The most fundamental reactions in chemistry are the redox processes. The term redox process accounts for all processes in which atoms have their oxidation number (oxidation state) changed. This can be a simple redox process, such as the combustion of carbon by oxygen 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, to yield water and carbon dioxide.

The term redox comes from the two concepts of reduction and oxidation. Reduction describes the uptake of an electron by a molecule or atom. Oxidation describes the loss of an electron by a molecule or atom. 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.

Oxidizing and Reducing agents

Substances that have the ability to oxidize 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 substance. Oxidants are usually chemical substances in high oxidation numbers (eg. The chemical compound hydrogen peroxide (H2O2) is a viscous liquid that has strong oxidizing properties and is therefore a powerful bleaching agent that has found use as a disinfectant and (in high concentrations) as an oxidizer or monopropellant in rockets. Hydrogen peroxide is manufactured commercially by several processes. Inorganic processes... H₂O₂, MnO₄^-, CrO₃, OsO₄) or very electronegative substances that can gain one or two extra electrons by oxidizing a substance ( General Name, Symbol, Number Oxygen, O, 8 Chemical series nonmetals Group, Period, Block 16 (VIA), 2, p Density, Hardness 1.429 kg/m3, NA Appearance colorless Atomic properties Atomic weight 15.9994 g/mol Atomic radius (calc.) 60 (48) pm Covalent radius 73 pm van der Waals radius 152 pm... O₂, O₃, General Name, Symbol, Number Fluorine, F, 9 Series Halogens Group, Period, Block 17 (VIIA), 2 , p Density, Hardness 1.696 kg/m3, NA Appearance pale greenish-yellow gas Atomic properties Atomic weight 18.9984 g/mol Atomic radius (calc.) 50 (42) pm Covalent radius 71 pm van der Waals radius... F₂, General Name, Symbol, Number chlorine, Cl, 17 Series halogens Group, Period, Block 17 (VIIA), 3, p Density, Hardness 3.214 kg/m3 (273 K), NA Appearance yellowish green Atomic properties Atomic weight 35.453 amu Atomic radius (calc.) 100 pm (79) pm Covalent radius 99 pm van der Waals radius... Cl₂, General Name, Symbol, Number bromine, Br, 35 Series halogens Group, Period, Block 17 (VIIA), 4, p Density, Hardness 3119 kg/m3 (300 K), NA Appearance Gas: red-brown solid: metallic luster Atomic properties Atomic weight 79.904 amu Atomic radius (calc.) 115 (94) pm Covalent radius 114 pm van der... Br₂)

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 are very eager to give away electrons. Other kinds of reductants are hydride transfer reagents (NaBH₄, LiAlH₄), these reagents are widely used in organic chemistry, primarily in the reduction of In chemistry, a carbonyl group is a functional group composed of an atom of carbon double-bonded to an atom of oxygen. It is the functional group present in aldehydes (where it is located terminally) and ketones (internally), and forms the basis for several other functional groups, such as those... carbonyl compounds to 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). This sense underlies the term alcoholism (addiction... alcohols. Another useful method is reductions involving hydrogen gas (H₂) with a palladium, platinium or nickel catalyst. These catalytic reductions are primarily used in the reduction of carbon-carbon double or triple bonds.

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. This does not mean however, that the reverse process takes place (because that would lead to status quo), but it does often lead to equilibrium.

Chemistry students sometimes remember the nature of oxidation and reduction using the simple A mnemonic (AmE [] or BrE []) is a memory aid. Mnemonics are often verbal, are sometimes in verse form, and are often used to remember lists. Mnemonics rely not only on repetition to remember facts, but also on creating associations among easy-to-remember constructs and lists of data. The word... mnemonic device "LEO says GER" - the Loss of Electrons is Oxidation, while the Gain of Electrons is Reduction. Another is "OIL RIG" - Oxidation Is Loss, Reduction Is Gain.

