Walther Nernst

German chemist and physicist

• Born: June 25, 1864; Briesen, Prussia (now in Germany)
• Died: November 18, 1941; Muskau, Germany

Walther Nernst was awarded the Nobel Prize in Chemistry in 1920 for developing the third law of thermodynamics. However, he is perhaps best known for his equation for the electrode potential of a voltaic cell.

Primary fields: Chemistry; physics

Specialties: Physical chemistry; thermodynamics

Early Life

Walther Hermann Nernst was born on June 25, 1864, in Briesen, Prussia. As a child, he displayed a talent for the arts, but became interested in science as a student. During Nernst’s early school and undergraduate years, the German chemical industry became world-dominant in dyestuffs and pharmaceuticals. In 1828, German scientist Friedrich Wöhler discovered that urea could be synthesized from inorganic materials. Wöhler’s work inspired German scientists to design chemical processes to manufacture products previously obtainable only from biological sources. There developed a strong relationship between German industry and German universities to foster this revolutionary notion of basic research aimed at the creation of new products.

As a university student, Nernst attended lectures and laboratory sessions at a variety of institutions in Zurich, Berlin, Graz, and Würzburg, and he was attracted to the outstanding scientists of the day. Nernst first began research at Graz in 1886 under Austrian physicist Ludwig Boltzmann, a champion of the atomistic viewpoint. Nernst soon moved to Würzburg, where he researched electrical currents in solutions under German physicist Friedrich Kohlrausch.

Life’s Work

At the invitation of Wilhelm Ostwald, Nernst accepted a position at the new Physico-Chemical Institute in Leipzig. He continued to study the nature of ions in solution, but he began to include the ideas of German physicist Hermann von Helmholtz and German mathematician Rudolf Clausius. Nernst also began investigating the behavior of ions in a chemical reaction in solution. Helmholtz and Clausius had clarified the concept of spontaneity in a physical process as related to the external work capability of the system. Nernst realized that the idea of external work capability of a chemical system is related to the electrode potential of the reaction embodied in the configuration of a voltaic cell. A voltaic cell (a type of simple battery) is superbly adapted to demonstrate this relation of external work and the electrical potential generated between ions in relation to an electrode. The electrode either donates or accepts the electron charge while, perhaps, it is even involved in the reaction. Nernst supplied the equation that related the concentrations of ions to the external work capability of a cell, which is a means of separating a reaction into donating and accepting cell halves. The overall cell potential, as a combination of these half-cell potentials, is a measure of the chemical potential of the reaction and hence the external work capability. This external work capability has since become known as free energy. The free energy change in a chemical reaction is related to the equilibrium constant for the reaction, or the point of equilibrium as it was then known.

This research earned for Nernst a lectureship at the University of Leipzig. He later accepted a lectureship at Göttingen, where he was promised an assistant professorship. Göttingen had a very high reputation among German universities. In 1894, Nernst became chair of physical chemistry at Göttingen. During his time there, he wrote a physical chemistry text entitled Theoretische Chemie vom Standpunkte der Avogadroschen Regel und der Thermodynamik (Theoretical chemistry from the standpoint of Avogadro’s rule and thermodynamics, 1893). The text was widely used during Nernst’s lifetime, and went through ten subsequent printings. He remained at Göttingen for fifteen years, during which time he also met and married Emma Lohmeyer, the daughter of a local physician. The couple had five children, and lived in a mansion that was provided by the ministry of education and included a new electrochemical laboratory where Nernst served as director. The Nernsts hosted numerous social functions, many of which were for the research assistants at the laboratory. There were as many as forty young people there working toward doctorates, and an extension was eventually added to keep up with the work in progress.

Alfred Bertholet’s explanation of chemical spontaneity in 1867, although of profound impact, was not complete. Bertholet said that spontaneous chemical reactions are those that are exothermic. This theory required much additional work to define the concepts that made it possible to formulate a complete statement of chemical spontaneity. Statements by Sadi Carnot (1824) and Clausius (1850) were crucial to the equations of Helmholtz and Oliver Gibbs. Carnot’s cycle defines a heat engine, operating between two specified temperatures, that converts a given amount of heat into the maximum amount of useful work possible. This heat engine applies to physical as well as chemical processes. Clausius introduced the entropy term S, which is a disorder function that defines the unavailable energy in the process of heat energy conversion to useful work. The equations of Helmholtz and Gibbs were to follow. They state that this maximum amount of useful work is the difference between the total heat energy and that amount that is unavailable for useful work. Nernst’s heat theorem states that, in the equations of Helmholtz and Gibbs, the total heat energy in a chemical reaction and the maximum work available are identical at the absolute zero of temperature. Nernst stated that the specific heat of substances in the condensed phases would become zero at the absolute zero of temperature and therefore S would become zero. With a better understanding of absolute zero, the heat theorem became the third law of thermodynamics: The entropy, S, of a substance (in a perfect crystalline state) may become zero at the absolute zero of temperature, if the absolute of temperature can be reached. S means disorder and thus it is what goes to zero at the absolute zero of temperature instead of energy. It follows, then, that S has a finite positive value at temperatures above absolute zero. Chemists were then able to determine the free energy changes for chemical reactions at a variety of temperatures. This permits the calculation of the equilibrium distribution of mass between reactants and products.

After having received the Nobel Prize for his heat theorem, Nernst spent two years as president of the National Physical Laboratory. He did not like this assignment and returned to academic life as head of the Physics Department at the University of Berlin. During his last years, he purchased a one-thousand-acre estate at Zibelle. The Nernsts permanently retired to Zibelle in 1933, though Nernst maintained an apartment in Berlin for use during his frequent attendance at university functions. Nernst died on November 18, 1941.

Impact

Nernst work had a profound impact on the field of physical chemistry. In addition to expanding existing knowledge of the equilibrium distribution constants for chemical reactions, he wrote the equation for predicting the potential of a voltaic cell in terms of ion concentrations. This equation is essential to the prediction of spontaneity of chemical reactions that can be expressed as electron exchange.

Nernst also sponsored a discussion group every Friday afternoon in his laboratory in the University of Berlin. The group included world-class chemists and physicists such as Albert Einstein, as well as research students. Recent publications and new research findings were brought in for the group to discuss. Nernst’s sponsorship of these weekly colloquia contributed to the revolution in physics and chemistry in the early twentieth century.

Bibliography

Barkan, Diana Kormos. Walter Nernst and the Transition to Modern Physical Science. Cambridge: Cambridge UP, 2011. Print. Presents Nernst’s work in historical context. Provides information about Nernst’s career development and discusses how his work impacted Einstein and Planck.

Bartel, Hans-Georg. Walther Nernst: Pioneer of Physics and of Chemistry. Hackensack: World Scientific, 2007. Print. Biography of Nernst, including details about his professional relationships and his research procedures.

Nernst, Walther. Experimental and Theoretical Applications of Thermodynamics to Chemistry. Toronto: University of Toronto Libraries, 2011. Print. Reprint of Nernst’s work on the third law of thermodynamics, originally published in 1907.