Redox Reaction

A redox reaction, short for oxidation-reduction reaction, is a chemical reaction in which oxidation and reduction occur together. Oxidation involves the loss of electrons or an increase in oxidation state, while reduction involves the gain of electrons or a decrease in oxidation state. Because the two changes are complementary, oxidation of one chemical species is accompanied by reduction of another .^1,2

A redox reaction can be described in terms of two linked half-reactions. The species that loses electrons is oxidized and acts as a reducing agent because it donates electrons to another species. The species that accepts electrons is reduced and acts as an oxidizing agent because it accepts electrons from and thereby oxidizes the other species. Redox reactions do not necessarily involve oxygen, despite the historical association of oxidation with oxygen .^1,2

Redox reactions are fundamental to biological energy metabolism. During cellular respiration, molecules derived from nutrients are progressively oxidized while electron carriers such as NAD+ are reduced to NADH. NADH can subsequently donate electrons to the mitochondrial electron-transport chain, where a sequence of redox reactions ultimately transfers electrons to oxygen. Part of the free energy released through this controlled electron transfer is used to generate the proton gradient that supports ATP production .³

A redox reaction is therefore broader than either oxidation or reduction alone. Those terms describe the two complementary changes occurring within the overall reaction, whereas “redox reaction” describes the coupled process in which both occur .^1,2