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Carbon Monoxide

Carbon monoxide

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. Carbon monoxide has many common sources. The exhaust of an internal combustion engine, when burning a carbon-based fuel (i.e. almost any fuel except pure hydrogen) contains carbon monoxide, especially when the temperature is too low to effect complete oxidation of the hydrocarbons in the fuel to water and carbon dioxide, because the time (i.e., the residence time) available in the combustion chamber is too short, or because there is insufficient oxygen present. Usually, it is more difficult to design and operate a combustor for very low CO than for very low unburned hydrocarbons. Carbon monoxide is also present in small but significant concentrations in cigarette smoke. In the home, CO gas forms when fuels like natural gas, oil or wood do not burn completely in appliances such as furnaces and stoves, water heaters, ranges and ovens. Thus, common sources of carbon monoxide include leaky heat exchangers in furnaces; improperly or blocked vents for gas appliances, fireplaces and stoves; idling vehicles in attached or underground garages; or large collections of idling vehicles. Carbon monoxide gases can percolate through concrete hours after vehicles have left a garage. In the past a significant source of CO was Town gas, used for illumination and heating from the 19th century. Town gas was made by passing steam through red-hot coke; the resultant reaction between the water and carbon generated a mixture of hydrogen and carbon monoxide. Town gas has now been replaced by natural gas (methane). Wood gas, the result of the incomplete combustion of wood, also contains carbon monoxide as a major component.

Toxicity

Carbon monoxide is very dangerous, as inhaling excessively high amounts of it will lead to hypoxic injury, neurological damage, and possibly death. A concentration of as little as 0.1% carbon monoxide in the air can be fatal

History

Carbon monoxide was first prepared by the French chemist de Lassone in 1776 by heating zinc oxide with coke but thought it to be hydrogen by mistake as it burned with a blue flame. It was identified as a compound containing carbon and oxygen by the English chemist William Cruikshank in the year 1800. The toxic properties of CO were first thoroughly investigated by the French physiologist Claude Bernard around 1846. He poisoned dogs with the gas, and noticed that their blood was more rutilant in all the vessels. 'Rutilant' is a French word, but also has an entry in English dictionaries, meaning ruddy, shimmering, or golden. However, it was translated at the time as crimson, scarlet, and now is famously known as 'cherry pink'.

Chemistry

The structure of the CO molecule is best described using molecular orbital theory. The length of the bond (0.111 nm) indicates that it has a partial triple bond character. The molecule has a small dipole moment and is often represented by three resonance structures: 400px Note that the octet rule is violated for the carbon atom in the two structures on the right. The metal nickel forms a volatile compound with carbon monoxide, known as nickel carbonyl. The carbonyl decomposes readily back to the metal and gas, and this was used as the basis for the industrial purification of nickel. Many other metals may form carbonyl complexes containing covalently attached carbon monoxide, these can be made by a range of different methods for instance boiling ruthenium trichloride with triphenyl phosphine in methoxyethanol (or DMF) the complex [RuHCl(CO)(PPh₃)₃] can be obtained. Nickel carbonyl is special as it can be formed by the direct combination of carbon monoxide and nickel metal at room temperature. As in nickel carbonyl and other carbonyls, the electron pair on the carbon bonded to the metal. In this case carbon monoxide is regarded as a carbonyl ligand. Carbon monoxide and methanol are reacted together using a homogenous rhodium catalyst to form acetic acid in the Monsanto process, which is responsible for most of the industrial production of acetic acid. The CAS registry number of carbon monoxide is 630-08-0.

Carbon monoxide in the atmosphere

CAS registry number global carbon monoxide ]] Carbon monoxide has an indirect radiative forcing effect by elevating concentrations of methane and tropospheric ozone through chemical reactions with other atmospheric constituents (e.g., the hydroxyl radical, OH) that would otherwise destroy them. Carbon monoxide is created when carbon-containing fuels are burned incompletely. Through natural processes in the atmosphere, it is eventually oxidized to carbon dioxide. Carbon monoxide concentrations are both short-lived in the atmosphere and spatially variable.

External links

- [http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc00/icsc0023.htm International Chemical Safety Card 0023]
- [http://www.cdc.gov/niosh/npg/npgd0105.html NIOSH Pocket Guide to Chemical Hazards]
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- National Pollutant Inventory http://www.npi.gov.au Australia's Pollutant Emissions Database Category:Oxides Category:Inorganic carbon compounds Category:Pollutants Category:Smog Category:Toxicology ko:일산화 탄소 ja:一酸化炭素

Gas

:For other meanings see gas (disambiguation). ---- A gas is one of the four main phases of matter (after solid and liquid, and followed by plasma), that subsequently appear as a solid material is subjected to increasingly higher temperatures. Thus, as energy in the form of heat is added, a solid (e.g. ice) will first melt to become a liquid (e.g. water), which will then boil or evaporate to become a gas (e.g. water vapor). In some circumstances, a solid (e.g. "dry ice") can directly turn into a gas: this is called sublimation. If the gas is further heated, its atoms or molecules can become (wholly or partially) ionized, turning the gas into a plasma.

Properties of a gas

#All collisions are perfectly elastic #The gas fills the entire container #The molecules have negligible volume In the gas phase, the atoms or molecules constituting the matter basically move independently, with no forces keeping them together or pushing them apart. Their only interactions are rare and random collisions. The particles move in random directions, at high speeds, whose range is dependent on the temperature and defined by the Maxwell-Boltzmann distribution. Therefore, the gas phase is a completely disordered state. Following the second law of thermodynamics, gas particles will immediately diffuse to homogeneously fill any shape or volume of space that is made available to them. The thermodynamic state of a gas is characterized by its volume, its temperature, which is determined by the average velocity or kinetic energy of the molecules, and its pressure, which is determined by the average velocity and density or number of molecules. These variables are related by the fundamental gas laws, which state that the pressure in an ideal gas is proportional to its temperature and number of molecules, but inversely proportional to its volume. Like liquids and plasmas, gases are fluids: they have the ability to flow and do not tend to return to their former configuration after deformation, although they do have viscosity. Unlike liquids, however, unconstrained gases do not occupy a fixed volume, but expand to fill whatever space they occupy. The kinetic energy per molecule in a gas is the second greatest of the states of matter (after plasma). Because of this high kinetic energy, gas atoms and molecules tend to bounce off of any containing surface and off one another, the more powerfully as the kinetic energy is increased. A common misconception is that the collisions of the molecules with each other is essential to explain gas pressure, but in fact their random velocities are sufficient to define that quantity. Mutual collisions are important only for establishing the Maxwell-Boltzmann distribution. Gas particles are normally well separated, as opposed to liquid particles, which are in contact. A material particle (say a dust mote) in a gas moves in Brownian Motion. Since it is at the limit of (or beyond) current technology to observe individual gas particles (atoms or molecules), only theoretical calculations give suggestions as to how they move, but their motion is different from Brownian Motion. The reason is that Brownian Motion involves a smooth drag due to the frictional force of many gas molecules, punctuated by violent collisions of an individual (or several) gas molecule(s) with the particle. The particle (generally consisting of millions or billions of atoms) thus moves in a jagged course, yet not so jagged as we would expect to find if we could examine an individual gas molecule.

