le Châtelier, Henri Louis (1850-1936) was a French physical chemist, best known for the principle named after him which states that if any constraint is applied to a system in chemical equilibrium, the system tends to adjust itself to counteract or oppose the constraint. Le Châtelier was born in Paris on 8 October 1850, the son of France' s Inspector-General of Mines. He was educated at the Collège Rollin in Paris and went to study science and engineering at the Ecole Polytechnique, although his studies were interrupted by the Franco-Prussian War (1870-1871). He graduated in 1875 then, after working for two years as a mining engineer, he took up an appointment as Professor of Chemistry at the Ecole des Mines in 1877. In 1898 he moved to the Collège de France as Professor of Mineral Chemistry, before finally settling at the Sorbonne in 1908 as Professor of Chemistry in succession to Henri Moissan (1852-1907). He worked for the Ministry of Armaments during World War I and retired in 1919. He died at Miribel-les-Echelles, Isère, on 17 September 1936. Le Châtelier's first major contribution was to temperature measurement, a subject that followed naturally from his high-temperature studies of metals, alloys, glass, cement and ceramics. In 1887 he devised a platinum/rhodium thermocouple for measuring high temperatures by making use of the Seebeck effect (the generation of a current in a circuit made up of two dissimilar metals with the junctions at different temperatures; the magnitude of the current is proportional to the difference in temperature). Le Châtelier also made an optical pyrometer which measures temperature by comparing the light emitted by a high- temperature object with a standard light source. This work involving flames and thermometry led him to thermodynamics, and in 1884 le Châtelier put forward the first version of his principle, in which he stated that a change in pressure on an equilibrium system results in a movement of the equilibrium in the direction that opposes the pressure change. By 1888 he had generalized the principle as the Loi de stabilité de l'équilibre chimique and applied it to any change that affects chemical equilibrium. In its general form le Châtelier' s principle is all-embracing, and includes the law of mass action, as formulated by Cato Guldberg (1836-1902) and Peter Waage (1833- 1900) in 1864. It is particularly relevant in predicting the effects of changes in temperature and pressure on chemical reactions: for example, it predicts that a rise in temperature or an increase in pressure should facilitate or accelerate a reaction that is reluctant to take place at normal temperatures and pressures. Industrial chemists, such as Fritz Haber and his process for synthesizing ammonia, were soon to make good use of the principle. It also agreed with the new thermodynamics being worked out in the United States by Josiah Willard Gibbs. Le Châtelier was largely responsible for making Gibbs' researches known in Europe, translating his papers into French and performing experiments to test the phase rule. He also wrote extensively about labour relations and efficiency in industry. In 1895 he put forward the idea of the oxyacetylene torch for cutting and welding steel. Author not available, le Chatelier, Henri Louis (1850-1936). , The Hutchinson Dictionary of Scientific Biography, 01-01-1998. |