Chemical Reactions

Reduction-Oxidation

Redox Reactions (Reduction-Oxidation Reactions) is a name given to chemical reactions where electrons are gained and lost by atoms, ions, or molecules.   Oxidation means the loss of electrons, gain of oxygen, or loss of hydrogen by an atom, ion, or molecule during a chemical reaction.   Reduction means the gain of electrons, loss of oxygen, or gain of hydrogen by an atom, ion, or molecule during a chemical reaction.   Note that in a redox reaction, reduction must accompany oxidation and vice-versa, since electrons lost by one particle must be gained by another particle to conserve total mass.   An example of a redox reaction is the combination of hydrogen with fluorine to produce hydrogen fluoride (e = electron):

H₂ ——> 2H⁺ + 2e^¯

F₂ + 2e^¯ ——> 2F^¯

The electrons on both sides cancel each other other's charge, so they can be added to obtain

2H⁺ + 2F^¯ ——> 2HF (equation in ionic form)

or     H₂ + F₂ ——> 2HF (equation in molecular form)

The substance that loses electrons is called the reducing agent (reductant) and the substance that gains electrons is called the oxidizing agent (oxidant).   The oxidizing agent is always reduced in a redox reaction, while the reducing agent is always oxidized.

Many biological processes are redox reactions.   Photosynthesis includes the reduction of carbon dioxide into sugars and the oxidation of water into molecular oxygen.   The reverse reaction, respiration, oxidizes sugars to produce carbon dioxide and water.   Batteries function through redox reactions as do electrolysis reactions to separate metals and other compounds.

Hydrolysis, Condensation and Hydration Reactions ^{Wiki n.p.}