Redox reactions include all chemical processes in which atoms have their oxidation number (oxidation state) changed. A chemical reaction is a process involving one, two, or more substances, such as compounds or atoms. ... The oxidation state or oxidation number is defined as the sum of negative and positive charges in an atom, which indirectly indicates the number of electrons it has accepted or donated. ...

This can be a simple redox process, such as the combustion of carbon to yield carbon dioxide, it could be the reduction of carbon by hydrogen to yield methane, or it could be the oxidation of sugar in the human body, through a series of very complex electron transfer processes. Combustion or burning is an exothermic reaction between a substance (the fuel) and a gas (the oxidizer), usually O2, to release heat. ... General Name, Symbol, Number carbon, C, 6 Chemical series nonmetals Group, Period, Block 14, 2, p Appearance black (graphite) colorless (diamond) Atomic mass 12. ... Carbon dioxide is an atmospheric gas composed of one carbon and two oxygen atoms. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... R-phrases S-phrases , , , Flash point −188 °C Autoignition temperature 537 °C Explosive limits 5–15% Supplementary data page Structure and properties n, εr, etc. ...

The term redox comes from the two concepts of reduction and oxidation.

Oxidation describes the loss of an electron by a molecule, atom, or ion; loss of hydrogen, or gain of oxygen. It also means an increase in oxidation number.

Reduction describes the uptake of an electron by a molecule, atom, or ion; loss of oxygen and gain of hydrogen. It also means a decrease in oxidation number.

These two terms go together, because in a chemical reaction, one cannot occur without the other; electrons lost by one compound must be gained by another. Reduction can also be considered to be the reducing of an atom's positive charge, and oxidation its opposite (gaining positive charge). Properties The electron is a fundamental subatomic particle which carries a negative electric charge. ... A molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ... This article needs to be cleaned up to conform to a higher standard of quality. ... An ion is an atom or group of atoms with a net electric charge. ... General Name, Symbol, Number oxygen, O, 8 Chemical series nonmetals Group, Period, Block 16, 2, p Appearance colorless Atomic mass 15. ...

The rusting of iron

Download high resolution version (1600x1063, 274 KB) Wikipedia does not have an article with this exact name. ... Download high resolution version (1600x1063, 274 KB) Wikipedia does not have an article with this exact name. ...

Oxidizing and reducing agents

Substances that have the ability to oxidize (Commonwealth English oxidise) other substances are said to be oxidative and are known as oxidizing agents, oxidants or oxidizers. Put in another way, the oxidant removes electrons from the other substance, and is thus reduced itself. Oxidants are usually chemical substances with elements in high oxidation numbers (e.g. H₂O₂, MnO₄^-, CrO₃, Cr₂O₇^2-, OsO₄) or highly electronegative substances that can gain one or two extra electrons by oxidizing a substance (O₂, O₃, F₂, Cl₂, Br₂). Hydrogen peroxide (H2O2) is a clear liquid, slightly more viscous than water, that has strong oxidizing properties and is therefore a powerful bleaching agent that has found use as a disinfectant, as an oxidizer, and (particularly in high concentrations as high test peroxide (HTP)) as a monopropellant in rockets. ... Electronegativity is the measure of the ability of an atom or molecule to attract electrons in the context of a chemical bond. ... General Name, Symbol, Number oxygen, O, 8 Chemical series nonmetals Group, Period, Block 16, 2, p Appearance colorless Atomic mass 15. ... Ozone (O3) is an allotrope of oxygen, the molecule consisting of three oxygen atoms instead of the more stable diatomic O2. ... General Name, Symbol, Number fluorine, F, 9 Chemical series halogens Group, Period, Block 17, 2, p Appearance pale greenish-yellow gas Atomic mass 18. ... General Name, Symbol, Number chlorine, Cl, 17 Chemical series halogens Group, Period, Block 17, 3, p Appearance yellowish green Atomic mass 35. ... General Name, Symbol, Number bromine, Br, 35 Chemical series halogens Group, Period, Block 17, 4, p Appearance gas/liquid: red-brown solid: metallic luster Atomic mass 79. ...

