Redox (shorthand for reduction-oxidation reaction) describes all chemical reactions A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, often coming about only after the input of some type of energy, viz. heat, light or electricity. Classically, chemical reactions encompass in which atoms have their oxidation number In coordination chemistry, the oxidation number of a central atom in a coordination compound is the charge that it would have if all the ligands were removed along with the electron pairs that were shared with the central atom . Imagine the central atom of a molecule being stripped of all its appendages, and the intervening electrons going with (oxidation state In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by integers, which can be positive, negative, or zero) changed. This can be either a simple redox process, such as the oxidation of carbon Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. There are three naturally occurring isotopes, with 12C and 13C being stable, while 14C is radioactive, decaying with a half-life of to yield carbon dioxide Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state. CO2 is a trace gas comprising 0.039% of the atmosphere (CO2) or the reduction of carbon by hydrogen Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of 1.00794 u (1.007825 u for Hydrogen-1), hydrogen is the lightest and most abundant chemical element, constituting roughly 75 % of the Universe's elemental mass. Stars in the main sequence are mainly composed of hydrogen in its to yield methane Methane is a chemical compound with the chemical formula CH4. It is the simplest alkane, and the principal component of natural gas. Methane's bond angles are 109.5 degrees. Burning methane in the presence of oxygen produces carbon dioxide and water. The relative abundance of methane makes it an attractive fuel. However, because it is a gas at (CH4), or a complex process such as the oxidation of sugar Sugar is an informal term for a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose characterized by a sweet flavor. In food, sugar almost exclusively refers to sucrose, which primarily comes from sugar cane and sugar beet. Other sugars are used in industrial food preparation, but are usually known by more specific(C6H12O6) in the human body through a series of complex electron transfer Electron transfer is the process by which an electron moves from one atom or molecule to another atom or molecule. ET is a mechanistic description of the thermodynamic concept of redox, wherein the oxidation states of both reaction partners change processes.
The term comes from the two concepts of reduction and oxidation. It can be explained in simple terms:
- Oxidation is the loss of electrons The electron is a subatomic particle carrying a negative electric charge. It has no known components or substructure, and therefore is believed to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton. The intrinsic angular momentum of the electron is a half integer value in units of ħ, which means that or an increase in oxidation state by a molecule A molecule is defined as an electrically neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds. Molecules are distinguished from polyatomic ions in this strict sense. In organic chemistry and biochemistry, the term molecule is used less strictly and also is applied to charged organic molecules, atom The atom is a basic unit of matter that consists of a dense, central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons . The electrons of an atom are bound to the nucleus by the electromagnetic force. Likewise, a group of atoms can remain, or ion An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge.
- Reduction is the gain of electrons or a decrease in oxidation state by a molecule, atom, or ion.
Though sufficient for many purposes, these descriptions are not precisely correct. Oxidation and reduction properly refer to a change in oxidation number — the actual transfer of electrons may never occur. Thus, oxidation is better defined as an increase in oxidation number, and reduction as a decrease in oxidation number. In practice, the transfer of electrons will always cause a change in oxidation number, 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 form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms, and other covalent bonds. In short, the attraction-to-repulsion stability that forms between atoms when they share electrons is known as covalent bonding bonds).
Non-redox reactions, which do not involve changes in formal charge In chemistry, a formal charge is the charge assigned to an atom in a molecule, assuming that electrons in a chemical bond are shared equally between atoms, regardless of relative electronegativity, are known as metathesis Metathesis is a molecular process involving the exchange of bonds between the two reacting chemical species, which results in the creation of products with similar or identical bonding affiliations. This is represented by the general reaction scheme: reactions.
The two parts of a redox reaction Rusting Rust is a general term for a series of iron oxides. Colloquially, the term is applied to red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture. Yet, there are also other forms of rust, such as the result of the reaction of iron and chlorine in an environment deprived of oxygen, such as rebar used in iron A bonfire Fire is the rapid oxidation of a material in the chemical process of combustion, releasing heat, light, and various reaction products. Slower oxidative processes like rusting or digestion are not included by this definition. Combustion Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame. Fuels of interest often include organic compounds in the gas, liquid or consists of redox reactions involving free radicals In chemistry, radicals are atoms, molecules, or ions with unpaired electrons on an open shell configuration. Radicals may have positive, negative or zero charge. By convention, metals and their ions or complexes with unpaired electrons are not radicals. The unpaired electrons cause radicals to be highly chemically reactive.
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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 are involved in a particular reaction is called a redox pair.
Oxidizers
Substances that have the ability to oxidize other substances are said to be oxidative and are known as oxidizing agents In the above equation, the iron has an oxidation number of 0 before and 3+ after the reaction. For oxygen (O) the oxidation number began as 0 and decreased to 2−. These changes can be viewed as two "half-reactions" that occur concurrently:, oxidants, or oxidizers. Put another way, the oxidant removes electrons from another substance, and is thus itself reduced. And, because it "accepts" electrons, it is also called an electron acceptor An electron acceptor is a chemical entity that accepts electrons transferred to it from another compound. It is an oxidizing agent that, by virtue of its accepting electrons, is itself reduced in the process.
