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Redox (reduction–oxidation, pronunciation: or ) is a type of
chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and t ...

chemical reaction
in which the
oxidation state The oxidation state, or oxidation number, is the hypothetical charge Charge or charged may refer to: Arts, entertainment, and media Films * ''Charge, Zero Emissions/Maximum Speed'', a 2011 documentary Music * Charge (David Ford album), ''Charge ...
s of
atoms An atom is the smallest unit of ordinary that forms a . Every , , , and is composed of neutral or atoms. Atoms are extremely small, typically around 100 s across. They are so small that accurately predicting their behavior using —as ...

atoms
are changed. Redox reactions are characterized by the actual or formal transfer of
electron The electron is a subatomic particle (denoted by the symbol or ) whose electric charge is negative one elementary charge. Electrons belong to the first generation (particle physics), generation of the lepton particle family, and are general ...

electron
s between
chemical species A chemical species is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touc ...
, most often with one species (the
reducing agent A reducing agent (also called a reductant, reducer, or electron donor) is an element or compound that loses or "donates" an electron The electron is a subatomic particle In physical sciences, subatomic particles are smaller than atom ...
) undergoing oxidation (losing electrons) while another species (the
oxidizing agent 125px, Dangerous goods label for oxidizing agents An oxidizing agent, also known as an oxidant or oxidizer, is a substance that has the ability to oxidize (mild reducing agent) are added to powdered potassium permanganate (strong oxidizi ...

oxidizing agent
) undergoes reduction (gains electrons). The chemical species from which the electron is removed is said to have been oxidized, while the chemical species to which the electron is added is said to have been reduced. In other words: * Oxidation is the ''loss'' of electrons or an ''increase'' in the oxidation state of an atom, an
ion An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ...
, or of certain atoms in a
molecule A molecule is an electrically Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In physics, motion is the phenomenon ...

molecule
. * Reduction is the ''gain'' of electrons or a ''decrease'' in the oxidation state of an atom, an ion, or of certain atoms in a molecule (a reduction in oxidation state). Many reactions in organic chemistry are redox reactions due to changes in oxidation states but without distinct electron transfer. For example, during the
combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion ...
of wood with molecular oxygen, the oxidation state of carbon atoms in the wood increases and that of
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
atoms decreases as carbon dioxide and water are formed. The oxygen atoms undergo reduction, formally gaining electrons, while the carbon atoms undergo oxidation, losing electrons. Thus oxygen is the oxidizing agent and carbon is the reducing agent in this reaction. Although oxidation reactions are commonly associated with the formation of oxides from oxygen molecules, oxygen is not necessarily included in such reactions, as other chemical species can serve the same function. Redox reactions can occur relatively slowly, as in the formation of
rust Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous ferric oxides, hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxi ...

rust
, or much more rapidly, as in the case of burning fuel. There are simple redox processes, such as the oxidation of
carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's crust. Three occur naturally, ...

carbon
to yield
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
(CO2) or the reduction of carbon by
hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the che ...

hydrogen
to yield
methane Methane (, ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Earth ...
(CH4), and more complex processes such as the oxidation of
glucose Glucose is a simple with the . Glucose is the most abundant , a subcategory of s. Glucose is mainly made by and most during from water and carbon dioxide, using energy from sunlight, where it is used to make in s, the most abundant carbohydr ...

glucose
(C6H12O6) in the human body. Analysis of bond energies and ionization energies in water allow calculation of the redox potentials.


Etymology

"Redox" is a
portmanteau A portmanteau (, ) or portmanteau word (from "portmanteau (luggage) A portmanteau is a piece of luggage Baggage or luggage consists of bags, cases, and containers which hold a travel Travel is the movement of people between distant ...

portmanteau
of the words "reduction" and "oxidation". The word ''oxidation'' originally implied reaction with oxygen to form an oxide, since
dioxygenThere are several known allotropy, allotropes of oxygen. The most familiar is oxygen, molecular oxygen (O2), present at significant levels in Atmosphere of Earth, Earth's atmosphere and also known as dioxygen or triplet oxygen. Another is the highl ...
(O2(''g'')) was historically the first recognized
oxidizing agent 125px, Dangerous goods label for oxidizing agents An oxidizing agent, also known as an oxidant or oxidizer, is a substance that has the ability to oxidize (mild reducing agent) are added to powdered potassium permanganate (strong oxidizi ...

oxidizing agent
. Later, the term was expanded to encompass oxygen-like substances that accomplished parallel chemical reactions. Ultimately, the meaning was generalized to include all processes involving the loss of electrons. The word ''reduction'' originally referred to the loss in weight upon heating a metallic
ore ore – psilomelane Psilomelane is a group name for hard black manganese oxides including hollandite and romanechite. Psilomelane consists of hydrous manganese Manganese is a chemical element Image:Simple Periodic Table Chart- ...

ore
such as a
metal oxide of rutile Rutile is a mineral composed primarily of titanium dioxide (TiO2), and is the most common natural form of TiO2. Other rarer polymorphs of TiO2 are known, including anatase, akaogiite, and brookite. Rutile has one of the highest re ...
to extract the metal. In other words, ore was "reduced" to metal.
Antoine Lavoisier Antoine-Laurent de Lavoisier ( , ,; 26 August 17438 May 1794), When reduced without charcoal, it gave off an air which supported respiration and combustion in an enhanced way. He concluded that this was just a pure form of common air and th ...

