Nernst, Walther Hermann (1864–1941)
NERNST, WALTHER HERMANN (1864–1941)
Walther Hermann Nernst was born in Briesen on June 25, 1864, into a prominent Prussian family. The line of his ancestors can be traced back to the era of the first Prussian king in the seventeenth century. His most famous ancestor is Hermann Nernst, who received an award for conveying the news to the king's family about the Germans victory against Napoleon in the Battle of Waterloo. Nernst lost his mother, Ottilie Nerger, very early. His father, Gustav Nernst, was a district judge. Nernst was a very impulsive person and known for his impatience. He died of a heart attack in his country house in Zibelle on November 18, 1941.
When Nernst attended secondary school, his chemistry teacher awakened in him a passion for chemistry. This left a deep impression on the young pupil, who started early to do his own chemistry experiments at home, in the cellar. Nernst often changed universities during his study of physics, as he wanted to take part in selected lectures by the most influential comtemporary scientists. First he visited the physics lectures of Heinrich Friedrich Weber in Zurich in 1883 and then he went to Berlin for a semester to take thermodynamics lessons from Hermann von Helmholtz, the most famous German physicist at that time. After another semester in Zurich, Nernst studied for the fourth semester in Graz, where Ludwig Boltzmann founded the statistical interpretation of thermodynamics. Nerst, finished his education there and started his Ph.D. program in collaboration with Albert von Ettinghausen, one of Boltzmann's students. Nerst, finished his Ph.D. requirements in Wurzburg in 1887 under the supervision of Friedrich Whilhelm Georg Kohlrausch, who entered a completely new physical field with his research on the ionic conductance of liquids. Nernst adopted Boltzmann's atomistic view (or mechanical picture) of natural phenomena and combined it with the energetic view that he became familiar with during his collaboration with Wilhelm Ostwald in Leipzig. It was due to Svante Arrhenius that Nernst became highly interested in the new topic of ionic theory that was established by Ostwald. Fascinated by this topic, Nernst habilitated in Leipzig in 1889 on the electromotive activity of ions. He incorporated into this work Arrhenius' theory of dissociation and Jacobus Henricus van't Hoff's osmotic theory of solutions. Two years later Nernst became an assistant professor in physical chemistry at the University of Gottingen. In 1905 he was offered an appointment as the successor of Hans Landolt and started his work at the University of Berlin. In the same year he discovered the third law of thermodynamics during the time he was lecturing on the thermodynamical treatment of chemical processes. Nernst worked in many fields of physical chemistry—for example the osmotic theory of galvanic elements, the law of distribution, equilibrium at high temperatures and high pressures, specific heats at high and low temperatures, calorimetry, IR radiation, chain reactions, electrochemistry, and photochemistry.
Of fundamental importance to Nernst's discovery of the Third Law of Thermodynamics is Nicholas Leonard Sadi Carnot's work in the middle of the nineteenth century establishing thermodynamics by combining the laws of motion with the concept of action. At the same time Helmholtz found that the principle of energy conservation is also valid for thermal energy and established together with Robert Julius Mayer and James Joule the first law of thermodynamics. A short time later Rudolf Clausius and Carnot introduced the concept of entropy and established the second law of thermodynamics. The chemical affinity—the extent to which a compound is reactive with a given reagent—was known of since attempts of alchemists to produce gold in the Middle Ages. The importance of the concept of chemical affinity was first recognized by van't Hoff. He showed that it was possible to measure the chemical affinity via free energy. Helmholtz and Josiah Gibbs independently established an exact mathematical relationship between the total energy (the energy content of a system) and the free energy (the capacity of a system to perform work). According to Marcellin Pierre Berthelot the total and the free energy should be the same during the electrochemical processes in the galvanic cells Nernst was investigating. Nernst's experiments showed that this statement was not exactly valid for moderate temperatures, and the deviation became larger as the temperature was increased. Therefore he assumed that both energies should be equal at zero value of temperature. Finally, he got the idea that the difference between these two energies asymptotically approaches zero as the absolute temperature approaches zero. This is the first formulation of the new law. Nernst was led to this law, which he and other scientists spent a long time investigating, while he was searching for mathematical criteria for the description of chemical equilibrium and the spontaneity of chemical reactions. That why some chemical reactions are spontaneous while others are not was already known a century before Nernst's own discovery. Since 1900 it was known that a thermodynamical calculation of the chemical equilibrium could not be performed using only the thermal data of the current thermodynamics because the integrated form of the Gibbs-Helmholtz Equation—which allowed calculation of the maximum yield of work during a thermodynamical process—contained an undetermined integration constant.
Nernst's contribution to the solution of this problem was to give this undetermined constant a new interpretation. This new interpretation, however, required an additional assumption for the description of the free energy exchange in the vicinity of the absolute zero value of temperature. He recognized that the work function for the state transition of a system could not be calculated by means of energy differences. Rather, derivatives of the energy and the free energy with respect to temperature were necessary. Furthermore, Nernst assumed that the entropy approaches a constant value provided the absolute temperature approaches zero.
After Nernst's publication of his Heat Theoremall resources of the Institute for Physical Chemistry at the University of Berlin were dedicated to its experiments. No experimental result was found to contradict Nernst's heat theorem. Its general validity, which was established by experiments in many subfields of physical chemistry, justified its inclusion among the laws of thermodynamics. This law was regarded by Arnold Sommerfeld as "the most ingenious extension the classical thermodynamics ever experienced in the twentieth century." Expressing Nernst's heat theorem in terms of entropy, this law means that the entropy difference between different states of a system tends to zero as the temperature reaches absolute zero. It can also be expressed as the law of unattainability of absolute zero temperature. Franz Eugen Simon provided Nernst's heat theorem a more elegant theoretical foundation and reformulated it by stating that the entropy differences disappear between all those states of a system that are in internal thermodynamic equilibrium. Very soon after he set forth the third law of thermodynamics, Nernst showed the importance of his discovery by calculating the chemical equilibrium using thermal data only. Nernst was awarded the Nobel Prize in chemistry in 1920 as recognition of his work in thermochemistry.
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