Etymology

The word "gas" was apparently coined in the early 17th century by the Belgian chemist Jan Baptist van Helmont, as a re-spelling of his pronunciation of the Greek word chaos.

Carbon

:Alternative meaning: Carbon (API) :For the portable music player, see Rio Carbon Carbon is a chemical element in the periodic table that has the symbol C and atomic number 6. An abundant nonmetallic, tetravalent element, carbon has several allotropic forms:
- Diamond (hardest known natural mineral). Structure: each atom is bonded tetrahedrally to four others, making a 3-dimensional network of puckered six-membered rings of atoms.
- Graphite (one of the softest substances). Structure: each atom is bonded trigonally to three other atoms, making a 2-dimensional network of flat six-membered rings; the flat sheets are loosely bonded.
- Fullerenes. Structure: comparatively large molecules formed completely of carbon bonded trigonally, forming spheroids (of which the best-known and simplest is the buckminsterfullerene or buckyball).
- Chaoite A mineral supposedly formed in meteorite impacts.
- Lonsdaleite (a corruption of diamond). Structure: similar to diamond, but forming a hexagonal crystal lattice.
- Amorphous carbon (a glassy substance). Structure: an assortment of carbon molecules in a non-crystalline, irregular, glassy state.
- Carbon nanofoam (an extremely light magnetic web). Structure: a low-density web of graphite-like clusters, in which the atoms are bonded trigonally in six- and seven-membered rings.
- Carbon nanotubes (tiny tubes). Structure: each atom is bonded trigonally in a curved sheet that forms a hollow cylinder.
- Aggregated diamond nanorods, the most recently discovered allotrope. Lamp black consists of small graphitic areas. These areas are randomly distributed, so the whole structure is isotropic. 'Glassy carbon' is isotropic and contains a high proportion of closed porosity. Unlike normal graphite, the graphitic layers are not stacked like pages in a book, but have a more random arrangement. Carbon fibers are similar to glassy carbon. Under special treatment (stretching of organic fibers and carbonization) it is possible to arrange the carbon planes in direction of the fiber. Perpendicular to the fiber axis there is no orientation of the carbon planes. The result are fibers with a higher specific strength than steel. Carbon occurs in all organic life and is the basis of organic chemistry. This nonmetal also has the interesting chemical property of being able to bond with itself and a wide variety of other elements, forming nearly 10 million known compounds. When united with oxygen it forms carbon dioxide which is absolutely vital to plant growth. When united with hydrogen, it forms various compounds called hydrocarbons which are essential to industry in the form of fossil fuels. When combined with both oxygen and hydrogen it can form many groups of compounds including fatty acids, which are essential to life, and esters, which give flavor to many fruits. The isotope carbon-14 is commonly used in radioactive dating.

Notable characteristics

Carbon is a remarkable element for many reasons. Its different forms include one of the softest (graphite) and one of the hardest (diamond) substances known to humankind. Moreover, it has a great affinity for bonding with other small atoms, including other carbon atoms, and its small size makes it capable of forming multiple bonds. Because of these properties, carbon is known to form nearly ten million different compounds, the large majority of all chemical compounds. Carbon compounds form the basis of all life on Earth and the carbon-nitrogen cycle provides some of the energy produced by the sun and other stars. Moreover, carbon has the highest melting/sublimation point of all elements. At atmospheric pressure it has no actual melting point as its triple point is at 10 MPa (100 bar) so it sublimates above 4000 K. Thus it remains solid at higher temperatures than the highest melting point metals like tungsten or rhenium, regardless of its allotropic form. Carbon was not created in the Big Bang due to the fact that it needs a triple collision of alpha particles (helium nuclei) to be produced. The universe initially expanded and cooled too fast for that to be possible. It is produced, however, in the interior of stars in the horizontal branch, where stars transform a helium core into carbon by means of the triple-alpha process. It was also created in a multi atomic state.

Applications

Carbon is a vital component of all known living systems, and without it life as we know it could not exist (see alternative biochemistry). The major economic use of carbon is in the form of hydrocarbons, most notably the fossil fuels methane gas and crude oil (petroleum). Crude oil is used by the petrochemical industry to produce, amongst others, gasoline and kerosene, through a distillation process, in refineries. Crude oil forms the raw material for many synthetic substances, many of which are collectively called plastics.

Other uses

- The isotope Carbon-14 was discovered in February 27 1940 and is used in radiocarbon dating.
- Some smoke detectors use tiny amounts of a radioactive isotope of carbon as source of ionizing radiation. (Most smoke detectors of this type use an isotope of americium.)
- Graphite is combined with clays to form the 'lead' used in pencils.
- Diamond is used for decorative purposes, and also as drill bits and other applications making use of its hardness.
- Carbon is added to iron to make steel.
- Carbon is used as a neutron moderator in nuclear reactors.
- Graphite carbon in a powdered, caked form is used as charcoal for cooking, artwork and other uses.
- Activated charcoal is used in medicine (as powder or compounded in tablets or capsules) to absorb toxins or poisons from the digestive system. The chemical and structural properties of fullerenes, in the form of carbon nanotubes, has promising potential uses in the nascent field of nanotechnology. Nanoparticles might however be toxic.

History and Etymology

Carbon was discovered in prehistory and was known to the ancients, who manufactured it by burning organic material in insufficient oxygen (making charcoal). Diamonds have long been considered rare and beautiful. One of the last-known allotropes of carbon, fullerenes, were discovered as byproducts of molecular beam experiments in the 1980s. The name comes from French charbone, which in turn came from Latin carbo, meaning charcoal. In German and Dutch, the names for carbon are Kohlenstoff and koolstof respectively, both literally meaning "coal-stuff".

Allotropes

The allotropes of carbon are the different molecular configurations (allotropes) that pure carbon can take. The three relatively well-known allotropes of carbon are amorphous carbon, graphite, and diamond. Several exotic allotropes have also been synthesized or discovered, including fullerenes, carbon nanotubes, lonsdaleite and aggregated diamond nanorods. In its amorphous form, carbon is essentially graphite but not held in a crystalline macrostructure. It is, rather, present as a powder which is the main constituent of substances such as charcoal, lamp black (soot) and activated carbon. activated carbon, so that two phases can coexist. ]] At normal pressures carbon takes the form of graphite, in which each atom is bonded to three others in a plane composed of fused hexagonal rings, just like those in aromatic hydrocarbons. The two known forms of graphite, alpha (hexagonal) and beta (rhombohedral), both have identical physical properties, except for their crystal structure. Graphites that naturally occur have been found to contain up to 30% of the beta form, when synthetically-produced graphite only contains the alpha form. The alpha form can be converted to the beta form through mechanical treatment and the beta form reverts back to the alpha form when it is heated above 1000 °C. Because of the delocalization of the pi-cloud, graphite conducts electricity. The material is soft and the sheets, frequently separated by other atoms, are held together only by van der Waals forces, so easily slip past one another. At very high pressures carbon forms an allotrope called diamond, in which each atom is bonded to four others. Diamond has the same cubic structure as silicon and germanium and, thanks to the strength of the carbon-carbon bonds, is together with the isoelectronic boron nitride (BN) the hardest substance in terms of resistance to scratching. The transition to graphite at room temperature is so slow as to be unnoticeable. Under some conditions, carbon crystallizes as Lonsdaleite, a form similar to diamond but hexagonal. Fullerenes have a graphite-like structure, but instead of purely hexagonal packing, also contain pentagons (or possibly heptagons) of carbon atoms, which bend the sheet into spheres, ellipses or cylinders. The properties of fullerenes (also called "buckyballs" and "buckytubes") have not yet been fully analyzed. All the names of fullerenes are after Buckminster Fuller, developer of the geodesic dome, which mimics the structure of "buckyballs". A nanofoam allotrope has been discovered which is ferromagnetic. Carbon allotropes include:
- Amorphous carbon
- Carbon nanofoam (discovered in 1997)
- Carbon nanotube
- Diamond
- Fullerene
- Graphite
- Lonsdaleite
- Aggregated diamond nanorods (synthesised in 2005) The system of carbon allotropes spans a range of extremes. Between diamond and graphite:
- Graphite is soft and is used in pencils
- Diamond is the hardest mineral known to man (although aggregated diamond nanorods are now believed to be even harder), but graphite is one of the softest.
- Diamond is the ultimate abrasive, but graphite is a very good lubricant.
- Diamond is an excellent electrical insulator, but graphite is a conductor of electricity.
- Diamond is usually transparent, but graphite is opaque.
- Diamond crystallizes in the cubic system but graphite crystallizes in the hexagonal system. Between amorphous carbon and nanotubes:
- Amorphous carbon is among the easiest materials to synthesize, but carbon nanotubes are extremely expensive to make.
- Amorphous carbon is completely isotropic, but carbon nanotubes are among the most anisotropic materials ever produced.

