Van't Hoff, Jacobus Hendricus
van't Hoff, Jacobus Hendricus
COFOUNDER OF MODERN STEREOCHEMISTRY AND PHYSICAL CHEMISTRY
1852–1911
Jacobus Hendricus van't Hoff, born in Rotterdam, Netherlands, was in his youth, along with the French chemist Joseph Achille Le Bel, the cofounder of modern stereochemistry. He then became one of the fathers of modern physical chemistry. In 1901 he was awarded the first Nobel Prize in chemistry for his work on chemical dynamics and the osmotic pressure in solutions.
As is the case with many creative minds, van't Hoff's career initially encountered many roadblocks, mostly related to the ignorance of the scientific establishment. Unemployed for two years after receiving his doctorate, he eventually took a teaching job in physics at the veterinary school in Utrecht. Success finally came in 1877 when the newly founded University of Amsterdam offered him a lectureship; the next year he became a professor of chemistry at the same institute. Although his international reputation led to the formation of a new chemical laboratory at the Amsterdam school, which was completed in 1891, he moved to Berlin in 1896 as both a university professor and member of the prestigious Prussian Academy of Science.
Shortly before he submitted an only average doctoral thesis in synthetic organic chemistry to the University of Utrecht, the twenty-two-year-old van't Hoff had printed and distributed a twelve-page pamphlet at his own expense that, although ignored for many years, essentially outlined the foundation of modern stereochemistry. Inspired by the earlier ideas of the German chemist Johannes Wislicenus to extend chemical structure theory from constitutional chemical formulas to representations in three-dimensional space, van't Hoff suggested a structural distinction between optical isomers that had been represented up until that time by the same formula. By screening known substances for optical activity (i.e., the rotation of the plane of polarized light), he found that all their constitutional formulas contained at least one carbon atom that combined with four different atomic groups. If the latter were placed at the corners of a tetrahedron in three-dimensional space, with the carbon atom at its center, there were exactly two possible tetrahedra with asymmetric carbon atoms, each being the mirror image of the other, that could account for the pairs of optical isomers. This structural theory was further supported by his observation that for every known chemical transformation where the optical activity of a reactant disappeared, there was no more asymmetric carbon atom in the structural representation of the reaction product. Independently and virtually simultaneously, Le Bel arrived at the same theory in Paris.
Due to his early interest in philosophy, particularly the ideas of French philosopher Auguste Comte, van't Hoff's chemical research strove for general and theoretical insight into chemistry and thus gradually shifted from organic to physical chemistry. In 1884 he published his well-known Études de dynamique chimique (Studies in chemical dynamics); it contained many important ideas on chemical kinetics and thermodynamics that confirm van't Hoff's status as a true pioneer in the field. Based on numerous measurements of organic reaction rates, he classified chemical reactions according to different orders and molecularities and formulated the temperature dependence of reaction rates, now known as the "Arrhenius equation." Following through on earlier ideas, he interpreted chemical equilibria as dynamic states where backward and forward reaction rates were equal, which he represented by a double arrow. He further formulated the temperature dependence of the equilibrium constant, known as the "van't Hoff isochore," and suggested what later came to be known as "Le Chatelier's principle." Most important, he established the foundation of chemical thermodynamics by expressing the relationship between what is now called the free energy of a reaction and its equilibrium constant.
During the late 1880s van't Hoff turned the seemingly exotic phenomenon of osmotic pressure into a crucial part of the new physical chemistry of solutions. He discovered that the osmotic pressure π increased with the concentration of the solute, c = n /V, and the absolute temperature T according to the equation
which is equivalent to the ideal gas law if one replaces the osmotic pressure π, with the gas pressure, p :
with R being the gas constant in both cases. The surprising correspondence between the two suggested that the osmotic pressure depended only on the number of solute molecules and not their chemical nature, like other so-called colligative properties such as vapor pressure lowering and freezing point depression. Van't Hoff did not simply advance all these phenomena on a common thermodynamic basis; he also successfully explained apparent anomalies with the Arrhenius theory of electrolytic dissociation.
In his later years, van't Hoff applied chemical thermodynamics to the formation of marine salt deposits, which made him one of the pioneers in the science of petrology.
see also Thermodynamics.
Joachim Schummer
Bibliography
Hornix, Willem J., and Mannaerts, S. H. W. M., eds. (2001). Van't Hoff and the Emergence of Chemical Thermodynamics: Centenary of the First Nobel Prize for Chemistry, 1901–2001. Delft, Netherlands: DUP Science.
Snelders, H. A. M. (1976). "Van't Hoff, Jacobus Hendricus." In Dictionary of Scientific Biography, Vol. XIII, ed. Charles C. Gillispie. New York: Scribner.
Jacobus Hendricus Van't Hoff
Jacobus Hendricus Van't Hoff
The Dutch physical chemist Jacobus Hendricus Van't Hoff (1852-1911) pioneered in the development of stereochemistry.
Jacobus Hendricus Van't Hoff was born in Rotterdam on Aug. 30, 1852. He developed an early interest in science, and in spite of the opposition of his father, who was a medical doctor, he studied chemistry at a polytechnic school and then at the University of Leiden. From the Netherlands he journeyed to Germany and then to Paris for further study, finishing his doctorate at the University of Utrecht in 1874.
Just prior to the awarding of the degree, however, Van't Hoff published a surprising scientific paper on the optical activity of certain organic compounds. This phenomenon (stereochemistry) of organic compounds can be described briefly by reference to the two forms of tartaric acid. They are the same in chemical formula, but in solution one form rotates a beam of polarized light to the left, and the other rotates it to the right. Pasteur had observed this phenomenon years earlier and suggested that the compound was actually made up of crystals which were mirror images of each other, but this explanation did not seem to have any application to compounds in solution. Van't Hoff's contribution was to describe asymmetry in molecules, not in crystals, and he showed how this was possible if one considers the carbon atom as having four linkages which do not lie in a plane but are directed toward the four angles of a tetrahedon. In this way, the carbon atom achieves a three-dimensional form, and the attachment to it of different types of chemical groupings establishes asymmetric molecules and compounds.
Van't Hoff became a lecturer in chemistry at the Veterinary College in Utrecht. From there he went to the University of Amsterdam, and he ended his career at the University of Berlin, where he taught and engaged in research from 1896 to 1911. In 1901 he received the first Nobel Prize in chemistry, which was awarded him for his work with solutions. His achievements in this field were made during the second part of his scientific career, when he was a physical chemist. In the first part of his career, it may be said that he was an organic chemist. The results of his research in chemical thermodynamics were published in Studies in Chemical Dynamics (1884).
Van't Hoff's work on the theory of solutions formed the major part of his creative research in physical chemistry. He was able to show that, in very dilute solutions, the laws of gases may be applied to the molecules. Before his work, chemists had possessed only vague ideas about molecular behavior in solutions; Van't Hoff's research cleared up many questions. Van't Hoff had a generalizing and speculative mind which gave him insights into the newly developing field of physical chemistry. He died on March 1, 1911.
Further Reading
Ernst Cohen, who wrote the definitive biography of Van't Hoff in German, contributed a biographical sketch of the scientist in Eduard Farber, ed., Great Chemists (1961). Van't Hoff is mentioned in Isaac Asimov's survey, A Short History of Chemistry (1965). □