Former meaning (Oxygen/Hydrogen)

Formerly, smoke oxidation simply meant the addition of General Name, Symbol, Number Oxygen, O, 8 Chemical series nonmetals Group, Period, Block 16 (VIA), 2, p Density, Hardness 1.429 kg/m3, NA Appearance colorless Atomic properties Atomic weight 15.9994 g/mol Atomic radius (calc.) 60 (48) pm Covalent radius 73 pm van der Waals radius 152 pm... oxygen or the removing of General Name, Symbol, Number Hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1 (IA), 1 , s Density, Hardness 0.0899 kg/m3, NA Appearance colorless Atomic properties Atomic weight 1.00794 amu Atomic radius (calc) 25 (53) pm Covalent radius 37 pm van der Waals radius 120 pm Electron... hydrogen (hence the name oxidation), and smoke reduction was removal of oxygen or the addition of hydrogen. Currently, however, the terms are normally used in the more general sense.

Examples of redox reactions

A good example is the reaction between General Name, Symbol, Number Hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1 (IA), 1 , s Density, Hardness 0.0899 kg/m3, NA Appearance colorless Atomic properties Atomic weight 1.00794 amu Atomic radius (calc) 25 (53) pm Covalent radius 37 pm van der Waals radius 120 pm Electron... hydrogen and General Name, Symbol, Number Fluorine, F, 9 Series Halogens Group, Period, Block 17 (VIIA), 2 , p Density, Hardness 1.696 kg/m3, NA Appearance pale greenish-yellow gas Atomic properties Atomic weight 18.9984 g/mol Atomic radius (calc.) 50 (42) pm Covalent radius 71 pm van der Waals radius... fluorine:

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 Hydrofluoric acid is a highly corrosive solution of the chemical compound hydrogen fluoride in water. Pure hydrogen fluoride is often called anhydrous hydrofluoric acid. Paradoxically, though in chemical terms hydrofluoric acid is a weak acid, it has the unique ability to dissolve almost all inorganic oxides. As such, it must... hydrogen fluoride:

2H⁺ + 2F^- → 2HF

Other examples

• iron(II) oxidises/oxidizes to iron(III):

Fe²⁺ → Fe³⁺ + e^-

• The chemical compound hydrogen peroxide (H2O2) is a viscous liquid that has strong oxidizing properties and is therefore a powerful bleaching agent that has found use as a disinfectant and (in high concentrations) as an oxidizer or monopropellant in rockets. Hydrogen peroxide is manufactured commercially by several processes. Inorganic processes... hydrogen peroxide reduces to Hydroxide is a functional group consisting of oxygen and hydrogen: -O−H It has a charge of 1-. The term hydroxyl group is used when the functional group -OH is counted as a substituent of an organic compound. Organic molecules containing a hydroxyl group are known as alcohols (CnH2n... hydroxide:

H₂O₂ + 2 e^- → 2 OH^-

overall equation for the above:

2Fe²⁺ + H₂O₂ + 2H⁺ → 2Fe³⁺ + 2H₂O

• 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. It can be thought of as the opposite of nitrogen fixation, which... denitrification, Nitrates are the salts of nitric acid. The nitrate ion is the polyatomic ion with chemical formula NO3−; it is the conjugate base of nitric acid. The nitrate ion is planar and has the following structure: O O− / N+ | O− A nitrate salt forms if a positively... nitrate reduces to General Name, Symbol, Number Nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15 (VA), 2 , p Density 1.2506 kg/m3 Hardness NA Appearance colorless Atomic properties Atomic weight 14.0067 amu Atomic radius (calc.) 65 (56) pm Covalent radius 75 pm van der Waals radius 155 pm Electron... nitrogen:

2NO₃^- + 10e^- + 12 H⁺ → N₂ + 6H₂O

• iron(II) oxidises/oxidizes to and oxygen reduces to iron(III) oxide (commonly known as This article is about the type of corrosion. For the fungus, see rust (fungus). For the person, see Mathias Rust. For the town in Austria, see Rust, Austria. A rusty bolt on a bridge over a small stream Rust is the substance formed when iron compounds corrode in the presence... rusting or Tarnish is a layer of corrosion that develops over copper, brass, silver, or aluminum as they undergo oxidation. How to treat When Tarnish occurs, it is treated chemically, usually with strong acids. Many commercial products are dedicated specifically to this. How to prevent Most tarnishing is prevented by Tinning, a... tarnishing):

4Fe + 3O₂ → 2 Fe₂O₃.