Occurrence

There are nearly ten million carbon compounds known to science. Many thousands of these are vital to life processes. They are also many organic-based reactions of economic importance. Carbon is abundant in the sun, stars, comets, and in the atmospheres of most planets. Some meteorites contain microscopic diamonds that were formed when the solar system was still a protoplanetary disk. In combination with other elements, carbon is found the earth's atmosphere and dissolved in all water bodies. With smaller amounts of calcium, magnesium, and iron, it is a major component of very large masses carbonate rock (limestone, dolomite, marble etc.). When combined with hydrogen, carbon forms coal, petroleum, and natural gas which are called hydrocarbons. Graphite is found in large quantities in New York and Texas, the United States; Russia; Mexico; Greenland and India. Natural diamonds occur in the mineral kimberlite found in ancient volcanic "necks," or "pipes". Most diamond deposits are in Africa, notably in South Africa, Namibia, Botswana, the Republic of the Congo and Sierra Leone. There are also deposits in Arkansas, Canada, the Russian Arctic, Brazil and in Northern and Western Australia.

Organic compounds

The most prominent oxide of carbon is carbon dioxide, CO₂. This is a minor component of the Earth's atmosphere, produced and used by living things, and a common volatile elsewhere. In water it forms trace amounts of methanoic acid, HCO₂H, but as most compounds with multiple single-bonded oxygens on a single carbon it is unstable. Through this intermediate, though, resonance-stabilized carbonate ions are produced. Some important minerals are carbonates, notably calcite. Carbon disulfide, CS₂, is similar. The other oxides are carbon monoxide, CO, and the uncommon carbon suboxide, C₃O₂. Carbon monoxide is formed by incomplete combustion, and is a colorless, odorless gas. The molecules each contain a triple bond and are fairly polar, resulting in a tendency to bind permanently to haemoglobin molecules, so that the gas is highly poisonous. Cyanide, CN-, has a similar structure and behaves a lot like a halide ion; the nitride cyanogen, (CN)₂, is related. With reactive metals, such as tungsten, carbon forms either carbides, C^-, or acetylides, C₂^2- to form alloys with very high melting points. These anions are also associated with methane and acetylene, both very weak acids. All in all, with an electronegativity of 2.5, carbon prefers to form covalent bonds. A few carbides are covalent lattices, like carborundum, SiC, which resembles diamond.

Carbon chains

Carbon has the ability to form long chains with interconnecting C-C bonds. This property is called Catenation. Carbon-Carbon bonds are fairly strong, and abnormaly stable. This property is important as it allows carbon to form a huge number of compounds; if fact, there are more known carbon-containing compounds than all the other compounds of the chemical elements combined! The simplest form of an organic molecule is the hydrocarbon - a large family of organic molecules that, by definition, are composed of hydrogen atoms bonded to a chain of carbon atoms. Chain length, side chains and functional groups all affect the properties of organic molecules.

Carbon cycle

Under terrestrial conditions, conversion of one isotope to another is very rare. Therefore, for practical purposes, the amount of carbon on Earth is constant. Thus processes that use carbon must obtain it from somewhere, and dispose of it somewhere. The paths that carbon follows in the environment are called the carbon cycle. For example, plants draw carbon dioxide out of the environments and use it to build biomass. Some of this biomass is eaten by animals, where some of it is exhaled as carbon dioxide. The carbon cycle is considerably more complicated than this short loop; for example, some carbon dioxide is dissolved in the oceans; dead plant or animal matter may become sedimentary rock, and so forth.

Isotopes

Carbon has two stable, naturally-occurring isotopes: carbon-12, or ¹²C, (98.89%) and carbon-13, or ¹³C, (1.11%), and one unstable, naturally-occurring, radioisotope; carbon-14 or ¹⁴C. There are 15 known isotopes of carbon and the shortest-lived of these is ⁸C which decays through proton emission and alpha decay. It has a half-life of 1.98739x10^-21 s. In 1961 the International Union of Pure and Applied Chemistry adopted the isotope carbon-12 as the basis for atomic weights. Carbon-14 has a half-life of 5730 y and has been used extensively for radiocarbon dating carbonaceous materials.

Precautions

Carbon is relatively safe. Inhalation of fine soot in large quantities can be dangerous. Carbon may catch fire at very high temperatures and burn vigorously (as in the Windscale fire). There are a tremendous number of carbon compounds; some are lethally poisonous (cyanide, CN^-), and some are essential to life (dextrose).

References

- [http://lbruno.home.cern.ch/lbruno/documents/Bibliography/LHC_Note_78.pdf On Graphite Transformations at High Temperature and Pressure Induced by Absorption of the LHC Beam], J.M. Zazula, 1997
- WebElements.com and EnvironmentalChemistry.com per the guidelines at [http://en.wikipedia.org/wiki/Wikipedia:WikiProject_Elements Wikipedia's WikiProject Elements]

External links

- [http://periodic.lanl.gov/elements/6.html Los Alamos National Laboratory – Carbon]
- [http://www.webelements.com/webelements/elements/text/C/index.html WebElements.com – Carbon]
- [http://education.jlab.org/itselemental/ele006.html It's Elemental – Carbon]
- [http://www.vincentherr.com/cf/ – Carbon Fullerene and other Allotropes] models by Vincent Herr
- [http://invsee.asu.edu/nmodules/Carbonmod/everywhere.html Extensive Carbon page at asu.edu]
- [http://electrochem.cwru.edu/ed/encycl/art-c01-carbon.htm Electrochemical uses of carbon]
- [http://www.compchemwiki.org/index.php?title=Carbon Computational Chemistry Wiki] Category:Chemical elements Category:Nonmetals Category:Materials ko:탄소 ms:Karbon ja:炭素 simple:Carbon th:คาร์บอน

Oxygen

Oxygen is a chemical element in the periodic table. It has the symbol O and atomic number 8. The element is very common, found not only on Earth but throughout the universe, usually covalently bonded with other elements. Unbound oxygen (usually called molecular oxygen, O₂, a diatomic molecule) first appeared on Earth during the Paleoproterozoic era (between 2500 million years ago and 1600 million years ago) and as a product of the metabolic action of early anaerobes (archaea and bacteria). The presence of free oxygen drove most of the organisms then living to extinction. The atmospheric abundance of free oxygen in later geological epochs and up to the present has been largely driven by photosynthetic organisms, roughly three quarters by phytoplankton and algae in the oceans and one quarter from terrestrial plants.

