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ABSTRACT
Oxidoreduction reactions occur in a wide range of situations, from biological processes such as photosynthesis up to the industrial applications of electrolytic production and including storage and restitution of electric energy in secondary batteries. However the oxidation level of a chemical element, or even the variation in this oxidation level, is insufficient to characterize the ability of compounds to behave as oxidizing or reducing compounds. However, the determination of standard potentials allows for predicting the possibilities of oxidoreduction reactions through thermodynamics. After mentioning briefly the basic principles of oxidoreduction, the article details the methods of access to standard potentials.
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André DARCHEN: Doctor of Physical Sciences - Professor Emeritus, École nationale supérieure de Chimie de Rennes
INTRODUCTION
Redox reactions are a special family of reactions characterized by the involvement of two oxidants (Ox 1 and Ox 2 ) and two reductants (Red 1 and Red 2 ), with the possible participation of redox spectator compounds (CS, CS′), according to the simplified stoichiometry of equation (1) . In fact, in this equation, spectator compounds serve to balance the reaction, but they undergo neither oxidation nor reduction. The oxidizing and reducing compounds belong to two redox couples Ox 1 /Red 1 and Ox 2 /Red 2 :
The definition of an "oxidizing" or "reducing" compound has evolved with scientific knowledge, taking into account possible mechanisms: loss or gain of oxygen, loss or gain of hydrogen, loss or gain of electrons, or variation in oxidation state or oxidation number. To qualify a compound as an oxidizing or reducing agent by means of a redox potential, we will use the definition that refers to the possibility of transferring one or more electrons according to the equation (2) . In this equation, an oxidizer is a compound that can capture electrons, while a reducer is a compound that can supply electrons. According to this equation, the "oxidizing" or "reducing" status of compounds in the oxidation-reduction pair can also be established on the more general basis of the variation in the degree of oxidation of a chemical element present in these compounds.
The oxidant captures...
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Standard redox potentials
Oxidation-reduction, definitions and conventions
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