Substances that have the ability to reduce other substances are said to be reductive and are known as reductive agents, reductants, or reducers. Put in another way, the reductant transfers electrons to the substance. Reductants in chemistry are very diverse. Metal reduction - electropositive elemental metals can be used (Li, Na, Mg, Fe, Zn, Al). These metals donate or give away electrons readily. Other kinds of reductants are hydride transfer reagents (NaBH₄, LiAlH₄), these reagents are widely used in organic chemistry, primarily in the reduction of carbonyl compounds to alcohols. Another useful method is reductions involving hydrogen gas (H₂) with a palladium, platinum, or nickel catalyst. These catalytic reductions are primarily used in the reduction of carbon-carbon double or triple bonds. Hot metal work from a blacksmith In chemistry, a metal (Greek: Metallon) is an element that readily forms ions (cations) and has metallic bonds, and metals are sometimes described as a lattice of positive ions (cations) in a cloud of electrons. ... Organic chemistry is the scientific study of the structure, properties, composition, reactions, and synthesis of organic compounds that by definition contain carbon. ... In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom. ... In general usage, alcohol (from Arabic al-khwl الكحول, or al-ghawl الغول) refers almost always to ethanol, also known as grain alcohol, and often to any beverage that contains ethanol (see alcoholic beverage). ... General Name, Symbol, Number palladium, Pd, 46 Chemical series transition metals Group, Period, Block 10, 5, d Appearance silvery white metallic Atomic mass 106. ... General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Atomic mass 195. ... General Name, Symbol, Number nickel, Ni, 28 Chemical series transition metals Group, Period, Block 10, 4, d Appearance lustrous, metallic Atomic mass 58. ... A catalyst (Greek: καταλύτης, catalytÄ“s) is a substance that accelerates the rate (speed) of a chemical reaction without itself being transformed or consumed by the reaction (see also catalysis). ...

The chemical way to look at redox processes is that the reductant transfers electrons to the oxidant. Thus, at the end of the reaction, the reductant will have been oxidized and the oxidant will have been reduced.

Former meaning (oxygen/hydrogen)

Formerly, oxidation simply meant the addition of oxygen or the removing of hydrogen (hence the name oxidation), and reduction was removal of oxygen or the addition of hydrogen. Currently, however, the terms are normally used in a more general sense, describing electron movement. General Name, Symbol, Number oxygen, O, 8 Chemical series nonmetals Group, Period, Block 16, 2, p Appearance colorless Atomic mass 15. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ...

Examples of redox reactions

A good example is the reaction between hydrogen and fluorine: General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... General Name, Symbol, Number fluorine, F, 9 Chemical series halogens Group, Period, Block 17, 2, p Appearance pale greenish-yellow gas Atomic mass 18. ...

H₂ + F₂ → 2HF

We can write this overall reaction as two half-reactions: an oxidation reaction:

H₂ → 2H⁺ + 2e^-

and a reduction reaction:

F₂ + 2e^- → 2F^-

Elements always have an oxidation number of zero. In the first half reaction hydrogen is oxidized from an oxidation number of zero to an oxidation number of +1. In the second half reaction fluorine is reduced from an oxidation number of zero to an oxidation number of −1.

When adding the reactions together the electrons cancel:

H₂ → 2H⁺ + 2e^-

+ 2e^- + F₂ → 2F^-

---------------------

H₂ + F₂ → 2H⁺ + 2F^-

And the ions combine to form hydrogen fluoride:

2H⁺ + 2F^- → 2HF

Other examples

• iron(II) oxidizes to iron(III):

Fe²⁺ → Fe³⁺ + e^-

• hydrogen peroxide reduces to hydroxide:

H₂O₂ + 2 e^- → 2 OH^-

overall equation for the above: Hydrogen peroxide (H2O2) is a clear liquid, slightly more viscous than water, that has strong oxidizing properties and is therefore a powerful bleaching agent that has found use as a disinfectant, as an oxidizer, and (particularly in high concentrations as high test peroxide (HTP)) as a monopropellant in rockets. ... Hydroxide is a polyatomic ion consisting of oxygen and hydrogen: −O−H It has a charge of −1. ...

