Editing Svante Arrhenius (section)

===Middle period===
[[File:Arrhenius, Svante August – Lehrbuch der kosmischen Physik, 1903 – BEIC 6781113.jpg|thumb|''Lehrbuch der kosmischen Physik'', 1903]]

In 1885, Arrhenius next received a travel grant from the Swedish Academy of Sciences, which enabled him to study with Ostwald in [[Riga]] (now in [[Latvia]]), with [[Friedrich Kohlrausch (physicist)|Friedrich Kohlrausch]] in [[Würzburg]], [[Germany]], with [[Ludwig Boltzmann]] in [[Graz, Austria]], and with [[Jacobus Henricus van 't Hoff]] in [[Amsterdam]].

In 1889, Arrhenius explained the fact that most reactions require added heat energy to proceed by formulating the concept of [[activation energy]], an energy barrier that must be overcome before two molecules will react. The [[Arrhenius equation]] gives the quantitative basis of the relationship between the activation energy and the rate at which a reaction proceeds.

In 1891, he became a lecturer at the Stockholm University College (''Stockholms Högskola'', now [[Stockholm University]]), being promoted to professor of physics (with much opposition) in 1895, and [[Rector (academia)|rector]] in 1896.