Electrochemistry Fundamental Concepts Oxidation occurs when a chemical species looses an electron.
Reduction is when a species gains an electron.
The iron is oxidized while the cerium is reduced. An oxidant species promotes oxidation and a reductant promotes reduction. The above reaction, cerium is the oxidant or oxidation agent while iron is the reductant or reducing agent . For example, the generic reaction has a Q where the A are activities. Calculations of equilibrium constants from tables of reduction potentials.