Behaviour of a bz oscillating system at low temperatures

29 July 1983

CHEMICAL PHYSICS LETTERS

Volume 99, number 2

BEHAVIOUR OF A BZ OSCILLATING SYSTEM AT LOW TEMPERATURES AK

DUTT and R.S. BANERJEE

~cparlnlmt

Kcccived

of ChemisrQ*. university College of Science, 92. A-P-C_ Road, Chlcutt~-7~0009,

4 t\pril 1953

Tbc BZ oscillating rwction has been studied at low temperatures period itself shotted sotne sort of periodicity.

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Fig. l_ BZ rwction of @ic acid-i;BrOa-HzSO;,-fcrroin [H,SO,] = 1.06-l 51, [ferroin] J 0.0005 hi.

and it was noted that strangely enough the oscillation

Gallic acid was used as the organic substrate in our system. To a weighed amount of garlic acid, H,SO, and ferroin were added and finally a requisite quantity of bromate solution in H2SOG was added. The reaction was stirred at a more or less fixed rate with the help of

The Belousov-Zhabotinskii oscillating reaction [I -41 is a well-studied one_ In connection with our study of the system at different temperatures in order to determine the kinetic paramters. we noted some peculiarities at low temperatures_

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system at 18S“C [gallic acid] = 0.036 hl, [KBrOa] = 0.1026 M.

0 009-2614/S3/0000-0000/S

03.00

0 1983 North-Holland

29 July 1983

CHEWCAL PHYSICS LETTERS

Volume 99. number 2

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Fig. 2. BZ reaction of gallic acid-liBr03-HzS04-ferroin system at different temperatures. [gllic acid] = 0.037 hl, [KBrO~] = 0.1026 hi, (H2S04] = 1.064 hl, [ferroin] = 0.0005 hl. Set I, 22_5”C,set iI,28_s”C, set III, 38.5-C; set IV, 45S°C.

a tnagnetic stirrer and the time period of oscillation was recorded visually. No reactant was added later. As the colour change (red to green) was sharp and excellent and the oscillations continued for some time, visual observation was quite satisfactory_ The reaction was studied at different temperatures, the range being 2955-3 18.5 K. The oscillation periods were then plotted against time at different temperatures as has been presented in figs. 1 and 2. The composition of the reaction mixture has also been shown in figs. 1 and 2, In sets II, III and IV of fig. 2 in the temperature range 301 S-318.5 K, the oscillation periods increased in a more or less regular way with decrease in temperature and this range was utilised to determine the activation parameters like energy of activation and entropy of activation. The results have been reported elsewhere [51The observations at low temperatures (291.5 and 295.5 K) as shown in the plots in figs. 1 and 2 (set I) appear to be peculiar. As the system used is thermo-

dynamically closed one should normally expect that the oscillations will be damped and the oscillation period will increase with time. During the early part of the reaction, however, the system may show sustained oscillation and the oscillation period may remain more or less constant. In fact the oscillation period increased with time at higher temperatures, i.e. 301-5, 311.5 and 318.5 K (sets II, III and IV in fig. 2). But at lower temperatures, i.e. at 29 1.5 and 295.5 K, the oscillation period increased gradually and then decreased gradually and this thing is repeated, i.e. some sort of periodicity of the oscillation period was observed. Though the observations are visual, the results do seem to be real as the changes are quite large. They are not just due to any natural scatter arising from any error in timing and repetitions give similar results. Moreover, the maximum temperature fluctuation during the experiment is F 1°C. So probably we are also not looking at artifacts from changes in tempera187

\kdume

99, number

2

CHEhfICAL

PHYSICS LEl-FERS

29 July 1983

ture. Although it is not possible at present to give any suitable explanation for the observations, they appear to be novel and quite interesting.

References

Sincere thanks are due to Professor R.M. Noyes, Chemistry department Oregon University, USA for his interest and encouragement.

12] A.hl. Zhabotinskii, Biofizika 9 (1964) 306. [ 3 ] R.J. Field, E. KZir6s and R.M. Noyes, J. Am. Chem.

[I] B.P. Belousov, Ref. Radiats. Med., 1958, hledgiz, hloscow, 145 (1959).

Sot. 94 (1972)

8649.

[4] R-Xl. Noyes. J. Am. Chem. Sot. 102 (1980) 4644. [S] AK Dutt and R-S. Banerjee, J. Chem. Ed., to be published.

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