In 1921, the first oscillating reaction was discovered by W. C. Bray of the University of California at Berkeley. This reaction was the decomposition of H₂O₂ in O₂ and H₂O with IO₃^-. The study of this reaction was made by Bray and one of his students Hermann Liebhafsky.

 The best known oscillating reaction was discovered by the Russian biochemist Boris Pavlovich Belousov in 1950.

During his research on the Krebs cycle in 1950, he discovered that a solution of citric acid in water (with acidified bromate as oxidant and yellow ceric ions as catalyst) turned colorless and then back to yellow for an hour while bubbling carbon dioxide.

In 1951, Belousov wrote a paper describing this reaction, but his article was rejected because his results seemed to be contrary to the laws of thermodynamics. At that time, chemists believed that oscillations in closed homogeneous systems were impossible because that would imply that the reaction did not achieve the thermodynamic equilibrium smoothly. Six years later, Belousov submitted an exhaustive manuscript with detailed evidence of his conclusions to a different journal.

In 1961, a young graduate student in biophysics at Moscow State University called Anatol M. Zhabotinsky (working under S.E. Schnoll) rediscovered the oscillating reaction replacing citric acid by malonic acid and observing oscillations with larger amplitudes.

It was not until 1968 in a Symposium on Biological and Biochemical Oscillators in Prague that western specialists decided to research on oscillating reactions.

 In 1973 two teachers, Briggs and Rausher added CH2(COOH)₂ and Mn²⁺ to the Bray-Liebhafsky reaction; the oscillations were accentuated and their periods reduced to a few seconds. 

3.4-The second law problem

 The power of the Second Law lies in its ability to predict the direction of spontaneous change from the simple condition that dG<0. dG is the free energy of the system and it is equal to dH (enthalpy change) minus TdS, where T is temperature and dS is the total entropy variation of an isolated system or of the universe. dG = dH - TdS dG<0. These detractors concluded that an oscillating reaction would require the free energy of the system to oscillate as the reactants were converted into products and then back to reactants, and would therefore contradict the Second Law. 

3.5-Ilya Prigogine's contribution

 At the beginning of the 1930's, Ilya Prigogine and other scientists tried to apply classical thermodynamic results to far from equilibrium systems, but they quickly realized that a new theory was required to explain accurately these strange systems. Prigogine, specialized on chemical systems, pointing out that a system can decrease its entropy, as long as the total entropy exchange in the universe is positive. Ilya Prigogine was awarded with the Nobel Prize in Chemistry in 1977.

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