ABSTRACT
Redox reactions are numerous in biochemistry. Among them, perhaps the most known are those involving cytochromes. The definition of couples redox and the measurement of their standard potentials permit to class them according to their oxidative and reductive power. A redox reaction results from the exchange of electrons between two redox couples or pairs. Redox reactions can take place in a homogenous phase or in a heterogeneous medium, on the surface of electrodes, that is to say in an electrochemical cell. An electrochemical cell is said to be reversible if the direction of the reaction cell is inverted when the electron flow is inverted. It is irreversible when a new reaction cell appears. The values of electrode potentials permit to easily predict redox reactions. From the qualitative standpoint, the simplest way to predict the direction of a redox reaction is to compare the standard potentials of the two couples which may react together in the investigated reaction.
