Vant Hoff, Jacobus Hendricus

Born Aug. 30, 1852, in Rotterdam; died Mar. 1, 1911, in Berlin. Dutch chemist; one of the founders of modern physical chemistry and stereochemistry. Graduated from the Polytechnic in Delft in 1871 and then worked in Leiden and Bonn under A. Kekulé and A. Wurtz.

In 1874, van’t Hoff defended his doctoral dissertation at the University of Utrecht. In 1876 he became an assistant professor at the Veterinary School in Utrecht and in 1878 a professor of chemistry, mineralogy, and geology at the University of Amsterdam. Beginning in 1896 he was a professor at the University of Berlin and a member of the Prussian Academy of Sciences. From 1895 he was also a foreign corresponding member of the St. Petersburg Academy of Sciences.

In 1874-75, van’t Hoff first set forth the theory of the spatial distribution of atoms in the molecules of organic compounds; this theory forms the basis of modern stereochemistry. He created or considerably broadened the fields of chemical kinetics, the thermodynamics of chemical reactions, the theory of dilute solutions, and the teachings on equilibriums in aqueous-saline systems. Basing his work on the research of N. A. Menshutkin, van’t Hoff established that the speed of reaction when a change occurs within only one molecule is proportional to the concentration of the reacting substance, whereas when two or three molecules take part in the reaction, the speed is proportional to the product of their concentrations. Van’t Hoff was the author of one of the fundamental equations of chemical thermodynamics, which expresses the dependence of the equilibrium constant on the temperature of the reaction and shows that this dependence is determined by the thermal effect of the reaction. He derived a formula that expresses the equilibrium constant in terms of the change in free energy (Gibbs free energy). The law of active masses for a chemical equilibrium received thermodynamic justification in the same way.

Works by van’t Hoff devoted to dilute solutions appeared in the period from 1885 to 1889. Van’t Hoff tied together observations pertaining to osmotic pressure, vapor pressure above a solution, and the dependence of the freezing and boiling points of solutions on their concentration. He established that the osmotic pressure is equal to the pressure that would be produced by a dissolved substance if it were in a gaseous state at the same temperature in a volume equal to the volume of the solution. It was found, however, that electrolytes produce a higher osmotic pressure than might be expected on the basis of their molecular weight. In order to calculate this pressure, van’t Hoff introduced the empirical coefficient / into the gas formulas. Subsequently, S. Arrhe-nius came to the conclusion that the coefficient i indicates the degree of dissociation of the dissolved substance. In 1890, van’t Hoff extended his concepts about solutions to solid bodies as well, thereby introducing a new concept— that of solid solutions. Almost simultaneously with the works of dilute solutions, van’t Hoff, together with his students, began a number of studies on saturated saline solutions. The very extensive experiments had as their goal the explanation of the conditions of formation and use of the Stassfurt salt deposits.

The principles established by van’t Hoff, his experimental methods of research, and his application of analytical, thermodynamic, and geometric principles played a large role in the further development of chemistry. Van’t Hoff won the Nobel Prize in 1901.