Nernst , Walther Hermann

(1864–1941) German physical chemist

Nernst, who was born at Briesen in Germany, studied at the universities of Zurich, Berlin, Würzburg, and Graz. After working as assistant to Wilhelm Ostwald in Leipzig from 1887 he became professor of chemistry at Göttingen in 1890. In 1904 he became professor of physical chemistry at Berlin and later was appointed director of the Institute for Experimental Physics there (1924–33). In 1933, out of favor with the Nazis, he retired to his country estate.

Nernst's early work was in electrochemistry – a field in which he made a number of contributions. Thus in 1889 he introduced the idea of the solubility product, i.e., the product of the concentrations of the different types of ions in a saturated solution. The product is a constant for sparingly soluble compounds (at constant temperature). Nernst also suggested (1903) the use of buffer solutions – mixed solutions of weak acids (or bases) and their salts, which resist changes in pH.

His main work, in 1906, was in thermodynamics. It came out of attempts to predict the course of chemical reactions from measurements of specific heats and heats of reaction. If heat is absorbed during a reaction, the amount absorbed falls with temperature and would become zero at absolute zero. Nernst postulated that the rate at which this reduction occurred would also become zero at absolute zero of temperature, and, as a consequence, derived the Nernst heat theorem, which states that if a reaction occurs between pure crystalline solids at absolute zero, then there is no change in entropy.

The theorem, stated in a slightly different form, is now known as the third law of thermodynamics. It is equivalent to the statement that absolute zero cannot be attained in a finite number of steps. At the time it allowed the calculation of absolute values of entropy (and then equilibrium constants), rather than changes in entropy. It is now known to be a consequence of the quantum statistics of the particles. For his work in thermodynamics, Nernst received the Nobel Prize for chemistry in 1920.

He also made contributions to photochemistry and, in addition, produced one of the standard texts of the period, Theoretische Chemie (1893; Theoretical Chemistry), which went through numerous editions and translations.

He managed to make a large fortune by the turn of the century by selling a form of electric light, which though superior to the Edison carbon-filament lamp soon became obsolete with the invention of the tungsten-filament lamp.