Antoine Lavoisier
demonstrated that this loss of weight was due to the loss of oxygen as a gas. Later, scientists realized that the metal atom gains electrons in this process. The meaning of ''reduction'' then became generalized to include all processes involving a gain of electrons. The electrochemist
John Bockris Bernhardt Patrick John O’Mara Bockris (5 January 1923 – 7 July 2013) was a professor of chemistry, latterly at Texas A&M University. During his long and prolific career he published some 700 papers and two dozen books. His best known wor ...
has used the words ''electronation'' and ''deelectronation'' to describe reduction and oxidation processes, respectively, when they occur at
electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor A semiconductor material has an Electrical resistivity and conductivity, electrical conductivity value falling between tha ...

electrode
s. These words are analogous to
protonation In chemistry, protonation (or hydronation) is the addition of a proton (or hydron, or hydrogen cation), (H+) to an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance ...
and
deprotonation Deprotonation (or dehydronation) is the removal (transfer) of a proton A proton is a subatomic particle, symbol or , with a positive electric charge of +1''e'' elementary charge and a mass slightly less than that of a neutron. Protons and neutro ...

deprotonation
, but they have not been widely adopted by chemists worldwide. The term "hydrogenation" could often be used instead of reduction, since hydrogen is the reducing agent in a large number of reactions, especially in organic chemistry and biochemistry. However, unlike oxidation, which has been generalized beyond its root element, hydrogenation has maintained its specific connection to reactions that ''add'' hydrogen to another substance (e.g., the hydrogenation of unsaturated fats into saturated fats, R−CH=CH−R + H2 → R−CH2−CH2−R). The word "redox" was first used in 1928.


Definitions

The processes of oxidation and reduction occur simultaneously and cannot happen independently of one another, similar to
acid–base reaction An acid–base reaction is a chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical react ...
s. The oxidation alone and the reduction alone are each called a ''
half-reaction A half reaction (or half-cell reaction) is either the oxidation or reduction reaction component of a redox (mild reducing agent) are added to powdered potassium permanganate Potassium permanganate is an inorganic compound with the chemical ...
'' because two half-reactions always occur together to form a whole reaction. When writing half-reactions, the gained or lost electrons are typically included explicitly in order that the half-reaction be
balanced In telecommunication Telecommunication is the transmission of information Information can be thought of as the resolution of uncertainty; it answers the question of "What an entity is" and thus defines both its essence and the nature of i ...
with respect to electric charge. The electrons cancel out when the half-reactions are combined to make the net
chemical equation A chemical equation is the symbolic representation of a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter In classical ...
. Though sufficient for many purposes, these general descriptions are not precisely correct. Although oxidation and reduction properly refer to ''a change in
oxidation state The oxidation state, or oxidation number, is the hypothetical charge Charge or charged may refer to: Arts, entertainment, and media Films * ''Charge, Zero Emissions/Maximum Speed'', a 2011 documentary Music * Charge (David Ford album), ''Charge ...
'', the actual transfer of electrons may never occur. The oxidation state of an atom is the fictitious charge that an atom would have if all bonds between atoms of different elements were 100% ionic. Thus, oxidation is best defined as an ''increase in oxidation state'', and reduction as a ''decrease in oxidation state''. In practice, the transfer of electrons will always cause a change in the oxidation state, but there are many reactions that are classed as "redox" even though no electron transfer occurs (such as those involving
covalent A covalent bond is a chemical bond A chemical bond is a lasting attraction between atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and take ...

covalent
bonds). As a result, simple half-reactions cannot be written for the individual atoms undergoing a redox process.


Oxidizing and reducing agents

In redox processes, the reductant transfers electrons to the oxidant. Thus, in the reaction, the reductant or ''reducing agent'' loses electrons and is oxidized, and the oxidant or ''oxidizing agent'' gains electrons and is reduced. The pair of an oxidizing and reducing agent that is involved in a particular reaction is called a ''redox pair''. A ''redox couple'' is a reducing species and its corresponding oxidizing form, e.g., / .


Oxidizers

Substances that have the ability to ''oxidize'' other substances (cause them to lose electrons) are said to be ''oxidative'' or ''oxidizing'', and are known as
oxidizing agent 125px, Dangerous goods label for oxidizing agents An oxidizing agent, also known as an oxidant or oxidizer, is a substance that has the ability to oxidize (mild reducing agent) are added to powdered potassium permanganate (strong oxidizi ...

oxidizing agent
s, oxidants, or oxidizers. That is, the oxidant (oxidizing agent) removes electrons from another substance, and is thus itself reduced. And, because it "accepts" electrons, the oxidizing agent is also called an
electron acceptor An electron acceptor is a chemical entity that accepts electron The electron is a subatomic particle (denoted by the symbol or ) whose electric charge is negative one elementary charge. Electrons belong to the first generation (particle phy ...
.
Oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

Oxygen
is the quintessential oxidizer. Oxidants are usually chemical substances with elements in high oxidation states (e.g., , , , , ), or else highly
electronegative Electronegativity, symbolized as ''Chi (letter), χ'', is the tendency of an atom to attract shared electrons (or electron density) to itself. An atom's electronegativity is affected by both its atomic number and the distance at which its valence ...

electronegative
elements (, , , ) that can gain extra electrons by oxidizing another substance.


