“Iodine Clock”) Reaction.
Church, J. A.; Dreskin, S. A. J. Phys. Chem. 1968, 72,

15. Refs from
Sobel, 2006.

16. Belousov-Zhabotinsky Reaction
“unstirred”
Rings or Spirals!
Click here for a great video
(requires Real Player).
Click here to see the video of the “stirred” BZ Reaction
(requires Real Player).

17. Belousov-Zhabotinsky Reaction
[Fe(o-phen)3]2+
Ferroin
Bromate (+V), BrO3-
Bromite (+III), BrO2-
Hypobromite (+I), BrO-
Bromide (-I), Br-
[(Ce3+)(NH4+)2(NO3-)5]
[Fe(o-phen)3]3+
Ferriin
Oscillations in Chemical Systems. I. Detailed Mechanism in a System Showing Temporal Oscillations.
Noyes, R. N.; Field, R. J.; Koros, E. J. Am. Chem. Soc. 1972, 94,

18. Belousov-Zhabotinsky Reaction Noyes-Field-Koros Model
Bromination of Malonic Acid with Bromate and in the presence of Bromide
BrO3- + Br H HBrO2 + HOBr (R3) slow
HBrO2 + Br- + H HOBr (R2)
HOBr + Br- + H Br2 + H2O (R1)
Br2 + MA BMA + HBr (R8)
BrO Br MA H BMA H2O (A)
[HBrO2]A = k3/k2 [BrO3-][H+] = 510-10 [BrO3-][H+] (1)
Lots of Br-, lots of Br2 production.

19. Belousov-Zhabotinsky Reaction Noyes-Field-Koros Model
Bromination of Malonic Acid with Bromate and in the absence of Bromide
BrO3- + HBrO2 + H BrO2 + H2O (R5) slow
BrO2 + Ce3+ + H HBrO2 + Ce4+ (R6)
2 HBrO BrO HOBr + H+ (R4)
HOBr + MA BMA + H2O (R8a)
BrO Ce3+ + MA + 5 H BMA + 4 Ce H2O (B)
[HBrO2]B = k5/2k4 [BrO3-][H+] = 110-4 [BrO3-][H+] (2)
[HBrO2] is 100,000 times higher compared to process A!
Independent of [Br-].

20. Belousov-Zhabotinsky Reaction Noyes-Field-Koros Model
The Bromide Switch
BrO Br MA H BMA H2O (A)
[HBrO2]A = k3/k2 [BrO3-][H+] = 510-10 [BrO3-][H+] (1)
Lots of Br-, lots of Br2 production. Keeps [HBrO2] low.
BrO Ce3+ + MA + 5 H BMA + 4 Ce H2O (B)
[HBrO2]B = k5/2k4 [BrO3-][H+] = 110-4 [BrO3-][H+] (2)
Independent of [Br-].
[Br-]crit = k5/k2 [BrO3-] = 310-6 [BrO3-] (3)
Now we know why solutions reacting by (A) will turn themselves into solutions reacting by (B).

21. Belousov-Zhabotinsky Reaction Noyes-Field-Koros Model
The Back-Switch
6Ce4+ + MA + 2H2O Ce3+ + HCOOH + 2CO2 + 6H (9)
4Ce4+ + BMA + 2H2O Ce3+ + Br- + HCO2H + 2CO2 + 5H+ (10)
Early: Mostly MA present, no bromide is formed.
Later: BMA is present, bromide is formed. Process (B) shuts down when [HBrO2] drops below [HBrO2]crit.
Now we know why solutions reacting by (B) will turn themselves into solutions reacting by (A).

22. Belousov-Zhabotinsky Reaction NFK Model Modifications: COx

23. Lengyel Reaction Iodination of Malonic Acid with Chlorite and
in the presence of Iodide
I2 + MA IMA + HI (L3) slow
r3 = -d[I2]/dt = 410-3 [MA] [I2] / {1 [l2]} (L3’)
Iodine consumption rate via reaction L3
Involves MA enolization and subsequent rxn with iodine
Batch Oscillation in the Reaction of Chlorine Dioxide with Iodine and Malonic Acid.
Lengyel, I.; Rabai, G.; Epstein, I. R. J. Am. Chem. Soc. 1990, 112,

24. Lengyel Reaction Iodination of Malonic Acid with Chlorite and
in the presence of Iodide
I2 + MA IMA + HI (L3) slow
ClO2 + I I2 + ClO (L4)
ClO I H I2 + Cl H2O (L5)
r4 = 6.3103 [ClO2] [I-] (4’)
r5 = 4.6102 [ClO2-] [I-][H+] 10-3 [ClO2-][l2]/[I-] (5’)
r5 = 4.6102 [ClO2-] [I-][H+] 10-3 [ClO2-][l2][I-]/(u+[I-]2) (5”)
u = 10-13
Iodine formation rates via reactions L4 & L5
This term reflects
self-inhibition by iodide
Avoid div.
by zero

25. Lengyel Reaction Mathematical Evaluation: Numerically.
Start with initial conditions and evolve concentrations over small times.
Mathematical Evaluation: Analytically.
Keep constant: [MA], [I2], [ClO2]
Remaining variables: [I-] = X; [ClO2-] = Y; [ClO2] = Z.
Taube's Influence on the Design of Oscillating Reactions – CIO2 Radical-Driven CIO2-Anion Iodine Oscillator and Turing
Structures. Irving R. Epstein, Kenneth Kustin, and Istvan Lengyel, 1997.

26. Lengyel Reaction
Taube's Influence on the Design of Oscillating Reactions – CIO2 Radical-Driven CIO2-Anion Iodine Oscillator and Turing
Structures. Irving R. Epstein, Kenneth Kustin, and Istvan Lengyel, 1997.

27. Excel Simulation programmed by Dr. Montgomery-Smith
Lengyel Reaction
Excel Simulation programmed by Dr. Montgomery-Smith
Series 1: X; Series 2: Y