Characteristics

At standard temperature and pressure, oxygen is mostly found as a gas consisting of a diatomic molecule with the chemical formula O₂. O₂ has two energetic forms:
- The low-energy predominant single-bonded diradical triplet oxygen. This native diradical quality of oxygen contributes to its destructive chemical nature. This form is stabilized by the degeneracy effect.
- The high-energy double-bonded molecule singlet oxygen. Oxygen is a major component of air, produced by plants during photosynthesis, and is necessary for aerobic respiration in animals. The word oxygen derives from two words in Greek, οξυς (oxys) (acid, sharp) and γεινομαι (geinomai) (engender). The name "oxygen" was chosen because, at the time it was discovered in the late 18th century, it was believed that all acids contained oxygen. The definition of acid has since been revised to not require oxygen in the molecular structure. Liquid O₂ and solid O₂ have a light blue color and both are highly paramagnetic. Liquid O₂ is usually obtained by the fractional distillation of liquid air. Liquid and solid O₃ (ozone) have a deeper color of blue. A recently discovered allotrope of oxygen, tetraoxygen (O₄), is a deep red solid that is created by pressurizing O₂ to the order of 20 GPa. Its properties are being studied for use in rocket fuels and similar applications, as it is a much more powerful oxidizer than either O₂ or O₃.

Applications

Liquid oxygen finds use as an oxidizer in rocket propulsion. Oxygen is essential to respiration, so oxygen supplementation has found use in medicine (as oxygen therapy). People who climb mountains or fly in airplanes sometimes have supplemental oxygen supplies (as air). Oxygen is used in welding (such as the oxyacetylene torch), and in the making of steel and methanol. Oxygen presents two absorption bands centered in the wavelengths 687 and 760 nanometers. Some scientists have proposed to use the measurement of the radiance coming from vegetation canopies in those oxygen bands to characterize plant health status from a satellite platform. This is because in those bands, it is possible to discriminate the vegetation's reflectance from the vegetation's fluorescence, which is much weaker. The measurement presents several technical difficulties due to the low signal to noise ratio and due to the vegetation's architecture, but it has been proposed as possibility to monitor the carbon cycle from satellite, thus in a global scale. Oxygen, as a mild euphoric, has a history of recreational use that extends into modern times. Oxygen bars can be seen at parties to this day. In the 19th century, oxygen was often mixed with nitrous oxide to promote an analgesic effect; indeed, such a mixture (Entonox) is commonly used in medicine today.

History

Oxygen was first discovered by Michał Sędziwój, Polish alchemist and philosopher in late 16th century. Sędziwój assumed the existence of oxygen by warming nitre (saltpeter). He thought of the gas given off as "the elixir of life". Oxygen was again discovered by the Swedish pharmacist Carl Wilhelm Scheele sometime before 1773, but the discovery was not published until after the independent discovery by Joseph Priestley on August 1, 1774, who called the gas dephlogisticated air (see phlogiston theory). Priestley published his discoveries in 1775 and Scheele in 1777; consequently Priestley is usually given the credit. It was named by Antoine Laurent Lavoisier after Priestley's publication in 1775.

Occurrence

Oxygen is the second most common component of the earth's atmosphere (20.947% by volume).

Compounds

Due to its electronegativity, oxygen forms chemical bonds with almost all other elements (which is the origin of the original definition of oxidation). The only elements to escape the possibility of oxidation are a few of the noble gases. The most famous of these oxides is dihydrogen monoxide, or water (H₂O). Other well known examples include compounds of carbon and oxygen, such as carbon dioxide (CO₂), alcohols (R-OH), aldehydes, (R-CHO), and carboxylic acids (R-COOH). Oxygenated radicals such as chlorates (ClO₃⁻), perchlorates (ClO₄⁻), chromates (CrO₄²⁻), dichromates (Cr₂O₇²⁻), permanganates (MnO₄⁻), and nitrates (NO₃⁻) are strong oxidizing agents in and of themselves. Many metals such as iron bond with oxygen atoms, iron (III) oxide (Fe₂O₃). Ozone (O₃) is formed by electrostatic discharge in the presence of molecular oxygen. A double oxygen molecule (O₂)₂ is known and is found as a minor component of liquid oxygen. Epoxides are ethers in which the oxygen atom is part of a ring of three atoms.

Isotopes

Oxygen has fifteen known isotopes with atomic masses ranging from 12 to 26. Three of them are stable and twelve are radioactive. The radioisotopes all have half lives of less than three minutes. The stable isotopes have mass numbers of 16, 17 and 18, of which oxygen-16 is the most common (over 99%).

Precautions

Oxygen can be toxic at elevated partial pressures (i.e. high relative concentrations). This is important in some forms of scuba diving, such as with a rebreather. Certain derivatives of oxygen, such as ozone (O₃), singlet oxygen, hydrogen peroxide, hydroxyl radicals and superoxide, are also highly toxic. The body has developed mechanisms to protect against these toxic species. For instance, the naturally-occurring glutathione can act as an antioxidant, as can bilirubin which is normally a breakdown product of hemoglobin. Highly concentrated sources of oxygen promote rapid combustion and therefore are fire and explosion hazards in the presence of fuels. This is true as well of compounds of oxygen such as chlorates, perchlorates, dichromates, etc. Compounds with a high oxidative potential can often cause chemical burns. The fire that killed the Apollo 1 crew on a test launchpad spread so rapidly because the pure oxygen atmosphere was at normal atmospheric pressure instead of the one third pressure that would be used during an actual launch. (See partial pressure.) Oxygen derivatives are prone to form free radicals, especially in metabolic processes. Because they can cause severe damage to cells and their DNA, they are thought to be related to cancer and aging.