Reducers

Substances that have the ability to ''reduce'' other substances (cause them to gain electrons) are said to be ''reductive'' or ''reducing'' and are known as
reducing agent A reducing agent (also called a reductant, reducer, or electron donor) is an element or compound that loses or "donates" an electron The electron is a subatomic particle In physical sciences, subatomic particles are smaller than atom ...
s, reductants, or reducers. The reductant (reducing agent) transfers electrons to another substance and is thus itself oxidized. And, because it donates electrons, the reducing agent is also called an
electron donorAn electron donor is a chemical entity that donates electron The electron is a subatomic particle, symbol or , whose electric charge Electric charge is the physical property of matter that causes it to experience a force when placed in an el ...
. Electron donors can also form
charge transfer complex A charge-transfer (CT) complex or electron-donor-acceptor complex is an association of two or more molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five ...
es with electron acceptors. Reductants in chemistry are very diverse.
Electropositive Electronegativity, symbolized as '' χ'', is the tendency of an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. ...
elemental
metal A metal (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is appro ...

metal
s, such as
lithium Lithium (from el, λίθος, lithos, lit=stone) is a with the Li and  3. It is a soft, silvery-white . Under , it is the least dense metal and the least dense solid element. Like all alkali metals, lithium is highly and flammable, a ...

lithium
,
sodium Sodium is a with the  Na (from Latin ''natrium'') and  11. It is a soft, silvery-white, highly reactive . Sodium is an , being in of the periodic table. Its only stable is 23Na. The free metal does not occur in nature, and must be ...

sodium
,
magnesium Magnesium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science ...

magnesium
,
iron Iron () is a with Fe (from la, ) and 26. It is a that belongs to the and of the . It is, on , right in front of (32.1% and 30.1%, respectively), forming much of Earth's and . It is the fourth most common . In its metallic state, iron ...

iron
,
zinc Zinc is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical element ...

zinc
, and
aluminium Aluminium (aluminum in and ) is a with the  Al and  13. Aluminium has a density lower than those of other common , at approximately one third that of . It has a great affinity towards , and of on the surface when exposed to air ...

aluminium
, are good reducing agents. These metals donate or ''give away'' electrons relatively readily. ''Hydride transfer reagents'', such as and , are widely used in
organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and th ...
, primarily in the reduction of
carbonyl In organic chemistry Organic chemistry is a branch of chemistry that studies the structure, properties and reactions of organic compounds, which contain carbon in covalent bonding.Clayden, J.; Greeves, N. and Warren, S. (2012) ''Organic Chemistr ...

carbonyl
compounds to
alcohols In chemistry, alcohol is an organic compound that carries at least one hydroxyl functional group (−OH) bound to a Saturated and unsaturated compounds, saturated carbon atom. The term alcohol originally referred to the primary alcohol ethan ...

alcohols
. Another method of reduction involves the use of hydrogen gas (H2) with a
palladium Palladium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

palladium
,
platinum Platinum is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

platinum
, or
nickel Nickel is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

nickel
catalyst that utilizes a low-temperature oxidation catalyst to convert carbon monoxide to less toxic carbon dioxide at room temperature. It can also remove formaldehyde from the air. Catalysis () is the process of increasing the reaction rate, rate of a ...

catalyst
. The
catalytic hydrogenation Hydrogenation is a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical A chemical substance is a form of matter having constant ...
reaction is an important industrial process.


Standard electrode potentials (reduction potentials)

Each half-reaction has a ''standard
electrode potential In electrochemistry, electrode potential is the electromotive force In electromagnetism and electronics, electromotive force (emf, denoted \mathcal and measured in volts) is the electrical action produced by a non-electrical source. Devices (kno ...
'' (''E''), which is equal to the potential difference or
voltage Voltage, electric potential difference, electric pressure or electric tension is the difference in electric potential The electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is the ...

voltage
at equilibrium under
standard conditions Standard temperature and pressure (STP) are standard Standard may refer to: Flags * Colours, standards and guidons * Standard (flag), a type of flag used for personal identification Norm, convention or requirement * Standard (metrology), a ...
of an
electrochemical cell An electrochemical cell is a device capable of either generating electrical energy Electrical energy is energy derived from electric potential energy or kinetic energy. When used loosely, ''electrical energy'' refers to energy that has been c ...
in which the
cathode A cathode is the from which a leaves a polarized electrical device. This definition can be recalled by using the ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in which positive charges move. Electrons ha ...
reaction is the
half-reaction A half reaction (or half-cell reaction) is either the oxidation or reduction reaction component of a redox (mild reducing agent) are added to powdered potassium permanganate Potassium permanganate is an inorganic compound with the chemical ...
considered, and the
anode An anode is an electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor A semiconductor material has an Electrical resistivity and conductivity, electrical conductivit ...

