Reaktion

Reaktion (die Reaktion) is the German noun for "reaction." It denotes a response, change, or process triggered by a cause. The term is common in science, philosophy, and everyday language, and it appears in many compound words such as Kettenreaktion or Gegenreaktion. The related adjective is reaktionär, meaning reactionary.

In science, a chemical reaction is a process in which reactants are transformed into products, often accompanied by energy changes. Reactions are described by stoichiometry, thermodynamics, and kinetics. The rate of a reaction depends on factors such as concentration, temperature, surface area, and the presence of catalysts. Some reactions are reversible and can reach equilibrium when forward and reverse rates are equal.

Beyond chemistry, Reaktion is used to describe responses in biology, medicine, physics, and social contexts. In biology and medicine, reactions can refer to physiological responses to stimuli or immune responses. In physics, nuclear and chemical chain reactions are notable examples. In everyday language, to react means to respond to an event or stimulus, and the noun can refer to the observable outcome of that response.

Etymology and cognates: Reaktion comes from Latin reactio, through French réaction, and into German with the same meaning as in English “reaction.” In German usage, many common compounds label specific types of reactions, such as Reaktionszeit (reaction time) or Reaktionsmechanismus (reaction mechanism). The term thus spans scientific disciplines and everyday speech.