References

- [http://periodic.lanl.gov/elements/8.html Los Alamos National Laboratory – Oxygen]
- [http://physics.nist.gov/cgi-bin/AtData/main_asd Nist atomic spectra database]
- [http://chartofthenuclides.com/default.html Nuclides and Isotopes Fourteenth Edition]: Chart of the Nuclides, General Electric Company, 1989

External links

- [http://www.priestleysociety.net Priestley Society, Dedicated to Joseph Priestley the man who discovered oxygen]
- [http://www.best-home-remedies.com/minerals/oxygen.htm Oxygen - Benefits, Deficiency Symptoms And Food Sources]
- [http://www.josephpriestley.info Joseph Priestley Information Website, about the man who discovered oxygen]
- [http://periodic.lanl.gov/elements/8.html Los Alamos National Laboratory – Oxygen]
- [http://www.webelements.com/webelements/elements/text/O/index.html WebElements.com – Oxygen]
- [http://education.jlab.org/itselemental/ele008.html It's Elemental – Oxygen]
- [http://members.tripod.com/tjaartdb0/html/oxygen_toxicity.html Oxygen Toxicity]
- [http://www.uigi.com/oxygen.html Oxygen (O2) Properties, Uses, Applications]
- [http://www.compchemwiki.org/index.php?title=Oxygen Computational Chemistry Wiki]
- [http://koti.mbnet.fi/antitz/dime/en Tests with liquid oxygen :-)] Category:Nonmetals Category:Chalcogens als:Sauerstoff ko:산소 ms:Oksigen ja:酸素 simple:Oxygen th:ออกซิเจน

Unburned hydrocarbon

Unburned hydrocarbons (UHCs) are the hydrocarbons emitted after petroleum is burned in an engine. Any fuel entering a flame will be reacted. Thus, when unburned fuel is emitted from a combustor, the emission is caused by fuel "avoiding" the flame zones. For example, in piston engines, some of the fuel-air mixture "hides" from the flame in the crevices provided by the [http://www.wellfar.com/index.html piston ring] grooves. Further, some regions of the combustion chamber may have a very weak flame, that is, they have either very fuel-lean or very fuel-rich conditions and consequently they have a low combustion temperature. These regions will cause intermediate species such as formaldehyde and alkenes to be emitted. Sometimes the term "products of incomplete combustion," or PICs, is used to describe such species. Bold textItalic text

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Town gas

Town gas is a generic term referring to manufactured gas produced for sale to consumers and municipalities. Depending on the processes used for its creation the gas was a mixture of caloric gases: hydrogen, carbon monoxide, methane, and volatile hydrocarbons with small amounts of noncaloric gases carbon dioxide and nitrogen as impurities. Prior to the development of natural gas supplies and transmission in the United States during 1940s and 1950s, virtually all fuel and lighting gas was manufactured, and the byproduct coal tars were at some times an important chemical feedstock for the chemical industries. The development of manufactured gas paralleled that of the industrial revolution and urbanization. The terms coal gas and manufactured gas are also common.

Manufacturing process

Manufactured gas is made by two processes: carbonization or gasification. Carbonization refers to the devolitalization of an organic feedstock to yield gas and char. Gasification is the process of subjecting a feedstock to chemical reactions that produce gas. The first process used was the carbonization and partial pyrolysis of coal. The off gases liberated in the high temperature carbonization (coking) of coal in coke ovens were collected, scrubbed and used as fuel. Depending on the goal of the plant, the desired product was either a high quality coke for metallurgical use, with the gas being a side product or the production of a high quality gas with coke being the side product. Coke plants are typically associated with metallurgical facilities such as smelters, and blast furnaces, while gas works typically served urban areas. A facility used to manufacture coal gas, Carbureted Water Gas (CWG), and oil gas is generally referred to today as a Manufactured Gas Plant (MGP). In the early years of MGP operations, the goal of a utility gas works was to produce the greatest amount of highly illuminating gas. The illuminating power of a gas was related to amount of soot forming hydrocarbons (“illuminants”) dissolved in it. These hydrocarbons gave the gas flame its characteristic bright yellow color. Gas works would typically use oily bituminous coals as feedstock. These coals would give off large amounts of volatile hydrocarbons into the coal gas, but would leave behind a crumbly, low quality coke not suitable for metallurgical processes. Coal or Coke oven gas typically had a caloric value (CV) between 1 and 2 MJ/m³ (250-550 Btu/ft³ (std)); with values around 2 MJ/m³ (550 Btu/ft³ (std)); being typical. The advent of electric lighting forced utilities to search for other markets for manufactured gas. MGPs that once produced gas almost exclusively for lighting shifted their efforts towards supplying gas primarliy for heating and cooking, and even refrigeration and cooling. Fuel gas for industrial use was made using producer gas technology. Producer gas is made by blowing air through an incandescent fuel bed (commonly coke or coal) in a gas producer. The reaction of fuel with insufficient air for total combustion produces CO: this reaction is exothermic and self sustaining. It was discovered that adding steam to the input air of a producer would increase the CV of the fuel gas by enriching it with CO and H₂ produced by water gas reactions. Producer gas has a very low CV of 3.7 to 5.6 MJ/m³ (100-150 Btu/ft³ (std)); because the calorific gases CO/H₂ are diluted with lots of inert nitrogen (from air) and CO₂ (from combustion)

2\ \mbox(s) + \mbox_2 \rightarrow 2\ \mbox

(Exothermic: Producer gas Reaction)

\mbox(s) + \mbox_2\mbox(g) \rightarrow \mbox + \mbox_2

(Endothermic: Water Gas Reaction)

\mbox+2\ \mbox_2\mbox\rightarrow \mbox_2+2\ \mbox_2

(Endothermic)

\mbox + \mbox_2\mbox \rightarrow \mbox_2 + \mbox_2

(Exothermic: Water Gas Shift reaction) The problem of nitrogen dilution was overcome by the blue water gas (BWG) process, developed in the 1850s by Sir William Siemens . The incandescent fuel bed would be alternately blasted with air followed by steam. The air reactions during the blow cycle are exothermic, heating up the bed, while the steam reactions during the make cycle, are endothermic and cool down the bed. The products from the air cycle contain non-caloric nitrogen and are exhausted out the stack while the products of the steam cycle are kept as blue water gas. This gas is composed almost entirely of CO and H₂, and burns with a pale blue flame similar to natural gas. BWG has a CV of 11 MJ/m³ (300 Btu/ft³ (std)). Because blue water gas lacked illuminants it would not burn with a luminous flame in a simple fishtail gas jet as existing prior to the discovery of the Welsbach mantle in the 1890s. Various attempts were made to enrich BWG with illuminants from gas oil in the 1860s. Gas oil was the flammable waste product from kerosene refining, made from the lightest and most volatile fractions (tops) of crude oil. In 1875 Thaddeus S. C. Lowe invented the carburetted water gas process. This process revolutionized the manufactured gas industry and was the standard technology until the end of manufactured gas era. A CWG generating set consisted of three elements; a producer (generator), carburettor and a super heater connected in series with gas pipes and valves. During a make run, steam would be passed through the generator to make blue water gas. From the generator the hot water gas would pass into the top of the carburetor where light petroleum oils would be injected into the gas stream. The light oils would be thermocracked as they came in contact with the white hot checkerwork firebricks inside the carburettor. The hot enriched gas would then flow into the superheater, where the gas would be further cracked by more hot fire bricks