anode
is a
standard hydrogen electrode The standard hydrogen electrode (abbreviated SHE), is a redox electrode which forms the basis of the thermodynamic scale of oxidation-reduction potentials. Its absolute electrode potential is estimated to be at 25 °C, but to form a basis ...

standard hydrogen electrode
where hydrogen is oxidized: : H2 → H+ + e. The electrode potential of each half-reaction is also known as its ''reduction potential'' ''E'', or potential when the half-reaction takes place at a cathode. The reduction potential is a measure of the tendency of the oxidizing agent to be reduced. Its value is zero for H+ + e →  H2 by definition, positive for oxidizing agents stronger than H+ (e.g., +2.866 V for F2) and negative for oxidizing agents that are weaker than H+ (e.g., −0.763 V for Zn2+). For a redox reaction that takes place in a cell, the potential difference is: :''E'' = ''E'' – ''E'' However, the potential of the reaction at the anode is sometimes expressed as an ''oxidation potential'': :''E'' = –''E''. The oxidation potential is a measure of the tendency of the reducing agent to be oxidized but does not represent the physical potential at an electrode. With this notation, the cell voltage equation is written with a plus sign :''E'' = ''E'' + ''E''


Examples of redox reactions

In the reaction between
hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the che ...

hydrogen
and
fluorine Fluorine is a chemical element with the Chemical symbol, symbol F and atomic number 9. It is the lightest halogen and exists at Standard conditions for temperature and pressure, standard conditions as a highly toxic, pale yellow Diatomic molecule ...

fluorine
, hydrogen is being oxidized and fluorine is being reduced: : + → 2 HF This reaction is spontaneous and releases 542 kJ per 2 g of hydrogen because the H-F bond is much stronger than the weak, high-energy F-F bond. We can write this overall reaction as two
half-reaction A half reaction (or half-cell reaction) is either the oxidation or reduction reaction component of a redox (mild reducing agent) are added to powdered potassium permanganate Potassium permanganate is an inorganic compound with the chemical ...
s: the oxidation reaction: : → 2  H+ + 2  and the reduction reaction: : + 2 e → 2  F Analyzing each half-reaction in isolation can often make the overall chemical process clearer. Because there is no net change in charge during a redox reaction, the number of electrons in excess in the oxidation reaction must equal the number consumed by the reduction reaction (as shown above). Elements, even in molecular form, always have an oxidation state of zero. In the first half-reaction, hydrogen is oxidized from an oxidation state of zero to an oxidation state of +1. In the second half-reaction, fluorine is reduced from an oxidation state of zero to an oxidation state of −1. When adding the reactions together the electrons are canceled: : And the ions combine to form
hydrogen fluoride Hydrogen fluoride is a chemical compound with the chemical formula . This colorless gas or liquid is the principal industrial source of fluorine, often as an aqueous solution called hydrofluoric acid. It is an important feedstock in the preparation ...
: :2 H+ + 2 F → 2 HF The overall reaction is: : + → 2 HF


Metal displacement

In this type of reaction, a metal atom in a compound (or in a solution) is replaced by an atom of another metal. For example,
copper Copper is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

copper
is deposited when
zinc Zinc is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical element ...

zinc
metal is placed in a
copper(II) sulfate Copper(II) sulfate, also known as copper sulphate, are the inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. However, the ...
solution: Zn(s)+ CuSO4(aq) → ZnSO4(aq) + Cu(s) In the above reaction, zinc metal displaces the copper(II) ion from copper sulfate solution and thus liberates free copper metal. The reaction is spontaneous and releases 213 kJ per 65 g of zinc because relative to zinc, copper metal is lower in energy due to bonding via its partially filled d-orbitals. The ionic equation for this reaction is: :Zn + Cu2+ → Zn2+ + Cu As two
half-reaction A half reaction (or half-cell reaction) is either the oxidation or reduction reaction component of a redox (mild reducing agent) are added to powdered potassium permanganate Potassium permanganate is an inorganic compound with the chemical ...
s, it is seen that the zinc is oxidized: :Zn → Zn2+ + 2 e And the copper is reduced: :Cu2+ + 2 e → Cu


Other examples

* The reduction of
nitrate Nitrate is a polyatomic ion A polyatomic ion, also known as a molecular ion, is a covalently bonded A covalent bond is a chemical bond A chemical bond is a lasting attraction between atoms, ions or molecules that enables the format ...

nitrate
to
nitrogen Nitrogen is the chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science ...

nitrogen
in the presence of an acid (
denitrification Denitrification is a microbially facilitated process where nitrate (NO3−) is reduced and ultimately produces molecular nitrogen Nitrogen is the chemical element with the Symbol (chemistry), symbol N and atomic number 7. It was first discove ...
):2NO3- + 10e- + 12H+ -> N2 + 6 H2O * The
combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion ...
of
hydrocarbon In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, prop ...
s, such as in an
internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine In thermodynamics and engineering, a heat engine is a system that converts heat to mechanical energy, which can then be used to do work (physics), mechanical work. It doe ...