• Burning of In chemistry, a hydrocarbon is a cleaning solution consisting only of carbon (C) and hydrogen (H). They all consist of a carbon backbone and atoms of hydrogen attached to that backbone. (Often the term is used as a shortened form of the term aliphatic hydrocarbon.) For example, methane (swamp gas... hydrocarbons to produce Drinking water This article focuses on water as we experience it every day. The water (molecule) article describes the water chemical and physical properties from a scientific and technical perspective. Water (from Low German or Old Saxon) is an abundant substance on Earth. It exists in many places and forms... water, Carbon dioxide is an atmospheric gas composed of one carbon and two oxygen atoms. A very widely known chemical compound, it is frequently called by its formula CO2. Carbon dioxide results from the combustion of organic matter if sufficient amounts of oxygen are present. It is also produced by various... carbon dioxide, some partially oxidized forms, and heat Energy is a fundamental quantity that every physical system possesses; it allows us to predict how much work the system could be made to do, or how much heat it can exchange. In the past, energy was discussed in terms of easily observable effects it has on the properties of... energy. Complete oxidation of materials containing General Name, Symbol, Number Carbon, C, 6 Chemical series Nonmetals Group, Period, Block 14 (IVA), 2, p Density, Hardness 2267 kg/m3 0.5 (graphite) 3516 - 3525 kg/m3 10.0 (diamond) Appearance black (graphite) colourless (diamond) Atomic properties Atomic mass 12.0107 u Atomic radius (calc.) 70 (67) pm... carbon produces Carbon dioxide is an atmospheric gas composed of one carbon and two oxygen atoms. A very widely known chemical compound, it is frequently called by its formula CO2. Carbon dioxide results from the combustion of organic matter if sufficient amounts of oxygen are present. It is also produced by various... carbon dioxide, which is linked to Global Mean Temperatures 1880-2005 Global warming is a term used to describe an increase over time of the average temperature of Earths atmosphere and oceans. Global warming theories attempt to account for the rise in average global temperatures since the late 19th century (0.6 ± 0.2°C... global warming because it absorbs certain The wavelength is the distance between repeating units of a wave pattern. It is commonly designated by the Greek letter lambda (λ). In a sine wave, the wavelength is the distance between peaks: The x axis represents distance, and I would be some varying quantity (for instance air pressure for... wavelengths of Image of a small dog taken in mid-infrared (thermal) light (false color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than visible light, but shorter than microwave radiation. The name means below red (from the Latin infra, below), red being the color of visible light of longest... infrared light.

• In Organic chemistry is the scientific study of the structure, properties, composition, reactions, and synthesis of organic compounds. History Organic chemistry as a science is generally agreed to have started in 1828 with Friedrich Woehlers synthesis of the organic, biologically significant compound urea by accidentally evaporating an aqueous solution of... organic chemistry, stepwise oxidation of a hydrocarbon produces water and, successively, an 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). This sense underlies the term alcoholism ( addiction... alcohol, an An aldehyde is either a functional group consisting of a terminal carbonyl group, or a compound containing a terminal carbonyl group. (Where -R represents the carbon chain.) Structure The aldehyde functional group is a carbonyl group bonded to a hydrogen atom and a carbon atom. α carbon & α hydrogen... aldehyde or a 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. A ketone can be generally represented by the formula: R1(CO)R2. A carbonyl carbon bonded to two carbon atoms distinguishes ketones from carboxylic... ketone, In chemistry, carboxylic acids (also called alkanoic acids) are organic acids characterized by the presence of a carboxyl group. Carboxylic acids thus have the structure where R is a hydrogen or an organic group. In chemical formulas, this is also written as RCOOH. Acidity, electron distribution and resonance Carboxylic acids... carboxylic acid, and then a 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. The usual peroxide of commerce is a dilute solution containing traces of stabilisers, and is sold in either brown glass... peroxide.

