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Summary Article: Polanyi, Michael (1891-1976)
from The Hutchinson Dictionary of Scientific Biography

Place: Hungary

Subject: biography, chemistry

Hungarian-born British physical chemist, particularly noted for his contributions to reaction kinetics. In later life he diverted his attention to social philosophy, in which he became equally renowned. Throughout his career he voiced his firm belief in the right of the scientist to seek the truth unhampered by external constraints.

Polanyi was born in Budapest on 12 March 1891. He entered the University of Budapest in 1909 to study medicine, but after graduation went to the Technische Hochschule at Karlsruhe as a student of chemistry under Georg Bredig. After service as a medical officer during World War I, he returned briefly to Karlsruhe before joining the Kaiser Wilhelm Institute of Fibre Chemistry in Berlin. In 1923, at the invitation of Fritz Haber, Polanyi moved to the Institute for Physical and Electro-Chemistry. But he became increasingly disturbed by the influence of the Nazi Party, especially its dismissal of Jewish scientists, and in 1933 he accepted the chair of physical chemistry at Manchester, England.

During the 1940s, Polanyi made the decision to concentrate on philosophy and in 1948 he transferred to the newly created chair of social studies at Manchester. On retiring from this position in 1958 he moved to Merton College, Oxford, as senior research fellow. He died in Northampton on 22 February 1976.

Polyani's early researches in chemical physics resulted in several papers on the adsorption of gases by solids. He introduced the idea of the existence of an attractive force between a solid surface and the atoms or molecules of a gas; he also suggested that the adsorbed surface is a multilayer and not subject to simple valency interactions. His other work of about that time extended the theory of Hermann Nernst (which stated that the entropy of a system approaches zero as the temperature decreases towards absolute zero). Polanyi showed that an increase in pressure must have the same effect, although in practice the highest attainable laboratory pressure is less effective than a very modest temperature increase.

At Berlin Polanyi's interest turned to X-ray analysis, using the newly developed rotating crystal method. He and his co-workers improved the technique and applied it to the determination of the structure of cellulose fibres. He also investigated the physical and mechanical properties of various materials; he grew crystals of metals and devised a special apparatus to measure their shear and rupture strengths.

Even as early as 1920 Polanyi recognized that the current theories of chemical reaction rates were simplifications of the truth. The collision theory postulated that only molecules with a certain critical energy would react. Working first under Haber and then at Manchester Polanyi extended this idea and produced theories of rates of association and dissociation based on the angular momenta of the colliding particles. Then quantum mechanics presented the kineticist with a powerful new tool. Reactions were considered in terms of the variation in potential energy of a system, which could be plotted as a function of the distance between reacting nuclei to produce a diagram somewhat resembling a contour map. The configuration of the components at the ‘mountain pass’ was defined as the activated complex, and the ‘height’ of the pass represented the activation energy.

Polanyi and Eyring investigated the reaction between a hydrogen atom and a hydrogen molecule:

H + H2(para) → H + H2(ortho)

and made the first reasonable accurate determination of its energy surface (ortho- and parahydrogen are isomers that differ only in the direction of spin of their nuclei).

Polanyi also played a part in solving a problem that had long been puzzling kineticists. It was known that in the hydrogen-iodine equilibrium:

H2 + I2 ⇌ 2HI

the rate of reaction is given by the equation:

d[HI]/dt = K[H2][I2]

where K is a constant. But in the apparently analagous reaction between hydrogen and bromine, experiment showed the reaction rate to be given by:

d[HBr]/dt = k[H2][Br2] 1/2/m + [HBr]/[Br2]

where k and m are constants. This expression implies that the velocity of the reaction is inhibited by the presence of the product HBr. Polanyi and others proposed a chain mechanism for the reaction:

In his new philosophical role at Manchester, Polanyi was active in the Society for Freedom in Science. He advocated that scientific research need not necessarily have a pre-stated function and expressed the belief that a commitment to the discovery of truth is the prime reason for being a scientist. His principal work was an investigation of the processes by which high-level skills such as craftsmanship and connoisseurship are acquired and the means by which such skills are shared and extended. His move to Oxford in 1958 coincided with the publication of his book Personal Knowledge, of which he said ‘The principal purpose of this book is to achieve a frame of mind in which I may firmly hold what I believe to be true, even though I know it may conceivably be false’.

© RM, 2018. All rights reserved.

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