A chemical reactor is a device in which change in composition of matter occurs by chemical reaction. The chemical reaction is normally the most important change, and the reactor is designed to accomplish that change. A reactor is usually the “heart” of an overall chemical process. Most industrial chemical processes are operated for the purpose of producing chemical products such as ammonia and petrochemicals. Reactors are also involved in energy production, as in engines and in certain electrochemical cells.

Chemical kinetics is concerned with the rates of chemical reactions, that is, with the quantitative description of how fast chemical reactions occur, and the factors affecting these rates. On the other hand, chemical reaction engineering is concerned with the rational design and/or analysis of performance of chemical reactors.