viernes, 7 de enero de 2011

nobel 3ra publicacion. CRF. alfonso herrera. 3er parcial

The Nobel Prize in Chemistry 1901

JacobusHenricus van 't Hoff (1852-1911).

Jacobus H. van 'tHoffJacobusHenricus van 't Hoff was born in Rotterdam, The Netherlands, on August 30, 1852. He was the third child in a family of seven children of JacobusHenricusvan 't Hoff, a physician, and AlidaJacobaKolff.

In 1869 he entered the Polytechnic School at Delft and obtained his technology diploma in 1871. His decision to follow a purely scientific career, however, came soon afterwards during vacation-work at a sugar factory when he anticipated for himself a dreary profession as a technologist. After having spent a year at Leiden, mainly for mathematics, he went to Bonn to work with A.F. Kekulé from autumn 1872 to spring 1873; this period was followed by another in Paris with A. Wurtz, when he attended a large part of the curriculum for 1873-1874. He returned to Holland in 1874 and obtained his doctor's degree that same year under E. Mulder in Utrecht.

In 1876 he became lecturer at the Veterinary College at Utrecht, but left this post for a similar position at the University of Amsterdam the following year. In 1878 came his appointment as Professor of Chemistry, Mineralogy, and Geology at the same university. After having occupied this chair for 18 years he accepted an invitation to go to Berlin as Honorary Professor, connected with a membership of the Royal Prussian Academy of Sciences. The principal reason for this change was the fact that he was overburdened with obligations to give elementary lectures and to examine large numbers of students, including even those for medical propaedeutics, leaving him with too little time to do his own research work. He was an ardent advocate for the creation of a special class of scientific workers. At his new post he remained till the end of his life.

van 't Hoff has acquired fame particularly by his epoch-making publications. His doctor's thesis (1874) was entitled Bijdrage tot de Kennis van Cyaanazijnzuren en Malonzuur (Contribution to the knowledge of cyanoacetic acids and malonic acid). Of far greater weight, however, was his publication which appeared several months before: Voorstel tot Uitbreiding der Tegenwoordige in de ScheikundegebruikteStructuurformules in de Ruimte, etc. (Proposal for the development of 3-dimensional chemical structural formulae). This small pamphlet, consisting of twelve pages text and one page diagrams, gave the impetus to the development of stereochemistry. The concept of the "asymmetrical carbon atom", dealt with in this publication, supplied an explanation of the occurrence of numerous isomers, inexplicable by means of the then current structural formulae. At the same time he pointed out the existence ofrelationship between optical activity and the presence of an asymmetrical carbon atom.

His revolutionary ideas, however, only found acceptance after the publication, in 1875, of his Chimiedansl'Espace; especially when two years later the German translation appeared, with an introduction by J. Wislicenus. (The English translation: Chemistry in Space did not appear until 1891.) In his Dix Annéesdansl'Histoired'uneThéorie (Ten years in the history of a theory) he drew attention to the fact that J.A. Le Bel had independently arrived at the same ideas, though in a more abstract form.

In 1884 his book Études de Dynamiquechimique (Studies in dynamic chemistry) appeared, in which he entered for the first time the field of physical chemistry. Of great importance was his development of the general thermodynamic relationship between the heat of conversion and the displacement of the equilibrium as a result of temperature variation. At constant volume, the equilibrium in a system will tend to shift in such a direction as to oppose the temperature change which is imposed upon the system. Thus, lowering the temperature results in heat development while increasing the temperature results in heat absorption. This principle of mobile equilibrium was subsequently (1885) put in a general form by Le Chatelier, who extended the principle to include compensation, by change of volume, for imposed pressure changes - it is now known as the van 't Hoff-Le Chatelier principle.

The following year, in 1885, followed L'Équilibrechimiquedans les Systèmesgazeuxoudissous à I'Étatdilué (Chemical equilibria in gaseous systems or strongly diluted solutions), which dealt with this theory of dilute solutions. Here he demonstrated that the "osmotic pressure" in solutions which are sufficiently dilute is proportionate to the concentration and the absolute temperature so that this pressure can be represented by a formula which only deviates from the formula for gas pressure by a coefficient i. He also determined the value of i by various methods, for example by means of the vapour pressure and Raoult's results on the lowering of the freezing point. Thus van 't Hoff was able to prove that thermodynamic laws are not only valid for gases, but also for dilute solutions. His pressure laws, given general validity by the electrolytic dissociation theory of Arrhenius (1884-1887) - the first foreigner who came to work with him in Amsterdam (1888) - are considered the most comprehensive and important in the realm of natural sciences.

During his Berlin period he was from 1896 to 1905 continuously engaged on the problem of the origin of oceanic deposits, with special reference to those formed at Stassfurt. In this extensive work he was especially assisted by W. Meyerhoffer, who had previously worked with him in Amsterdam for a number of years. He was probably the first to apply small-scale results, obtained in the laboratory, to phenomena occurring on a large scale in Nature. The results of this ambitious investigation, mostly published in the Proceedings of the Prussian Academy of Sciences, were summarized by him in a two-volumes work ZurBildungozeanischerSalzablagerungen, 1905-1909.

van 't Hoff greatly valued the power of imagination in scientific work, as is apparent from his inaugural address on taking up his professorship in Amsterdam: Verbeeldingskracht in de Wetenschap (The power of imagination in Science), in which, after a rather elaborate study of biographies, he arrived at the conclusion that the most prominent scientists have possessed this quality in a high degree. Wilhelm Ostwald, who together with him established the ZeitschriftfürphysikalischeChemie in Leipzig, and can be regarded as founders of physical chemistry.

Of the numerous distinctions he himself mentioned the award of the first Nobel Prize in Chemistry (1901) to him as the culmination-point of his career. In 1885 he was appointed member of the Royal Netherlands Academy of Sciences, after his nomination had been withheld in 1880 because of an insufficient number of votes - a proof that his ideas initially found little acceptance in his own country. Among his other distinctions were the honorary doctorates of Harvard and Yale (1901), Victoria University, Manchester(1903), Heidelberg (1908); the Davy Medal of the Royal Society (1893), Helmholtz Medal of the Prussian Academy of Sciences (1911); he was also appointed Chevalier de la Legion d'Honneur (1894), Senator der Kaiser-Wilhelm-Gesellschaft (1911). He was also member or honorary member of the Chemical Society, London (1898), Royal Academy of Sciences, Gottingen (1892), American Chemical Society (1898), Académie des Sciences, Paris (1905).

van 't Hoff was a lover of nature; as a student in Leyden he frequently took part in the botanical excursions, and later in Bonn he fully enjoyed the mountains in the vicinity, taking long walks in company or alone. His quite detailed description of his journey to the United States, resulting from an invitation to lecture at Chicago University, amply shows his love of travel. His receptiveness for philosophy and his predilection for poetry were already apparent in his early school years - Lord Byron was his idol.In 1878 he married Johanna FrancinaMees. They had two daughters, Johanna Francina (b. 1880) and AleidaJacoba (b. 1882) and two sons, JacobusHendricus (b. 1883) and Govert Jacob (b. 1889).

Alfonso Herrera

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