Early history of gas production by carbonization

The Flemish scientist Jan Baptista van Helmont (1577 - 1644) discovered that a 'wild spirit' escaped from heated wood and coal, and, thinking that it 'differed little from the chaos of the ancients', he named it gas in his Origins of Medicine (c. 1609). Among several others who carried out similar experiments, were Johann Becker of Munich (c 1681) and about three years later John Clayton of Wigan England, the latter amusing his friends by lighting, what he called, "Spirit of the Coal". William Murdoch (later known as Murdock) (1754 - 1839) is reputed to have heated coal in his mother's teapot to produce gas. From this beginning, he discovered new ways of making, purifying and storing gas; illuminating his house at Redruth (or his cottage at Soho) in 1792, the entrance to the Manchester Police Commissioners premises in 1797, the exterior of the factory of Boulton and Watt in Birmingham, England, and a large cotton mill in Salford, Lancashire in 1805. Professor Jan Pieter Minckelers lit his lecture room at the University of Louvain in 1783 and Lord Dundonald lit his house at Culross, Scotland, in 1787, the gas being carried in sealed vessels from the local tar works. In France, Phillipe Lebon patented a gas fire in 1799 and demonstrated street lighting in 1801. Other demonstrations followed in France and in the United States, but, it is generally recognised that the first commercial gas works was built by the London and Westminster Gas Light and Coke Company in Great Peter Street in 1812 laying wooden pipes to illuminate Westminster Bridge with gas lights on New Year's Eve in 1813. In 1816, Rembrandt Peale and four others established the Gas Light Company of Baltimore, the first manufactured gas company in America. In 1821, natural gas was being used commercially in Fredonia, New York. The first German gas works was built in Hannover in 1825 and by 1870 there were 340 gas works in Germany making town gas from coal, wood, peat and other materials. Working conditions in the Gas Light and Coke Company's Horseferry Road Works, London, in the 1830s were described by a French visitor, Flora Tristan, in her Promenades Dans Londres
- - "Two rows of furnaces on each side were fired up; the effect was not unlike the description of Vulcan's forge, except that the Cyclops were animated with a divine spark, whereas the dusky servants of the English furnaces were joyless, silent and benumbed. ... The foreman told me that stokers were selected from among the strongest, but that nevertheless they all became consumptive after seven or eight years of toil and died of pulmonary consumption. That explained the sadness and apathy in the faces and every movement of the hapless men." The first public piped gas supply was to 13 gas lamps, each with three glass globes along the length of Pall Mall, London in 1807. The credit for this goes to the inventor and entrepreneur Fredrick Winsor and the plumber Thomas Sugg who made and laid the pipes. Digging up streets to lay pipes required legislation and this delayed the development of street lighting and gas dor domestic use. Meanwhile Wlliam Murdock and his pupil Samuel Clegg were installing gas lighting in factories and work places, encountering no such impediments.

Early history of gas production by gasification

1850s: Gas producers invented, water gas process discovered. Mond Gas: 1850s Europeans discover that using coal instead of coke in a producer results in producer gas that contains ammonia and coal tar, Ludwig Mond's Mond Gas is processed to recover these valuable compounds. 1860s: Enrichment of BWG with illuminants from gas oil circa 1860s. Gas Oils, the volatile fractions that evaporate above kerosene, are a major problem for kerosene industry. 1875: The invention of the Carburetted Water gas process by Prof. TSC Lowe in 1875. The gas oil is fixed into the BWG via thermocracking in the carburettor and superheater of the CWG generating set. CWG is the dominant technology from 1880s until 1950s, replacing coal gasification. CWG has a CV of 2 MJ/m³ i.e slightly more than half that of natural gas. Golden age of gas light develops with the Welsbach mantle.

The uses of gas and the later development of the gas industry

The advent of incandesant gas lighting in factories, homes and in the streets, replacing oil lamps and candles with steady clear light, almost matching daylight in its colour, turned night into day for many - making night shift work possible in industries where light was all important - in spinning, weaving and making up garments etc. There followed gas heaters, gas cookers, refrigerators, washing machines, hand irons, pokers for fire lighting, gas heated baths, remotely controlled clusters of gas lights, gas engines of various types and, in later years, gas central heating and air conditioning, all made immense contributions to the improvement of the quality of life in cities and towns world wide. By the 1960s, manufactured gas, compared with its main rival in the energy market, electricity, was considereed 'nasty, smelly, dirty and dangerous', to quote market research of the time, and seemed doomed to extinction. In Europe, salvation came with the discovery of commercial quantites of natural gas, mainly methane, in the province of Groningen in the Netherlands and the demonstration that liquid natural gas (LNG) could be transported efficiently and economically over long distances by sea. Later developments in the technologies of pipelaying have made possible the transmission of gas on land and under sea across and between continents. Natural gas is now a world commodity.

Historical References

- Barty-King, H. (1985) New Flame: How Gas changed the commercial, domestic and industrial life in Britain from 1783 to 1984 Graphmitre, Tavistock, Devon.
- Tristan, Flora (1840) Promenades Dans Londres. Trans. Palmer, D, and Pincetl, G. (1980) Flora Tristan's London Journal, A Survey of London Life in the 1830s George Prior, Publishers, London. Extract Worse than the slave trade in Appendix 1, Barty-King, H (1985).
- Peebles, Malcolm W. H. (1980) Evolution of the Gas Industry Macmillan, London and Basingstoke.

Development of Pacific coast oil gas process

1912. /Pintsch Railway oil Gas processes 1880s. Massive problems with lampblack created from the Pacific coast process. Up to 20 to 30 lb/1000 ft³ (300 to 500 g/m³) of oily soot. Major pollution problem leads to passage of early enviromental legislation at the state level.

Layout of a typical gas plant

- 1880s Coal gasification plant.
- 1910 CWG plant

Issues in gas processing

- Tar aerosols (tar extractors, condensers/scrubbers, Electrostatic precipitators in 1912)
- Light oil vapors (oil washing)
- Naphthalene (oil/tar washing)
- Ammonia gas (scrubbers)
- Hydrogen sulfide gas (purifier boxes)
- Hydrogen cyanide gas (purifier)

WWI-interwar era developments

- Loss of high quality gas oil (used as motor fuel) and feed coke (diverted for steelmaking) leads to massive tar problems. CWG tar is less valuable than coal gasification tar as a feed stock. Tar-water emulsions are uneconomical to process due to unsellable water and lower quality by products. :: CWG tar is full of lighter PAH's, good for making pitch, but poor in chemical precursors.
- Various "back-run" procedures for CWG generation lower fuel consumption and help deal with issues from the use of bitumious coal in CWG sets.
- Development of high pressure pipeline welding encourages the creation of large municipal gas plants and the consolidation of the MG industry. Sets the stage for rise natural gas.
- Electric lighting replaces gaslight. MG industry peak is sometime in mid 1920s
- 1936 or so. Development of Lurgi gasifier. Germans continue work on gasification/synfuels due to oil shortages.
- Public Utility Holding Company Act of 1935 forces break up of integrated coke and gas companies.
- Fischer-Tropff process for synthesis of liquid fuels from CO/H2 gas.
- Haber-Bosch ammonia process creates a large demand for industrial hydrogen.

Post WWII: the decline of manufactured gas

- Development of natural gas industry. NG is 37 MJ/m³
- Petrochemicals kill much of the value coal tar as a source of chemical feed stocks.(BTX, Phenols, Pitch)
- Decline in creosote use for wood preserving.
- Direct coal/natural gas injection reduces demand for metallurgical coke. 25 to 40% less coke is needed in blast furnaces.
- BOF and EAF processes obsolete cupola furnaces. Reduce need for coke in recycling steel scrap. Less need for fresh steel/iron.
- Steel is replaced with aluminum and plastics.
- Pthalic Anhydride production shifts from catalytic oxidation of naphthalene to o-xylol process.

