Lars Onsager

Lars Onsager (1903-1976), Norwegian-American chemist and Nobel laureate. Onsager's special interest was the thermodynamics of solutions. For his law of reciprocal relations, later called the zeroth law of thermodynamics, Onsager was awarded the 1968 Nobel Prize in chemistry.

Born in Oslo, Norway, Onsager received his B.S. degree in chemical engineering from the Norwegian Institute of Technology in Trondheim in 1925. In 1928, after emigrating to the United States, he became an associate professor of chemistry at Johns Hopkins University in Baltimore, Maryland. He later joined the faculty of Brown University in Providence, Rhode Island, teaching chemistry and probability statistics. Due to the economics of the Great Depression of the 1930s, Onsager's position at Brown was terminated. He eventually joined the faculty at Yale University in New Haven, Connecticut, in 1932, where he also completed the requirements for a Ph.D. degree in chemistry in 1935. He retired from Yale University in 1972 and taught briefly at the University of Miami in Coral Gables, Florida. There, at age 70, he began to study biophysics and radiationchemistry.

While still an undergraduate in Norway, Onsager greatly amplified and extended a theory of electrolytes (substances that become ions in solution and are capable of conducting electricity) that was known as the Debye-Huckel theory. This theory, formulated by Dutch physicist and Nobel laureate Peter Debye, and his assistant Erich Hueckel, was the first to apply thermodynamics to the understanding of ionization of an electrolyte solution. Onsager furthered this theory by extending the principle of the movements of some ions in a solution to that of all the ions—a pioneering endeavor that led to Onsager's own theoretical studies on thermodynamics. Onsager's research into the motion of ions in solution exposed to an electrical field helped him derive a mathematical theory about how substances behave in solution, the law of reciprocal relations. This law—which became known as the zeroth law of thermodynamics, or the fourth law of thermodynamics—states that if two systems are in thermal equilibrium (see Temperature) with a third system, they are in thermal equilibrium with each other. Onsager's use of mathematical techniques to derive the thermodynamic properties of phase transitions in solids (the change of matter from liquid to a gas to a solid) produced a breakthrough in the 1940s. His continued research into the physics of temperature produced a theoretical explanation for the superfluidity (the frictionless flow of electrons, as in superconductors) of liquid helium. Onsager also developed theories for the statistical properties of liquid crystals and the electrical properties of ice (see Electricity).