2Fe²⁺ + H₂O₂ + 2H⁺ → 2Fe³⁺ + 2H₂O

• denitrification, nitrate reduces to nitrogen:

2NO₃^- + 10e^- + 12 H⁺ → N₂ + 6H₂O

• iron oxidizes to iron(III) oxide and oxygen is reduced forming iron(III) oxide (commonly known as rusting or tarnishing):

4Fe + 3O₂ → 2 Fe₂O₃.

• Combustion of hydrocarbons produces water, carbon dioxide, some partially oxidized forms such as carbon monoxide, and heat energy. Complete oxidation of materials containing carbon produces carbon dioxide.

• In organic chemistry, stepwise oxidation of a hydrocarbon produces water and, successively, an alcohol, an aldehyde or a ketone, carboxylic acid, and then a peroxide.

Denitrification is the process of reducing nitrate, a form of nitrogen available for consumption by many groups of organisms, into gaseous nitrogen, which is far less accessible to life forms but makes up the bulk of our atmosphere. ... this is a negative ion,NO3- Discussion In inorganic chemistry, nitrates are the salts of nitric acid. ... General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless Atomic mass 14. ... Rusted cars The rusting can completely eat away iron Rusted bolt A blacksmith removing rust with sand prior to welding Rust is the substance formed when iron compounds corrode in the presence of water and oxygen. ... Tarnish is a layer of corrosion that develops over copper, brass, silver, or aluminum as they undergo oxidation. ... Combustion or burning is an exothermic reaction between a substance (the fuel) and a gas (the oxidizer), usually O2, to release heat. ... // Definition In chemistry, a hydrocarbon is any chemical compound that consists only of the elements carbon (C) and hydrogen (H). ... Water (from the Old English word wæter; c. ... Carbon dioxide is an atmospheric gas composed of one carbon and two oxygen atoms. ... Carbon monoxide, chemical formula CO, is a colourless, odourless, flammable and highly toxic gas. ... General Name, Symbol, Number carbon, C, 6 Chemical series nonmetals Group, Period, Block 14, 2, p Appearance black (graphite) colorless (diamond) Atomic mass 12. ... Organic chemistry is the scientific study of the structure, properties, composition, reactions, and synthesis of organic compounds that by definition contain carbon. ... In general usage, alcohol (from Arabic al-ghawl الغول) refers almost always to ethanol, also known as grain alcohol, and often to any beverage that contains ethanol (see alcoholic beverage). ... An aldehyde is either a functional group consisting of a terminal carbonyl group, or a compound containing a terminal carbonyl group. ... A ketone is either the functional group characterized by a carbonyl group linked to two other carbon atoms or a compound that contains this functional group. ... Structure of a carboxylic acid Carboxylic acids are organic acids characterized by the presence of a carboxyl group, which has the formula -C(=O)-OH, usually written as COOH. The salts and anions of carboxylic acids are called carboxylates generally. ... Peroxide has three distinct meanings: // Colloquial meaning In common usage, peroxide is an aqueous solution of hydrogen peroxide (HOOH or H2O2) sold for use as a disinfectant or mild bleach. ...