Post WWII positive developments

- Catalytic upgrading of gas by use of hydrogen to react with tarry vapors in the gas
- The decline of coke making in the US leads to a coal tar crisis since coal tar pitch is vital for the production of carbon electrodes for EAF/Aluminum. US now has to import CT from china
- Development of process to make methanol via hydrogenation of CO/H2 mixtures.
- Mobil M-gas process for making gasoline from methanol
- SASOL coal process plant in South Africa.
- Direct hydrogenation of coal into liquid and gaseous fuels

Environmental effects

From its original development until the wide scale adoption of natural gas, more than 50,000 manufactured gas plants were in existence in the United States alone. The process of manufacturing gas usually produced a number of by-products that contaminated the soil and groundwater in and around the manufacturing plant, so many former town gas plants are a serious environmental concern, and cleanup and remediation costs are often high. MGPs were typically sited near or adjacent to waterways that were used for the discharge of wastewater contaminated with tar, ammonia and/or drip oils, as well as outright waste tars and tar-water emulsions. In the earliest days of MGP operations, coal tar was considered a waste and often disposed into the environment in and around the plant locations. While uses for coal tar developed by the late-1800s, the market for tar varied and plants that could not sell tar at a given time could store tar for future use, attempt to burn it as fuel for the boilers, or dump the tar as waste. The shift to the CWG process initially resulted in a reduced output of water gas tar as compared to the volume of coal tars. The advent of automobiles reduced the availability of naphtha for carburetion oil, as that fraction was desirable as motor fuel. MGPs that shifted to heavier grades of oil often experienced problems with the production of tar-water emulsions, which were difficult, time consuming, and costly to break. [The cause of tar-water emulsions is complex and was related to several factors, including free carbon in the carburetion oil and the substitution of bituminous coal as a feedstock instead of coke.] The production of large volumes of tar-water emulsions quickly filled up available storage capacity at MGPs and plant management often dumped the emulsions in pits, from which they may or may not have been later reclaimed. Even if the emulsions were reclaimed, the environmental damage from placing tars in unlined pits remained. The dumping of emulsions (and other tarry residues such as tar sludges, tank bottoms, and off-spec tars) into the soil and waters around MGPs is a significant factor in the pollution found at FMGPs today. Commonly associated with former manufactured gas plants (known as "FMGPs" in environmental remediation) are contaminants including:
- BTEX
- Diffused out from deposits of coal/gas tars
- Leaks of carburetting oil/light oil
- Leaks from drip pots, that collected condensible hydrocarbons from the gas
- Coal tar waste/sludge
- Typically found in sumps of gas holders/decanting ponds.
- Coal tar sludge has no resale value and so was always dumped.
- Volatile Organic Compounds
- Semi-volatile Organic Compounds
- Many heavier coal tar compounds are not very volatile, i.e PAHs
- Polycyclic aromatic hydrocarbons
- Found in copious quantities in coal tar, gas tar, and pitch.
- heavy metals
- Leaded solder for gas mains, lead piping, coal ashes.
- cyanide
- Purifier waste has large amounts of complex ferrocyanides in it.
- Lampblack
- Only found where crude oil was used as gasification feedstock.
- Tar emulsions

Town gas

Manufacturing process

2\ \mbox(s) + \mbox_2 \rightarrow 2\ \mbox

(Exothermic: Producer gas Reaction)

\mbox(s) + \mbox_2\mbox(g) \rightarrow \mbox + \mbox_2

(Endothermic: Water Gas Reaction)

\mbox+2\ \mbox_2\mbox\rightarrow \mbox_2+2\ \mbox_2

(Endothermic)

\mbox + \mbox_2\mbox \rightarrow \mbox_2 + \mbox_2

Early history of gas production by carbonization

Early history of gas production by gasification

The uses of gas and the later development of the gas industry

Historical References

Development of Pacific coast oil gas process

Layout of a typical gas plant

- 1880s Coal gasification plant.
- 1910 CWG plant

Issues in gas processing

WWI-interwar era developments

Post WWII: the decline of manufactured gas

Post WWII positive developments

Environmental effects

Water

:This article focuses on water as it is experienced in everyday life. See water (molecule) for information on the chemical and physical properties of pure water (H₂O, hydrogen oxide). Water (from the Old English word wæter; c.f German "Wasser", from PIE
- wod-or, "water") is a tasteless, odorless, and nearly colorless (it has a slight hint of blue) substance in its pure form that is essential to all known forms of life and is known also as the most universal solvent. Water is an abundant substance on Earth. It exists in many places and forms. It appears mostly in the oceans and polar ice caps, but also as clouds, rain water, rivers, freshwater aquifers, and sea ice. On the planet, water is continuously moving through the cycle involving evaporation, precipitation, and runoff to the sea. Water fit for human consumption is called potable water. This natural resource is becoming more scarce in certain places as human population in those places increases, and its availability is a major social and economic concern.

Molecular properties

Forms of water

potable water] Water takes many different shapes on earth: water vapor and clouds in the sky, waves and icebergs in the sea, glaciers in the mountain, aquifers in the ground, to name but a few. Through evaporation, precipitation, and runoff, water is continuously flowing from one form to another, in what is called the water cycle. Because of the importance of precipitation to agriculture, and to mankind in general, different names are given to its various forms: while rain is common in most countries, other phenomena are quite surprising when seen for the first time. Hail, snow, fog or dew are examples. When appropriately lit, water drops in the air can refract sunlight to produce rainbows. Similarly, water runoffs have played major roles in human history as rivers and irrigation brought the water needed for agriculture. Rivers and seas offered opportunity for travel and commerce. Through erosion, runoffs played a major part in shaping the environment providing river valleys and deltas which provide rich soil and level ground for the establishment of population centers. Water also infiltrates the ground and goes into aquifers. This groundwater later flows back to the surface in springs, or more spectacularly in hot springs and geysers. Groundwater is also extracted artificially in wells. Because water can contain many different substances, it can taste or smell very differently. In fact, humans and other animals have developed their senses to be able to evaluate the drinkability of water: animals generally dislike the taste of salty sea water and the putrid swamps and favor the purer water of a mountain spring or aquifer.