internal combustion engine
, produces
water Water (chemical formula H2O) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known li ...

water
,
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
, some partially oxidized forms such as
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom. It is the simplest molecule of the oxocarbon family. In ...

carbon monoxide
, and heat
energy In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regula ...

energy
. Complete oxidation of materials containing
carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's crust. Three occur naturally, ...

carbon
produces carbon dioxide. * The stepwise oxidation of a hydrocarbon by oxygen, in
organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and th ...
, produces water and, successively: an
alcohol In chemistry, alcohol is an organic compound that carries at least one hydroxyl functional group (−OH) bound to a Saturated and unsaturated compounds, saturated carbon atom. The term alcohol originally referred to the primary alcohol ethan ...

alcohol
, an
aldehyde Chemically, an aldehyde is a compound containing a functional group In organic chemistry, a functional group is a substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same fu ...

aldehyde
or a
ketone In chemistry, a ketone is a functional group with the structure R2C=O, where R can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (a carbon-oxygen double bond). The simplest ketone is acetone (R = R' = methyl) ...
, a
carboxylic acid A carboxylic acid is an organic acid that contains a carboxyl group (C(=O)OH) attached to an R-group. The general formula of a carboxylic acid is R−COOH or R−CO2H, with substituent, R referring to the alkyl, alkenyl, aryl, or other group. ...
, and then a
peroxide Peroxides are a group of compounds with the structure R−O−O−R, where R = any element. The O−O group in a peroxide is called the peroxide group or peroxo group. The nomenclature is somewhat variable. The most common peroxide is hydrogen p ...

peroxide
.


Corrosion and rusting

* The term
corrosion Corrosion is a that converts a refined metal into a more chemically stable form such as , , or . It is the gradual destruction of materials (usually a ) by chemical and/or electrochemical reaction with their environment. is the field dedica ...

corrosion
refers to the electrochemical oxidation of metals in reaction with an oxidant such as oxygen.
Rust Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous ferric oxides, hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxi ...

Rust
ing, the formation of
iron oxide Iron oxides are chemical compounds composed of iron and oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, ...

iron oxide
s, is a well-known example of electrochemical corrosion; it forms as a result of the oxidation of
iron Iron () is a with Fe (from la, ) and 26. It is a that belongs to the and of the . It is, on , right in front of (32.1% and 30.1%, respectively), forming much of Earth's and . It is the fourth most common . In its metallic state, iron ...

iron
metal. Common rust often refers to
iron(III) oxide Iron(III) oxide or ferric oxide is the inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. However, the distinction is ...
, formed in the following chemical reaction:4Fe + 3O2 -> 2Fe2O3 * The oxidation of iron(II) to iron(III) by
hydrogen peroxide Hydrogen peroxide is a chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by hav ...

hydrogen peroxide
in the presence of an acid:Fe^ -> + e-H2O2 + 2e- -> 2OH- Overall equation: + + 2H+ -> + 2H2O


Disproportionation

A
disproportionation In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds composed of atoms, mo ...

disproportionation
reaction is one in which a single substance is both oxidized and reduced. For example,
thiosulfate Thiosulfate () (IUPAC-recommended spelling; sometimes thiosulphate in British English) is an Sulfur oxoacid, oxyanion of sulfur. The prefix thio- indicates that the thiosulfate ion is a sulfate ion with one oxygen replaced by sulfur. Thiosulfate h ...
ion with sulfur in oxidation state +2 can react in the presence of acid to form elemental sulfur (oxidation state 0) and
sulfur dioxide Sulfur dioxide (IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering OrganizationsNational Adhering Organizations in chemistry are the organizations that work as the autho ...
(oxidation state +4). :S2O32-(aq) + 2 H+(aq) → S(s) + SO2(g) + H2O(l) Thus one sulfur atom is reduced from +2 to 0, while the other is oxidized from +2 to +4.


Redox reactions in industry

Cathodic protection Cathodic protection (CP; ) is a technique used to control the corrosion of a metal surface by making it the cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be reca ...
is a technique used to control the corrosion of a metal surface by making it the cathode of an electrochemical cell. A simple method of protection connects protected metal to a more easily corroded "
sacrificial anode A galvanic anode, or sacrificial anode, is the main component of a galvanic cathodic protection Cathodic protection (CP; ) is a technique used to control the corrosion of a metal surface by making it the cathode A cathode is the electrode fro ...

sacrificial anode
" to act as the anode. The sacrificial metal instead of the protected metal, then, corrodes. A common application of cathodic protection is in
galvanized Galvanization or galvanizing ( also spelled galvanisation or galvanising) is the process of applying a protective zinc Zinc is a chemical element with the Symbol (chemistry), symbol Zn and atomic number 30. Zinc is a slightly brittle metal ...
steel, in which a sacrificial coating of zinc on steel parts protects them from rust. Oxidation is used in a wide variety of industries such as in the production of
cleaning products Cleaning is the process of removing unwanted substances, such as dirt, infectious agents, and other impurities, from an object or environment. Cleaning occurs in many different contexts, and uses many different methods. Several occupations are de ...
and oxidizing
ammonia Ammonia is a compound Compound may refer to: Architecture and built environments * Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall ** Compound (fortification), a version of the above fort ...