Oxidants are usually chemical elements or substances with elements in high oxidation numbers (e.g., H2O2 Hydrogen peroxide is naturally produced in organisms as a by-product of oxidative metabolism. Nearly all living things possess enzymes known as peroxidases, which harmlessly and catalytically decompose low concentrations of hydrogen peroxide to water and oxygen, MnO−4 A permanganate is the general name for a chemical compound containing the manganate ion, (MnO4−). Because manganese is in the +7 oxidation state, the manganate(VII) ion is a strong oxidizing agent. The ion has tetrahedral geometry. Permanganate solutions are purple in color and are stable in neutral or slightly alkaline media, CrO3 Chromium trioxide is the inorganic compound with the formula CrO3. It is the acid anhydride of chromic acid, and is sometimes marketed under the same name. This compound is a dark red/orange brown solid, which dissolves in water concomitant with hydrolysis. Millions of kilograms are produced annually, mainly for electroplating, Cr2O2−7 Chromates and dichromates are salts of chromic acid and dichromic acid, respectively. Chromate salts contain the chromate anion, Cr , OsO4 Osmium tetroxide is the chemical compound with the formula OsO4. The compound is noteworthy for its many uses, despite the rarity of osmium. It also has a number of interesting properties, one being that the solid is volatile) or highly electronegative Electronegativity, symbol χ , is a chemical property that describes the ability of an atom (or, more rarely, a functional group) to attract electrons (or electron density) towards itself. An atom's electronegativity is affected by both its atomic weight and the distance that its valence electrons reside from the charged nucleus. The higher the substances/elements that can gain one or two extra electrons by oxidizing a element or substance (O Oxygen (pronounced /ˈɒksɨdʒɨn/, OK-si-jin, from the Greek roots ὀξύς (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter), is the element with atomic number 8 and represented by the symbol O. It is a member of the chalcogen group on the periodic table, and is a highly, F Fluorine is the chemical element with atomic number 9, represented by the symbol F. Fluorine forms a single bond with itself in elemental form, resulting in the diatomic F2 molecule. F2 (fluorine) is a supremely reactive, poisonous, pale, yellowish brown gas. Elemental fluorine is the most chemically reactive and electronegative of all the, Cl Chlorine (pronounced /ˈklɔriːn/ KLOR-een, from the Greek word 'χλωρóς' (khlôros, meaning 'pale green'), is the chemical element with atomic number 17 and symbol Cl. It is a halogen, found in the periodic table in group 17 (formerly VII, VIIa, or VIIb). As the chloride ion, which is part of common salt and other compounds, it is abundant, Br Bromine (pronounced /ˈbroʊmiːn/ BROH-meen or /ˈbroʊmɨn/ BROH-min; from Greek: βρῶμος, brómos, meaning "stench "), is a chemical element with the symbol Br and atomic number 35. It is in the halogen element group. Bromine vapors are corrosive and toxic. Approximately 556,000 metric tons were produced in 2007. The main).
Reducers
Substances that have the ability to reduce other substances are said to be reductive and are known as reducing agents A reducing agent is the element or compound in a redox (reduction-oxidation) reaction (see electrochemistry) that reduces another species. In doing so, it becomes oxidized, and is therefore the electron donor in the redox. For example consider the following reaction:, reductants, or reducers. That is, the reductant transfers electrons to another substance, and is thus itself oxidized. And, because it "donates" electrons, it is also called an electron donor An electron donor is a chemical entity that donates electrons to another compound. It is a reducing agent that, by virtue of its donating electrons, is itself oxidized in the process. Electron donors can also form charge transfer complexes A charge-transfer complex or electron-donor-acceptor complex is a chemical association of two or more molecules, or of different parts of one very large molecule, in which the attraction between the molecules (or parts) is created by an electronic transition into an excited electronic state, such that a fraction of electronic charge is transferred with electron acceptors.