Water in biology

From a biological standpoint, water has many distinct properties that are critical for the proliferation of life that set it apart from other substances. Water carries out this role by allowing organic compounds to react in ways that ultimately allows replication. It is a good solvent and has a high surface tension, and thus allows organic compounds and living things to be transported in it. Fresh water has its greatest density at 4°C, then becoming less dense as it freezes or heats up from this point. As a stable, polar molecule prevalent in the atmosphere, it plays an important atmospheric role as an absorber of infrared radiation, crucial in the atmospheric greenhouse effect without of which, the average surface temperature would be −18° Celsius. Water also has an unusually high specific heat, which plays many roles in regulating global and regional climate, such as the Gulf Stream climate, allowing life to survive. Water is a very good solvent, chemically not unlike ammonia, and dissolves many types of substances, such as various salts and sugar, and facilitates their chemical interaction, which aids complex metabolisms. Some substances, however, do not mix well with water, including oils and other hydrophobic substances. Cell membranes, composed of lipids and proteins, take advantage of this property to carefully control interactions between their contents and external chemicals. This is facilitated somewhat by the surface tension of water. Water drops are stable due to the high surface tension of water caused by the strong intermolecular forces called cohesive forces. This can be seen when small quantities of water are put onto a nonsoluble surface such as polythene: the water stays together as drops. On extremely clean glass the water may form a thin film because the molecular forces between glass and water molecules (adhesive forces) are stronger than the cohesive forces. This property plays a key role in plant transpiration. A simple but environmentally important and unique property of water is that its common solid form, ice, floats on the liquid. This solid phase is less dense than liquid water, due to the geometry of the strong hydrogen bonds which are formed only at lower temperatures. For almost all other substances and for all other 11 uncommon phases of water ice except ice-XI, the solid form is more dense than the liquid form. Fresh water is most dense at 4°C, and will sink by convection as it cools to that temperature, and if it becomes colder it will rise instead. This reversal will cause deep water to remain warmer than shallower freezing water, so that ice in a body of water will form first at the surface and progress downward, while the majority of the water underneath will hold a constant 4°C. This effectively insulates a lake floor from the cold. While this behavior may seem obvious, even intuitive, it should be noted that almost all other chemicals are denser as solids than they are as liquids, and freeze from the bottom up. Life on earth has evolved with and adapted itself to the important features of water. The existence of abundant liquid, vapor and solid forms of water on Earth has been an important factor in the abundant colonization of Earth's various environments by life-forms adapted to those varying and often extreme conditions. Civilizations have historically flourished around rivers and major waterways; Mesopotamia, the so-called cradle of civilization, is situated between two major rivers. Large metropolises like London, Paris, New York, and Tokyo owe their success in part to their easy accessibility via water and the resultant expansion of trade. Islands with safe water ports, like Singapore and Hong Kong, have flourished for precisely this reason. In places such as North Africa and the Middle East, where water is scarcer, access to clean drinking water was and is a major factor in human development.

Astronomical position of Earth and impact on its water

Mesopotamia The coexistence of the solid, liquid, and gaseous phases of water on Earth is vital to the origin, evolution, and continued existence of life on Earth. However, if the Earth's location in the solar system were even marginally closer or further from the Sun (ie, a million miles or so), the conditions which allow the three forms to be present simultaneously would be far less likely to exist. Earth's mass allows gravity to hold an atmosphere. Water vapor and carbon dioxide in the atmosphere provides a greenhouse effect which helps maintain a relatively steady surface temperature. If Earth were less massive, a thinner atmosphere would cause temperature extremes preventing the accumulation of water except in polar ice caps (as on Mars). According to the solar nebula model of the solar system's formation, Earth's mass may be largely due to its distance from the Sun. The distance between Earth and the Sun and the combination of solar radiation received and the greenhouse effect of the atmosphere ensures that its surface is neither too cold nor too hot for liquid water. If Earth were more distant, most water would be frozen. If Earth were nearer to the Sun, its higher surface temperature would limit the formation of ice caps, or cause water to exist only as vapor. In the former case, the low albedo of oceans would cause Earth to absorb more solar energy. In the second case, a runaway greenhouse effect and inhospitable conditions similar to Venus would result. It has been proposed that life itself may maintain the conditions that have allowed its continued existence. The surface temperature of Earth has been relatively constant through geologic time despite varying solar flux, indicating that a dynamic process governs Earth's temperature via a combination of greenhouse gases and surface or atmospheric albedo. This proposal is known as the Gaia hypothesis.

Human uses of water

Gaia hypothesis All known forms of life depend on water. Water is a vital part of many metabolic processes within the body. Significant quantities of water are used during the digestion of food. (Note however that some bacteria and plant seeds can enter a cryptobiotic state for an indefinite period when dehydrated, and come back to life when returned to a wet environment) About 72% of the fat free mass of the human body is made of water. To function properly the body requires between one and seven litres of water per day to avoid dehydration, the precise amount depending on the level of activity, temperature, humidity, and other factors. It is not clear how much water intake is needed by healthy people. However, for those who do not have kidney problems, it is rather difficult to drink too much water, but (especially in warm humid weather and while exercising) dangerous to drink too little. People do often drink far more water than necessary while exercising, however, putting them at risk of water intoxication, which is frequently fatal. The "fact" that a person should consume eight glasses of water per day cannot be traced back to a scientific source. However, leading dieticians and nutritionists will tell you that this is the RDI (Recommended Daily Intake) of water. [http://ajpregu.physiology.org/cgi/content/full/283/5/R993]. The latest dietary reference intake report by the National Research Council recommended 2.7 liters of water total (including food sources) for women and 3.7 liters for men[http://www.iom.edu/report.asp?id=18495]. Water is lost from the body in urine and feces, through sweating, and by exhalation of water vapor in the breath. Humans require water that does not contain too much salt or other impurities. Common impurities include chemicals and/or harmful bacteria, such as crypto sporidium. Some solutes are acceptable and even desirable for perceived taste enhancement and to provide needed electrolytes.

Water as a precious resource

:See water resources for information about fresh water supplies. fresh water Because of the growth of world population and other factors, the availability of drinking water per capita is shrinking. The issue of water shortage can be solved through more production, better distribution and less waste of it. For this reason, water is a strategic resource for many countries. Many battles and wars, such as the Six-Day War in the Middle East, have been fought to gain access to it. Experts predict more trouble ahead because of the world's growing population, increasing contamination through pollution, and global warming. UNESCO's World Water Development Report (WWDR, 2003) from its World Water Assessment Program indicates that, in the next 20 years, the quantity of water available to everyone is predicted to decrease by 30%. 40% of the world's inhabitants currently have insufficient fresh water for minimal hygiene. More than 2.2 million people died in 2000 from diseases related to the consumption of contaminated water or drought. In 2004, the UK charity WaterAid reported that a child dies every 15 seconds due to easily preventable water-related diseases. Some have predicted that clean water will become the "next oil", making Canada, with this resource in abundance, possibly the richest country in the world.

Regulating water distribution

Drinking water is often collected at

Carbon monoxide

Toxicity

History

Chemistry

Carbon monoxide in the atmosphere

External links

Gas

Properties of a gas

Etymology

See also

Carbon

Notable characteristics

Applications

Other uses

History and Etymology

Allotropes

Occurrence

Organic compounds

Carbon chains

Carbon cycle

Isotopes

Precautions

References

See also

External links

Oxygen

Characteristics

Applications

History

Occurrence

Compounds

Isotopes

Precautions

See also

References

External links

Unburned hydrocarbon

Headline text

Town gas

Manufacturing process

Early history of gas production by carbonization

Early history of gas production by gasification

The uses of gas and the later development of the gas industry

Historical References

Development of Pacific coast oil gas process

Layout of a typical gas plant

Issues in gas processing

WWI-interwar era developments

Post WWII: the decline of manufactured gas

Post WWII positive developments

Environmental effects

See also

Town gas

Manufacturing process

Early history of gas production by carbonization

Early history of gas production by gasification

The uses of gas and the later development of the gas industry

Historical References

Development of Pacific coast oil gas process

Layout of a typical gas plant

Issues in gas processing

WWI-interwar era developments

Post WWII: the decline of manufactured gas

Post WWII positive developments

Environmental effects

See also

Water

Molecular properties

Forms of water

Water in biology

Astronomical position of Earth and impact on its water

Human uses of water

Water as a precious resource

Regulating water distribution