Portrait of the German physical chemist Hermann Walther Nernst, 1864-1941. Nernst worked on the application of physics to chemical problems. He gained a professorship in Berlin in 1905. He proposed the third law of thermodynamics: entropy change approaches zero at a temperature of absolute zero. From this is deduced the impossibility of obtaining absolute zero. This work earned Nernst the 1920 Nobel Prize for chemistry. He also explained how hydrogen and chlorine explode on exposure to light, the result of a chain reaction. He worked on the ionisation of compounds in water, and invented an electric lamp.