Redox reactions in biology

Much biological energy is stored and released by means of redox reactions. Photosynthesis involves 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. As intermediate steps, the reduced carbon compounds are used to reduce nicotinamide adenine dinucleotide (NAD⁺), which then contributes to the creation of a proton gradient, which drives the synthesis of adenosine triphosphate (ATP) and is maintained by the reduction of oxygen. In animal cells, mitochondria perform similar functions. See Membrane potential article. Main articles: Life The most salient example of biological universality is that all living things share a common carbon-based biochemistry and in particular pass on their characteristics via genetic material, which is based on nucleic acids such as DNA and which uses a common genetic code with only minor... Leaf. ... Carbon dioxide is an atmospheric gas composed of one carbon and two oxygen atoms. ... In general use, sugar is taken to mean sucrose, also called table sugar or saccharose, a disaccharide which is a white crystalline solid. ... Water has the chemical formula H2O, meaning that one molecule of water is composed of two hydrogen atoms and one oxygen atom. ... General Name, Symbol, Number oxygen, O, 8 Chemical series nonmetals Group, Period, Block 16, 2, p Appearance colorless Atomic mass 15. ... Cellular respiration is the process in which the chemical bonds of energy-rich molecules such as glucose are converted into energy usable for life processes. ... Nicotinamide adenine dinucleotide (NAD+) (Note that the adenonosyl sugar is of the wrong absolute configuration in the diagram: it should have the same configuration as the nicotinamide sugar. ... An ion gradient is a concentration gradient of ions, it can be called an electrochemical potential gradient of ions across membranes. ... Adenosine 5-triphosphate (ATP) is the nucleotide known in biochemistry as the molecular currency of intracellular energy transfer; that is, ATP is able to store and transport chemical energy within cells. ... In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. ... Membrane potential (or transmembrane potential or transmembrane potential difference or transmembrane potential gradient), is the electrical potential difference (voltage) across a cells plasma membrane. ...

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., lactate and pyruvate, beta-hydroxybutyrate and acetoacetate) 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. Lactic acid is a chemical compound that plays a role in several biochemical processes. ... Pyruvate (CH3COCOO−) is the ionized form of pyruvic acid. ... Acetoacetic acid (also known as 3-oxobutanoic acid or diacetic acid) is a beta-keto acid of the keto acid group, its empirical formula is C4H6O3 or CH3COCH2COOH. It is a strong organic acid and can be produced in the human liver under certain conditions of poor metabolism leading to... Hypoxia has several meanings: Hypoxia is the lack of oxygen in tissues, see Hypoxia (medical) Hypoxia is the lack of oxygen in a water body leading to the death of organisms, see Hypoxia (water) This is a disambiguation page — a navigational aid which lists other pages that might otherwise share... In medicine, shock (hypoperfusion) is a life-threatening medical emergency characterized by inability of the body to supply enough oxygen to meet tissue requirements. ... Sepsis (in Greek Σήψις, putrefaction) is a serious medical condition caused by a severe infection leading to a systemic inflammatory response. ...

See also

• Bioremediation
• Calvin cycle
• Citric acid cycle
• Electrochemical cell
• Electrochemistry
• Galvanic cell
• Membrane potential
• Thermic reaction

Bioremediation can be defined as any process that uses microorganisms or their enzymes to return the environment altered by contaminants to its original condition. ... The Calvin cycle (also known as Calvin-Benson cycle) is a series of biochemical reactions taking place in the chloroplasts of photosynthetic organisms. ... The citric acid cycle (also known as the tricarboxylic acid cycle, the TCA cycle, or the Krebs cycle) is a series of chemical reactions of central importance in all living cells that utilize oxygen as part of cellular respiration. ... An electrochemical cell is a setup used for creating an electromotive force(voltage) in a conductor separating two reactions. ... Electrochemistry is the science of the reactions that can take place at the interface of an electronic conductor (the electrode, which can be a metal or a semiconductor including graphite) and an ionic conductor (the electrolyte). ... The Galvanic cell, named after Luigi Galvani, consists of two metals connected by an electrolyte which forms a salt bridge between the metals. ... Membrane potential (or transmembrane potential or transmembrane potential difference or transmembrane potential gradient), is the electrical potential difference (voltage) across a cells plasma membrane. ... Thermic reactions are chemical reactions which are thermic: either highly exothermic (producing heat) or endothermic (absorbing heat). ...

External links

• Redox Reactions Calculator
• Redox reactions at Chemguide