ammonia
to produce
nitric acid Nitric acid (), also known as ''aqua fortis'' (Latin for "strong water") and spirit of niter, is a highly corrosive mineral acid. The pure compound is colorless, but older samples tend to acquire a yellow cast due to decomposition into nitroge ...

nitric acid
. Redox reactions are the foundation of
electrochemical cell An electrochemical cell is a device capable of either generating electrical energy Electrical energy is energy derived from electric potential energy or kinetic energy. When used loosely, ''electrical energy'' refers to energy that has been c ...
s, which can generate electrical energy or support electrosynthesis. Metal
ore ore – psilomelane Psilomelane is a group name for hard black manganese oxides including hollandite and romanechite. Psilomelane consists of hydrous manganese Manganese is a chemical element Image:Simple Periodic Table Chart- ...

ore
s often contain metals in oxidized states such as oxides or sulfides, from which the pure metals are extracted by
smelting Smelting is a process of applying heat to ore in order to extract a base metal. It is a form of extractive metallurgy. It is used to extract many metals from their ores, including Silver mining#Ore processing, silver, iron-making, iron, copper ...
at high temperature in the presence of a reducing agent. The process of
electroplating Electroplating is a general name for processes that produce a metal coating on a solid substrate through the redox, reduction of cations of that metal by means of a direct current, direct electric current. The part to be coated acts as the cathode ...
uses redox reactions to coat objects with a thin layer of a material, as in chrome-plated parts,
silver plating Plating is a surface covering in which a metal is deposited on a conductive surface. Plating has been done for hundreds of years; it is also critical for modern technology. Plating is used to decorate objects, for corrosion inhibition, to improve ...
cutlery Cutlery includes any hand implement used in preparing, serving, and especially eating food Food is any substance consumed to provide Nutrient, nutritional support for an organism. Food is usually of plant, animal or Fungus, fungal origin, a ...

cutlery
,
galvanization Galvanization or galvanizing ( also spelled galvanisation or galvanising) is the process of applying a protective zinc Zinc is a chemical element with the Symbol (chemistry), symbol Zn and atomic number 30. Zinc is a slightly brittle metal ...
and gold-plated
jewelry Jewellery or jewelry consists of decorative items worn for personal adornment 150px, The principal adornment of these girls from the Bundu tribe in Sierra Leone is the adornment of bodies and faces with markings produced by the smearing on by ...

jewelry
.


Redox reactions in biology

Top:
ascorbic acid Vitamin C (also known as ascorbic acid and ascorbate) is a vitamin A vitamin is an organic molecule , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carb ...

ascorbic acid
(
reduced formIn statistics Statistics is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of data. In applying statistics to a scientific, industrial, or social problem, it is conventional to begin with a ...
of
Vitamin C Vitamin C (also known as ascorbic acid and ascorbate) is a vitamin found in various foods and sold as a dietary supplement. It is used to prevent and treat scurvy. Vitamin C is an Nutrient#Essential nutrients, essential nutrient involved in t ...

Vitamin C
)
Bottom:
dehydroascorbic acid Dehydroascorbic acid (DHA) is an oxidized form of ascorbic acid Vitamin C (also known as ascorbic acid and ascorbate) is a vitamin A vitamin is an organic molecule (or a set of molecules closely related chemically, i.e. vitamers) tha ...

dehydroascorbic acid
( of
Vitamin C Vitamin C (also known as ascorbic acid and ascorbate) is a vitamin found in various foods and sold as a dietary supplement. It is used to prevent and treat scurvy. Vitamin C is an Nutrient#Essential nutrients, essential nutrient involved in t ...

Vitamin C
)
Many important
biological Biology is the natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowl ...

biological
processes involve redox reactions. Before some of these processes can begin iron must be assimilated from the environment.
Cellular respiration upright=2.5, Typical eukaryotic cell Cellular respiration is a set of metabolic Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities ...

Cellular respiration
, for instance, is the oxidation of
glucose Glucose is a simple with the . Glucose is the most abundant , a subcategory of s. Glucose is mainly made by and most during from water and carbon dioxide, using energy from sunlight, where it is used to make in s, the most abundant carbohydr ...

glucose
(C6H12O6) to and the reduction of
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
to
water Water (chemical formula H2O) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known li ...

water
. The summary equation for cell respiration is: : C6H12O6 + 6 O2 → 6 CO2 + 6 H2O The process of cell respiration also depends heavily on the reduction of NAD+ to NADH and the reverse reaction (the oxidation of NADH to NAD+).
Photosynthesis Photosynthesis is a process used by plants and other organisms to into that, through , can later be released to fuel the organism's activities. Some of this chemical energy is stored in molecules, such as s and es, which are synthesized fro ...

