Arrhenius, Svante August (1859-1927), Swedish chemist, who helped lay the foundations of modern chemistry. Born near Uppsala, Sweden, he was educated at the University of Uppsala and received his Ph.D. in 1884. While still a student, he studied the conductive properties of electrolytic (charge-conducting) solutions. In his doctoral thesis he formulated the theory of electrolytic dissociation. This theory holds that in electrolytic solutions, the dissolved chemical compounds in the solution are dissociated into ions, even when there is no current flowing through the solution. Arrhenius also postulated that the degree of dissociation increases as the solution becomes more dilute—this hypothesis later turned out to be true only for weak electrolytes. His theory was initially thought to be wrong, and his thesis was given the lowest possible passing grade. Later, however, Arrhenius' theory of electrolytic dissociation became generally accepted, and eventually became one of the cornerstones of modern physical chemistry and electrochemistry.
In 1889 Arrhenius also observed that the speed of chemical reactions increases markedly when the temperature is increased, at a rate proportional to the concentration of the activated molecules. Arrhenius became professor of chemistry at the University of Stockholm in 1895 and director of the Nobel Institute of Physical Chemistry in 1905. His awards and honours include the 1903 Nobel Prize in chemistry. He wrote works on physical and biological chemistry, electrochemistry, and astronomy. In astronomy he is noted for his suggestion that life on earth originated from living spores driven through space by the pressure of light.