Richard Macy Noyes pioneer in chemical kinetics

Richard Macy Noyes – pioneer in chemical kinetics

Article on Richard Macy Noyes

Biography & Contributions

Richard Macy Noyes was an American physical chemist born on April 06, 1919 – died on November 25, 1997. Noyes directed his scientific work almost entirely toward understanding the details of how chemical reactions occur, making seminal contributions in isotopic-exchange processes, the theory of molecular diffusion in solution, and treatment of complex kinetics and reaction mechanisms. His research area was focused on the kinetic studies of oscillating reactions. In 1976, he was able to identify the reaction mechanism of the Bray-Liebhafsky reaction.

Noyes also worked on Cis-trans isomerization and iodine-exchange kinetics of diiodoethylene. He made some of the very first radioisotope exchange-kinetics measurements using very small samples of unknown isotopes of iodine obtained from a Berkeley cyclotron.

Belousov-Zhabotinsky reaction

A Belousov-Zhabotinsky reaction, or BZ reaction, is one of a class of reactions that serve as a classical example of non-equilibrium thermodynamics, resulting in the establishment of a nonlinear chemical oscillator. Boris Belousov was the discoverer of this phenomenon. He noted, in the 1950s, that in a mix of potassium bromate, cerium(IV) sulfate, malonic acid and citric acid in dilute sulfuric acid, the ratio of concentration of the cerium(IV) and cerium(III) ions oscillated, causing the colour of the solution to oscillate between a yellow solution and a colorless solution. This is due to the cerium (IV) ions being reduced by malonic acid to cerium (III) ions, which are then oxidized back to cerium (IV) ions by bromate (V) ions.

Oscillating Chemical Reactions

Oscillating reactions are among the most fascinating of chemical reactions. In one type of reaction, a mixture of chemicals goes through a sequence of color changes, and this sequence repeats periodically. The oscillations in an oscillating chemical reaction are driven by the decrease in free energy of the mixture. This decrease is what drives all chemical reactions, but not all chemical reactions exhibit oscillations.

The reaction mechanisms of all known chemical oscillators have at least three common features. First, while the oscillations occur, the chemical mixture is far from equilibrium, and an energy releasing reaction occurs whose energy drives the oscillating "sideshow." Second, the energy-releasing reaction can follow at least two different pathways, and the reaction periodically switches from one pathway to another. Third, one of these pathways produces a certain intermediate, while another pathway consumes it, and the concentration of this intermediate functions as a "trigger" for the switching from one pathway to the other.

When the concentration of the intermediate is low, the reaction follows the producing pathway, leading to a relatively high concentration of the intermediate. When the intermediate's concentration is high, the reaction switches to the consuming pathway, and the concentration of the intermediate decreases. Eventually the reaction reverts to the producing pathway. The reaction repeatedly switches from one pathway to the other.

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