Photosynthesis
and cellular respiration are complementary, but photosynthesis is not the reverse of the redox reaction in cell respiration: : 6 CO2 + 6 H2O +
light energy Light or visible light is electromagnetic radiation In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies ...

light energy
→ C6H12O6 + 6 O2 Biological energy is frequently stored and released by means of redox reactions. Photosynthesis involves the reduction of
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
into
sugar Sugar is the generic name for sweet-tasting, soluble carbohydrate is a disaccharide A disaccharide (also called a double sugar or ''biose'') is the sugar formed when two monosaccharides are joined by glycosidic linkage. Like monosacc ...

sugar
s and the oxidation of
water Water (chemical formula H2O) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known li ...
into molecular oxygen. The reverse reaction, respiration, oxidizes sugars to produce carbon dioxide and water. As intermediate steps, the reduced carbon compounds are used to reduce
nicotinamide adenine dinucleotide Nicotinamide adenine dinucleotide (NAD) is a coenzyme A cofactor is a non-protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains of amino acid residue (biochemistry), residues. Proteins pe ...
(NAD+) to NADH, which then contributes to the creation of a
proton gradient An electrochemical gradient is a gradient In vector calculus, the gradient of a scalar-valued function, scalar-valued differentiable function of Function of several variables, several variables is the vector field (or vector-valued function) \ ...
, which drives the synthesis of
adenosine triphosphate Adenosine triphosphate (ATP) is an organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properti ...

adenosine triphosphate
(ATP) and is maintained by the reduction of oxygen. In animal cells,
mitochondria A mitochondrion (; ) is a double-membrane Image:Schematic size.jpg, up150px, Schematic of size-based membrane exclusion A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, i ...

mitochondria
perform similar functions. See the ''
Membrane potential Membrane potential (also transmembrane potential or membrane voltage) is the difference in electric potential The electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is the amount of wo ...

Membrane potential
'' article.
Free radical A daughter category of ''Ageing'', this category deals only with the biological aspects of ageing. Ageing Ailments of unknown cause Biogerontology Biological processes Causes of death Cellular processes Gerontology Life extension Metabo ...
reactions are redox reactions that occur as a part of
homeostasis In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanis ...
and killing microorganisms, where an electron detaches from a molecule and then reattaches almost instantaneously. Free radicals are a part of redox molecules and can become harmful to the human body if they do not reattach to the redox molecule or an
antioxidant Antioxidants are that inhibit , a that can produce and s that may damage the of organisms. Antioxidants such as s or (vitamin C) may act to inhibit these reactions. To balance , plants and animals maintain complex systems of overlapping an ...

antioxidant
. Unsatisfied free radicals can spur the mutation of cells they encounter and are, thus, causes of cancer. The term ''redox state'' is often used to describe the balance of , NAD+/NADH and NADP+/NADPH in a biological system such as a cell or organ. The redox state is reflected in the balance of several sets of metabolites (e.g., and
pyruvate Pyruvic acid (CH3COCOOH) is the simplest of the alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate acid, conjugate base, CH3COCOO−, is a key intermediate in several metabolic pathways throughout the c ...

pyruvate
, , and
acetoacetate Acetoacetic acid (also acetoacetate and diacetic acid) is the organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound ...
), whose interconversion is dependent on these ratios. An abnormal redox state can develop in a variety of deleterious situations, such as hypoxia, shock, and
sepsis Sepsis is a life-threatening condition that arises when the body's response to infection An infection is the invasion of an organism's body Tissue (biology), tissues by Pathogen, disease-causing agents, their multiplication, and the reaction ...
. Redox mechanism also control some cellular processes. Redox proteins and their genes must be co-located for redox regulation according to the CoRR hypothesis for the function of DNA in mitochondria and chloroplasts.


Redox cycling

Wide varieties of
aromatic compounds Aromatic compounds are those chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held toget ...
are
enzymatically Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates int ...

enzymatically
reduced to form
free radicals In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they un ...
that contain one more electron than their parent compounds. In general, the electron donor is any of a wide variety of flavoenzymes and their
coenzyme A cofactor is a non-protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including ...
s. Once formed, these anion free radicals reduce molecular oxygen to
superoxide A superoxide is a compound that contains the superoxide ion, which has the chemical formula . The systematic name of the anion is dioxide(1−). The reactive oxygen ion superoxide is particularly important as the product of the one-electron ...

superoxide
and regenerate the unchanged parent compound. The net reaction is the oxidation of the flavoenzyme's coenzymes and the reduction of molecular oxygen to form superoxide. This catalytic behavior has been described as a
futile cycle A futile cycle, also known as a substrate cycle, occurs when two metabolic pathways run simultaneously in opposite directions and have no overall effect other than to dissipation, dissipate energy in the form of heat. The reason this cycle was call ...
or redox cycling.


Redox reactions in geology

In geology, redox is important to both the formation of minerals and the mobilization of minerals, and is also important in some depositional environments. In general, the redox state of most rocks can be seen in the color of the rock. The rock forms in oxidizing conditions, giving it a red color. It is then "bleached" to a green—or sometimes white—form when a reducing fluid passes through the rock. The reduced fluid can also carry uranium-bearing uranium ore deposits#Uranium minerals, minerals. Famous examples of redox conditions affecting geological processes include Uranium mining, uranium deposits and Navajo Sandstone#Iron oxide concretions (Moqui marbles), Moqui marbles.


