Jacobus Henricus van 't Hoff

Jacobus Henricus van ' t Hoff ( born August 30, 1852 in Rotterdam, † March 1, 1911 in Berlin Steglitz b. ) Was a Dutch chemist and the first Nobel laureate in chemistry. Van ' t Hoff, the chirality of the carbon atom, the change in the physical properties depending on the number of particles in a solution, the kinetics of chemical reactions, and their temperature dependence explored.

Life

Van ' t Hoff's father worked as a general practitioner in Rotterdam.

In Rotterdam, the young Henricus attended a Latin -less " Hoogere Burger School ", corresponding to about a secondary school in Germany at that time. Since early youth, Van interested 't Hoff for chemistry. After his graduation in 1869, he studied at the Polytechnic Institute in Delft technology. After two years, he received his degree and permission to study. From 1871, he studied mathematics at the University of Leiden, then chemistry in 1872 with August Kekulé in Bonn and from 1873 with Charles Adolphe Wurtz in Paris. During his studies, Van interested 't Hoff for Philosophy ( Auguste Comte ), and poetry (Lord Byron, Heinrich Heine ). Even before completing his doctoral work surprised van ' t Hoff the experts with a short article for the optical rotatory power and the stereochemistry of carbon bonds. This item has not been respected by the professional colleagues.

In 1874 he received his doctoral degree at Utrecht University with a dissertation on cyanoacetic and malonic acid. There followed a period of fruitless applications for a university career. As a substitute teacher got van ' t Hoff in 1876 as an assistant at the Veterinary School of the University of Utrecht. 1876 ​​translated Wislicenus Johann van ' t Hoff's work on the asymmetric carbon atom into German. In Germany, the supreme importance of this Article was not initially appreciated.

However, in 1877 he was initially able to cross over as a lecturer for the Department of Chemistry of the University of Amsterdam and received in 1878 a professorship. There he developed a simple apparatus and dealt with the osmotic pressure. His published work in 1887, " The role of osmotic pressure in the analogy between solutions and gases " laid the foundations for the determination of molecular weight of substances in solution. Svante Arrhenius and Wilhelm Ostwald recognized the importance of van ' t Hoff's work. Based on its deliberations, the ionic theory of aqueous solutions ( dissociation) has been developed. Van ' t Hoff and Wilhelm Ostwald founded in 1887 the journal of physical chemistry.

Now he has received many honors. In 1896 he was appointed professor at the Prussian Academy of Sciences (or University of Berlin) in Berlin, where he worked until his death. He dealt here with the chemical equilibrium, with new methods for determining the molecular weight and the formation of salts from seawater and the order of deposits of different salt layers at certain temperatures and pressures.

He received in 1901 the first Nobel Prize in Chemistry for his discovery of the laws of chemical dynamics and osmotic pressure in solutions. For his experiments he used the artificial semipermeable membranes of the chemist Moritz Traube.

His grave is located in Berlin's Dahlem cemetery. The grave of honor of the city of Berlin is located in box 1

Scientific work

Even before the award of the doctoral degree, he published the first of his major contributions to organic chemistry. He explained, the phenomenon of the optical activity of the assumption in the optically active compounds of the chemical bonds between the carbon atoms and its four neighbors are spatially arranged such that the carbon atom at the center and the adjacent atoms are at the corners of a tetrahedron. The four bonds must all be different. This arrangement enables that the molecule can exist in the form of two enantiomers, that is a mirror image of the same construction. The same idea of the declaration of the optical activity was independent of it, the French chemist Joseph LeBel. In this respect, van 't Hoff developed the stereochemistry crucial.

Avogadro's law for solutions, dissociation

Van ' t Hoff developed the idea that the Avogadro's law could also apply to solutions. He found that the osmotic pressure of a solution is directly proportional to the amount of a substance dissolved in it. He concluded that for the same osmotic pressure and the same temperature and the same number of particles in each case would have to be solved. He then applied the equation of state (after Avogadro's law, Boyle 's law) for gases on solutions and was able to perform accurate molecular weight determinations.

Analogous considerations rendered van ' t Hoff on boiling point elevation and freezing point depression that François Marie Raoult was already purely empirical evidence. This allowed van ' t Hoff, molecular weight determinations and molecular sizes of solutes estimate. Variations in the previous theory, it was, however, when salts ( e.g., potassium chloride) in comparison to sucrose. The number of particles found for potassium chloride was twice as high as expected from the molecular mass. This finding supported the theory of Svante Arrhenius, who represented only by van ' t Hoff assisted his dissociation theory.

A more complex description of the theory of the electrolytic solution pressure, the electromotive force (EMF) of the galvanic element, has been developed by Walter Nernst. In this theory a similar description as the osmotic pressure was used.

Kinetics

Pioneering work made ​​van ' t Hoff in the field of kinetics with Etudes, Studies on the chemical dynamics ( 1896). Van ' t Hoff examined the reactions of chloroacetic acid and saponification of ethyl acetate with sodium hydroxide (both bimolecular reactions).

However, was preceded by investigations already by Ludwig Wilhelmy, Wilhelm Ostwald and Cato Maximilian Guldberg and Peter scale. Wilhelmy made ​​the first kinetic studies by the action of acid on sugar; The reaction rate was determined by a polarimeter. Later, Wilhelm Ostwald dealt with the chemical kinetics.

In the book, the temperature depending on reaction rates was examined. The solution of the differential equation of the temperature dependence is the van 't - Hoff'sches law. The by van ' t Hoff named van ' t Hoff - rule states that the rate of a chemical reaction doubles when the temperature increases by about ten degrees Celsius. The Van ' t Hoff factor brings the molar solubility behavior of a substance expressed. The Van 't Hoff - Reaktionsisobare specifies the derivative of the logarithm of the thermodynamic equilibrium constant on temperature at constant pressure.

Other services

Other fields were the thermodynamics (1884 defined van ' t Hoff affinity ) and oceanic salt deposits and geological deposits.

Writings

• Views about organic chemistry. 3 parts, Brunswick 1878-1881
• Etudes de dynamique Chimique. 1884; German: Studies on the chemical dynamics. 1898
• Lois de l' equilibre Chimique. 1885
• Lectures on formation and cleavage of double salts. Leipzig 1897
• Studies on the formation conditions of oceanic salt deposits, especially the Staßfurter salt deposits. Berlin 1897
• Lectures on theoretical and physical chemistry. Brunswick 1898-1900
• The laws of chemical equilibrium for dilute gaseous or dissolved state, Engelmann, Leipzig 1900, 2nd edition 1915 ( Van t'Hoff Act) First in French: Une propriété générale de la matière diluée in Kongl. Svenska vetenskapsakademiens handlingar, Volume 21, No. 17, 1886 and published in Archives Néerlandaises 1885.