Here are some phrases used in chemical reaction engineering:

Chemical Reaction Engineering

Chemical reaction engineering is the proper bringing to practice of chemical reactions. This definition stems from one of the founding fathers of chemical engineering; Octave Levenspiel. An additional definition is given by the key equation: reactor performance is a function of inputs, kinetics, and contacting.

Continuously Stirred Tank Reactor (CSTR)

CSTR is a theoretical concept of a fully back-mixed reactor in continuous operation mode. Octave Levenspiel calls it a Mixed Flow Reactor (MFR).

Westerterp calls this concept the Continuously Ideally Stirred Tank Reactor (CISTR). This stresses the assumption that it is ideally mixed.

The CSTR term is often misused for a batch operated mechanically stirred tank reactor. Such a reactor however has plug flow behavior, so it is the opposite of a fully back-mixed reactor.

Plug Flow Reactor (PFR)

This is a theoretical concept of a reactor in which each fluid element has the same residence time. So, the fluid flows as a plug through the reactor, or the fluid elements stay the same time in the reactor. This latter can occur for instance in a batch reactor, with all feeds entered at the start of the batch operation.

The misconception sometimes is that it is about a real pipe reactor. A real pipe reactor, however, may show a considerably wide residence time distribution of the individual fluid elements.

Reaction rate ( r )      

Reaction rate is the rate at which a molecular species is formed or disappears by a chemical reaction per unit fluid volume. It is an intensive variable, like temperature, or pressure are intensive variables.

The reaction rate depends in the local conditions in the reaction system. It is independent on the type of reactor system itself.

Source of information

These definitions and  far more information on chemical reaction engineering is available in the new book:

Multiphase reactors – Reaction Engineering Concepts, Selection, and Industrial Applications, by Jan Harmsen, René Bos, DE GRUYTER, Berlin (2023).