Walther Nernst

Walther Hermann Nernst was born in Briesen, West Prussia (now Wąbrzeźno, Poland), on 25 June 1864, the son of a district judge. He studied at Zurich, Berlin, Graz, and Würzburg, and became an assistant to Wilhelm Ostwald at Leipzig in 1887 — arriving at the exact moment when Ostwald, van 't Hoff, and Arrhenius were inventing physical chemistry as a discipline. Nernst became its third generation immediately: at twenty-five he derived the Nernst equation, relating an electrochemical cell's voltage to the concentrations of its reactants, which is still taught in every chemistry course and still printed on every ion-selective electrode's data sheet.

He was, unusually for a theorist of his stature, a relentless inventor. His Nernst lamp — a ceramic filament that glowed without needing a vacuum — was sold to Westinghouse in 1898 for about a million marks, made him wealthy, and was promptly obliterated by the tungsten bulb. He built an early electric piano, drove some of the first motorcars in Göttingen, and applied thermodynamics to his own carp pond. He held chairs at Göttingen and then Berlin, where he was a fixture of the extraordinary physics community that included Planck, Einstein, and von Laue.

His central discovery came from a practical frustration. ΔG = ΔH − TΔS decides whether a reaction proceeds; ΔH was measurable, but ΔS carried an unknown constant of integration that no calorimetry could determine. On 23 December 1906 he presented to the Göttingen Academy his Wärmetheorem: as T → 0, the entropy change of any isothermal process goes to zero, so all substances converge on a common entropy at the bottom and the constant cancels. Chemical equilibrium became calculable from thermal data alone. Planck sharpened it in 1911 by setting the constant to zero, and it became the third law of thermodynamics. Nernst took the 1920 Nobel Prize in Chemistry.

The rest is more complicated. He was among the first to grasp the importance of Einstein's and Planck's quantum work — he organised the 1911 Solvay Congress largely to force the physics establishment to confront it, and personally recruited Einstein to Berlin — yet he remained temperamentally unhappy with quantum theory, having measured one of its most direct consequences before it existed. He signed the 1914 Manifesto of the Ninety-Three defending German war conduct, worked on chemical weapons, and lost both sons at the front. When the Nazis came to power he was forced out for his opposition and for his Jewish sons-in-law, retreated to his country estate at Zibelle, and died there on 18 November 1941. He is buried near Planck and Hilbert in Göttingen.