Combustion is an example of an oxidation-reduction reaction.
When a chemical bond forms, the bonding electrons enter a molecular orbital within the internuclear space pulling the bonded atoms together. This represents an electrostatic potential energy decrease. When there is an electronegativity difference between two atoms, the more electronegative atom pulls the electron or electrons the other atom has brought to the new bond inward towards its more powerful nucleus. This drawing in of negative charge by the more electronegative atom increases the magnitude of internal energy decrease above and beyond what is normally seen. This extra energy makes polar bonds stronger. As a general rule, they release more energy when they form. This phenomenon is the basis of oxidation-reduction. Oxidation-reduction is simply an accounting system to keep track of the extra energy released when a very electronegative element (high reduction potential) gains electron control (is reduced). Oxidation-reduction tells the story in terms of a simple narrative of electron control.
As a framework which lends a great deal of coherence to biochemistry, oxidation-reduction is one of the most important topics in physical science for future doctors. The central narrative of bioenergetics, for example, is the transduction of redox potential into phosphoryl transfer potential.
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Conceptual Vocabulary for Oxidation-Reduction
Redox, shorthand for reduction/oxidation reaction, is a term used to describe chemical reactions in which atoms have their oxidation state changed.
An oxidizing agent is a substance that gains electrons in a redox chemical reaction.
A reducing agent is the element or a compound that reduces another species in a redox reaction. It is the electron donor in the redox.
Within a molecule or complex, the oxidation number of an element is the charge that it would have if the compound were composed of ions, with assignment of shared electrons based on electronegativity.
The oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. It is usually numerically equal to the oxidation number.
A half reaction is either the oxidation or reduction reaction component of a redox reaction.
Standard reduction potential is the tendency of a chemical species to acquire electrons and thereby be reduced.
Electron transfer is the process by which an electron moves from one atom or molecule to another atom or molecule.
A terminal electron acceptor is a compound that receives or accepts an electron during cellular respiration or photosynthesis.
In general terms, an electron donor gives up an electron during cellular respiration.
Superoxide is the free radical product of the one-electron reduction of dioxygen.
A peroxide is a compound containing an oxygen-oxygen single bond.
Metathesis is a bimolecular process involving the exchange of bonds between the two reacting chemical species, which results in the creation of products with similar or identical bonding affiliations.
Denitrification is the process of reducing nitrate and nitrite, which can be thought of as the opposite of nitrogen fixation
An oxidoreductase is an enzyme that catalyzes the transfer of electrons from one molecule to another.
Inner sphere electron transfer proceeds via a covalent linkage between the two redox partners, the oxidant and the reductant.
Outer sphere electron transfer refers to an electron transfer event that occurs between chemicals that remain separate species before, during, and after the electron transfer event.
Osmium tetroxide is the chemical compound with one oxmium atom bonded to four oxygens. It is an important oxidizing agent in the laboratory.
Perchlorates are the salts derived from perchloric acid, which are important oxidizing agents for their tendency not to react unless heated.
Redox signaling is the concept that free radicals, reactive oxygen species, and other electronically-activated species act as messengers in biological systems.
Marcus Theory was originally developed to explain outer sphere electron transfer, but was later extended to inner sphere electron transfer by Noel Hush.