Redox (Oxidation/Reduction) Potential is a measure of a tendency, either gain or lose electrons when it is subject with a new species. A chemical reaction in which electrons are transferred from one atom (which is oxidized) to another atom (which is reduced).
The Redox Potential is a measure (in Volts) of the affinity of a substance for electrons, it is electro-negativity, compared with hydrogen (which is set at 0). Substances are more strongly electronegative than (i.e. capable of oxidizing) hydrogen have positive redox potentials. Substances are less electronegative than (i.e. capable of reducing) hydrogen have negative redox potentials.
Oxidations and Reduction always go together. They are called Redox Reactions. Oxidation means losing of electrons. Reduction means receiving (or gaining) of electrons.
This figure is a favorite mnemonic to understand the Redox potential and also very descriptive and informative of this process, I hope so[1].
Fig: Oxidation & Reduction
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