Reductants in chemistry are very diverse. Electropositive Electropositivity is a measure of an element's ability to donate electrons, and therefore form positive ions. Mainly, this is an attribute of metals, meaning that for the most part, the greater the metallic character of an element, the greater the electropositivity. Therefore the alkali metals are most electropositive of all. This is because they elemental metals A metal is a chemical element that is a good conductor of both electricity and heat and forms cations and ionic bonds with non-metals. In chemistry, a metal is an element, compound, or alloy characterized by high electrical conductivity. In a metal, atoms readily lose electrons to form positive ions (cations). Those ions are surrounded by, such as lithium Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly reactive and flammable. For this reason, lithium metal, sodium Sodium is a metallic element with a symbol Na (from Latin natrium or Arabic ناترون natrun; perhaps ultimately from Egyptian netjerj) and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals within "group 1" (formerly known as ‘group IA’). It has only one stable isotope, 23Na, magnesium Magnesium is a chemical element with the symbol Mg, atomic number 12 and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust, where it constitutes about 2% by mass, and ninth in the known Universe as a whole. This preponderance of magnesium is related to the fact that it is easily, iron Iron is the most common element in the earth as a whole, and the fourth most common in the Earth's crust. It is produced as a result of stellar fusion in high-mass stars, and it is the heaviest stable element produced by stellar fusion because the fusion of iron is the last nuclear fusion reaction that is exothermic. Iron is the most widely used, zinc, aluminium Aluminium (UK: /ˌæljʉˈmɪniəm/ AL-yew-MIN-ee-əm) or aluminum (US: /əˈluːmɨnəm/ ( listen) ə-LOO-mi-nəm) is a silvery white member of the boron group of chemical elements. It has the symbol Al and its atomic number is 13. It is not soluble in water under normal circumstances. Aluminium is the most abundant metal in the Earth's crust,, carbon Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. There are three naturally occurring isotopes, with 12C and 13C being stable, while 14C is radioactive, decaying with a half-life of, are good reducing agents. These metals donate or give away electrons readily. Hydride transfer reagents, such as NaBH4 and LiAlH4, are widely used in organic chemistry Organic chemistry is a discipline within chemistry that involves the scientific study of the structure, properties, composition, reactions, and preparation of carbon-based compounds, hydrocarbons, and their derivatives. These compounds may contain any number of other elements, including hydrogen, nitrogen, oxygen, the halogens as well as,[1][2] primarily in the reduction of carbonyl In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O compounds to alcohols In chemistry, an alcohol is any organic compound in which a hydroxyl functional group (-O . Another method of reduction involves the use of hydrogen gas (H2) with a palladium Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46. Palladium is a rare and lustrous silvery-white metal that was discovered in 1803 by William Hyde Wollaston, who named it after the asteroid Pallas, which was named after the epithet of the Greek goddess Athena, acquired by her when she slew Pallas, platinum Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is in Group 10 of the periodic table of elements. A dense, malleable, ductile, precious, gray-white transition metal,, or nickel Nickel is a chemical element, with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. It is one of the four ferromagnetic elements that exist around room temperature, the other three being iron, cobalt and gadolinium catalyst Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations. Catalysts that speed the reaction are called positive. These catalytic reductions are used primarily in the reduction of carbon-carbon double or triple bonds.
Examples of redox reactions
A good example is the reaction between hydrogen and fluorine in which hydrogen is being oxidized and fluorine is being reduced:
- H2 + F2 → 2 HF
We can write this overall reaction as two half-reactions:
the oxidation reaction:
- H2 → 2 H+ + 2 e−
and the reduction reaction:
- F2 + 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 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 → 2 H+ + 2 e− F2 + 2 e− → 2 F− H2 + F2 → 2 H+ + 2 F−
And the ions combine to form hydrogen fluoride:
- H2 + F2 → 2 H+ + 2 F− → 2 HF
Displacement reactions
Redox occurs in single displacement reactions or substitution reactions. The redox component of these types of reactions is the change of oxidation state (charge) on certain atoms, not the actual exchange of atoms in the compounds.
For example, in the reaction between iron and copper(II) sulfate solution:
- Fe + CuSO4 → FeSO4 + Cu
The ionic equation for this reaction is:
- Fe + Cu2+ → Fe2+ + Cu
As two half-equations, it is seen that the iron is oxidized:
- Fe → Fe2+ + 2 e−
And the copper is reduced:
- Cu2+ + 2 e− → Cu
Other examples
- The oxidation of iron(II) to iron(III) by hydrogen peroxide in the presence of an acid:
-
- Fe2+ → Fe3+ + e−
- H2O2 + 2 e− → 2 OH−
- Overall equation:
-
- 2 Fe2+ + H2O2 + 2 H+ → 2 Fe3+ + 2 H2O
- The reduction of nitrate to nitrogen in the presence of an acid (denitrification):
-
- 2 NO3− + 10 e− + 12 H+ → N2 + 6 H2O
- Oxidation of elemental iron to iron(III) oxide by oxygen (commonly known as rusting, which is similar to tarnishing):
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- 4 Fe + 3 O2 → 2 Fe2O3
- The combustion of hydrocarbons, such as in an internal combustion engine, which 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, the stepwise oxidation of a hydrocarbon by oxygen produces water and, successively, an alcohol, an aldehyde or a ketone, a carboxylic acid, and then a peroxide.
Redox reactions in industry
The primary process of reducing ore to produce metals is discussed in the article on Smelting.
Oxidation is used in a wide variety of industries such as in the production of cleaning products and oxidising ammonia to produce nitric acid, which is used in most fertilizers.
Redox reactions are the foundation of electrochemical cells.
The production of compact discs depends on a redox reaction, which coats the disc with a thin layer of metal film.
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Oxidation reduction potential is one of the key benefits to ionized alkaline water.. uk.video.yahoo.com.