Redox reactions in soils

Electron transfer reactions are central to myriad processes and properties in soils, and electron "activity", quantified as Eh (platinum electrode potential (voltage) relative to the standard hydrogen electrode) or pe (analogous to pH as -log electron activity, is a master variable, along with pH, that controls and is governed by chemical reactions and biological processes. Early theoretical research with applications to flooded soils and paddy rice production was seminal for subsequent work on thermodynamic aspects of redox and plant root growth in soils. Later work built on this foundation, and expanded it for understanding redox reactions related to heavy metal oxidation state changes, pedogenesis and morphology, organic compound degradation and formation, free radical chemistry, wetland delineation, soil remediation, and various methodological approaches for characterizing the redox status of soils.


Balancing redox reactions

Describing the overall electrochemical reaction for a redox process requires a ''balancing'' of the component
half-reaction A half reaction (or half-cell reaction) is either the oxidation or reduction reaction component of a redox (mild reducing agent) are added to powdered potassium permanganate Potassium permanganate is an inorganic compound with the chemical ...
s for oxidation and reduction. In general, for reactions in aqueous solution, this involves adding Proton, H+, Hydroxide, OH, Water (molecule), H2O, and electrons to compensate for the oxidation changes.


Acidic media

In acidic aqueous media, H+ ions and water are added to half-reactions to balance the overall reaction. For instance, when manganese(II) reacts with sodium bismuthate: : The reaction is balanced by scaling the two half-cell reactions to involve the same number of electrons (multiplying the oxidation reaction by the number of electrons in the reduction step and vice versa): :8 H2O(l) + 2 Mn2+(aq) → 2 (aq) + 16 H+(aq) + 10 e :10 e + 30 H+ + 5 (s) → 5 Bi3+(aq) + 15 H2O(l) Adding these two reactions eliminates the electrons terms and yields the balanced reaction: :14 H+(aq) + 2 Mn2+(aq) + 5 NaBiO3(s) → 7 H2O(l) + 2 (aq) + 5 Bi3+(aq) + 5 (aq)


Basic media

In basic aqueous media, Hydroxide, OH ions and water are added to half-reactions to balance the overall reaction. For example, in the reaction between potassium permanganate and sodium sulfite: : Balancing the number of electrons in the two half-cell reactions gives: :6 e + 4 H2O + 2  → 2 MnO2 + 8 OH :6 OH + 3  → 3  + 3 H2O + 6 e Adding these two half-cell reactions together gives the balanced equation: :2 KMnO4 + 3 Na2SO3 + H2O → 2 MnO2 + 3 Na2SO4 + 2 KOH


Mnemonics

The key terms involved in redox are often confusing. For example, a reagent that is oxidized loses electrons; however, that reagent is referred to as the reducing agent. Likewise, a reagent that is reduced gains electrons and is referred to as the oxidizing agent. These mnemonics are commonly used by students to help memorise the terminology: * "Oil rig, OIL RIG" — oxidation is loss of electrons, reduction is gain of electrons * "LEO the lion says GER [grr]" — loss of electrons is oxidation, gain of electrons is reduction * "LEORA says GEROA" — the loss of electrons is called oxidation (reducing agent); the gain of electrons is called reduction (oxidizing agent). * "RED CAT" and "AN OX", or "AnOx RedCat" ("an ox-red cat") — reduction occurs at the cathode and the anode is for oxidation * "RED CAT gains what AN OX loses" – reduction at the cathode gains (electrons) what anode oxidation loses (electrons) * "PANIC" – Positive Anode and Negative is Cathode. This applies to electrolytic cells which release stored electricity, and can be recharged with electricity. PANIC does not apply to cells that can be recharged with redox materials. These galvanic cell, galvanic or voltaic cells, such as fuel cells, produce electricity from internal redox reactions. Here, the positive electrode is the cathode and the negative is the anode.


See also

* Anaerobic respiration * Bessemer process * Bioremediation * Calvin cycle * Chemical equation * Chemical looping combustion * Citric acid cycle * Electrochemical series * Electrochemistry * Electrolysis * Electron equivalent * Electron transport chain * Electrosynthesis * Galvanic cell * Hydrogenation *
Membrane potential Membrane potential (also transmembrane potential or membrane voltage) is the difference in electric potential The electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is the amount of wo ...

Membrane potential
* Microbial fuel cell * Murburn concept * Nucleophilic abstraction * Organic redox reaction * Oxidative addition, Oxidative addition and reductive elimination * Oxidative phosphorylation * Partial oxidation * Pro-oxidant * Redox gradient * Redox potential * Reducing agent * Reducing atmosphere * Reduction potential * Exothermic, Thermic reaction * Transmetalation * Sulfur cycle


References


Further reading

* *


External links


Chemical Equation Balancer
– An open-source chemical equation balancer that handles redox reactions.




Online redox reaction equation balancer, balances equations of any half-cell and full reactions
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