• In Inorganic chemistry is the branch of chemistry concerned with the properties and reactions of inorganic compounds. This includes all chemical compounds except the many which are based upon chains or rings of carbon atoms, which are termed organic compounds and are studied under the separate heading of organic chemistry. The... inorganic chemistry terms, incompletely oxidized General Name, Symbol, Number Carbon, C, 6 Chemical series Nonmetals Group, Period, Block 14 (IVA), 2, p Density, Hardness 2267 kg/m3 0.5 (graphite) 3516 - 3525 kg/m3 10.0 (diamond) Appearance black (graphite) colourless (diamond) Atomic properties Atomic mass 12.0107 u Atomic radius (calc.) 70 (67) pm... carbon takes the form of Carbonate is an anion with a charge of -2 and an empirical formula of CO32-. An aqueous solution of carbon dioxide contains a minute amount of H2CO3, called carbonic acid, which dissociates to form hydrogen ions and carbonate ions. It would be a fairly strong acid if carbonic acid existed... carbonate, Bicarbonate is a polyatomic ion whose formula is HCO3-. It is the intermediate form in the deprotonation of carbonic acid: removing the first proton from carbonic acid forms bicarbonate; removing the second proton leads to the carbonate ion. The salts which contain the bicarbonate ion are also known as bicarbonates... bicarbonate or Carbon monoxide, chemical formula CO, is a colourless, odourless, flammable and highly toxic gas. It is a major product of the incomplete combustion of carbon and carbon-containing compounds. Sources Carbon monoxide has many common sources. The exhaust of the internal combustion engine, when burning a carbon-based fuel (i... carbon monoxide.

Redox reactions in biology

Much Biology studies the variety of life (clockwise from top-left) E. coli, tree fern, gazelle, Goliath beetle Biology is the science of life (from the Greek words bios = life and logos = word). It is concerned with the characteristics and behaviors of organisms, how species and individuals come into existence, and... biological energy is stored and released by means of redox reactions. Leaf. The primary site of photosynthesis in plants. Photosynthesis is a biochemical process in which plants, algae, and some bacteria harness the energy of light to produce food. Ultimately, nearly all living things depend on energy produced from photosynthesis for their nourishment, making it vital to life on Earth. It... Photosynthesis involves the reduction of Carbon dioxide is an atmospheric gas composed of one carbon and two oxygen atoms. A very widely known chemical compound, it is frequently called by its formula CO2. Carbon dioxide results from the combustion of organic matter if sufficient amounts of oxygen are present. It is also produced by various... carbon dioxide into This article deals with sugar as food and as an important, widely traded commodity; the word also has other uses; see Sugar (disambiguation) A sugar is a form of carbohydrate; the most commonly used sugar is a white crystalline solid, sucrose; used to alter the flavor and properties (mouthfeel, perservation... sugars and the oxidation of This article describes water from a scientific and technical perspective. See the water article for its importance for life and mankind. Water is liquid at standard temperature and pressure. It has the chemical formula H2O, meaning that one molecule of water is composed of two hydrogen atoms and one oxygen... water into molecular General Name, Symbol, Number Oxygen, O, 8 Chemical series nonmetals Group, Period, Block 16 (VIA), 2, p Density, Hardness 1.429 kg/m3, NA Appearance colorless Atomic properties Atomic weight 15.9994 g/mol Atomic radius (calc.) 60 (48) pm Covalent radius 73 pm van der Waals radius 152 pm... oxygen. The reverse reaction, Respiration can refer to: Cellular respiration, which is the use of oxygen in the metabolism of organic molecules. Physiological respiration, which exchanges oxygen and carbon dioxide between an organism and the external environment. This is a disambiguation page — a navigational aid which lists other pages that might otherwise share... respiration, oxidises/oxidizes sugars to produce carbon dioxide and water. As intermediate steps, the reduced carbon compounds are used to reduce Nicotinamide adenine dinucleotide (NAD+) Nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) are two important coenzymes found in cells. NADH is the reduced form and NAD+ is the oxidized form of NAD. NAD is used extensively in glycolysis and the citric acid cycle of cellular respiration. It forms... Nicotinamide adenine dinucleotide (NAD⁺), which then contributes to the creation of a An ion gradient is a concentration gradient of ions, it can be called an electrochemical potential gradient of ions across membranes. Ionophores are important for ion gradients. The chemiosmotic potential is used as energy storage, chemiosmotic coupling is one of several ways a thermodynamically unfavorable reaction can be driven by... proton gradient, which drives the synthesis of For other uses of the initials ATP, see ATP (disambiguation) Adenosine triphosphate (ATP) Adenosine triphosphate (ATP) is the nucleotide known in biochemistry as the energy transfer; that is, ATP is able to store and transport chemical energy within cells. ATP also plays an important role in the synthesis of nucleic... Adenosine triphosphate (ATP) and is maintained by the reduction of oxygen.

In animal cells, In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. Mitochondria are sometimes described as cellular power plants because their primary purpose is to manufacture adenosine triphosphate (ATP), which is used as a source of energy. The number of mitochondria found in different types of... mitochondria perform similar functions.

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., Lactic acid is a chemical compound that plays a role in several biochemical processes. It is the acid that gives old milk its sour taste, and it accumulates in skeletal muscles during extensive anaerobic exercise, causing temporary muscle pain. Lactic acid is quickly removed from muscles when they resume aerobic... lactate and Pyruvate (CH3COCOO−) is the ionized form of pyruvic acid. It is an important chemical compound in biochemistry. It is the output of the breakdown of glucose known as glycolysis, and (in aerobic respiration) the main input for the citric acid cycle. In anaerobic respiration, pyruvate from glycolysis can be... pyruvate, beta-hydroxybutyrate and 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... acetoacetate) whose interconversion is dependent on these ratios. An abnormal redox state can develop in a variety of deleterious situations, such as 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... hypoxia, This article is about medicine. See also electric shock. For the concept of shock in physics and mechanics, see Shock (mechanics). For the 1946 film noir starring Vincent Price, see Shock (movie) In medicine, shock is a life-threatening medical emergency characterized by inability of the body to supply enough... shock, and Sepsis (in Greek Σήψις) is a serious medical condition caused by a severe systemic infection leading to a systemic inflammatory response. The more critical subsets of sepsis include severe sepsis (sepsis with organ dysfunction) and septic shock (sepsis with refractory arterial hypotension). The systemic inflammatory response... sepsis.

See also

• Bioremediation can be defined as any process that uses microorganisms or their enzymes to return the environment altered by contaminants to its original condition. Bioremediation may be employed in order to attack specific contaminants, such as chlorinated pesticides that are degraded by bacteria, or a more general approach may be... Bioremediation
• The Calvin cycle (also known as Calvin-Benson cycle) is a series of biochemical reactions taking place in the chloroplasts of photosynthetic organisms. It was discovered by Melvin Calvin and Andy Benson at the University of California, Berkeley. During photosynthesis, light energy has been converted into chemical energy stored in... Calvin cycle
• 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. In these aerobic organisms, the citric acid cycle is a metabolic... Citric acid cycle
• Electrochemistry is the study of the electronic and electrical aspects of chemical reactions. The elements involved in an electrochemical reaction are characterized by the number of electrons each has. The oxidation state of an ion is the number of electrons it has accepted or donated compared to its neutral state... Electrochemistry
• The Galvanic cell, named after Luigi Galvani, consists of two metals connected by an electrolyte which forms a salt bridge between the metals. In 1780, Luigi Galvani discovered that when two different metals (copper and zinc for example) were connected together and then both touched to different parts of a... Galvanic cell

External link

• Redox Reactions Calculator (http://www.shodor.org/UNChem/advanced/redox/redoxcalc.html)