Methane? |
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Structure of Methane |
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General |
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| Name | Methane |
H
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H-C-H
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H
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| Chemical formula | CH4 |
| Formula weight | 16.04 u |
| Synonyms | Marsh gas; Methyl hydride |
| CAS number | 74-82-8 |
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Phase behavior |
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| Melting point | 90.6 K (−182.5 °C) |
| Boiling point | 111.55 K (−161.6 °C) |
| Triple point | 90.67 K (−182.48 °C) 11.7 kPa |
| Critical point | 190.6 K (−82.6 °C) 4.6 MPa |
| ΔfusH | 1.1 kJ/mol |
| ΔvapH | 8.17 kJ/mol |
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Gas properties |
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| ΔfH0gas | −74.87 kJ/mol |
| ΔfG0gas | −50.828 kJ/mol |
| S0gas | 188 J/(mol·K) |
| Cp | 35.69 J/(mol·K) |
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Safety |
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| Acute effects | Asphyxia; in severe cases unconsciousness, cardiac arrest or CNS injury. The compound is transported as a cryogenic liquid; exposure to this will obviously cause frostbite. |
| Chronic effects | ??? |
| Flash point | −188 °C |
| Autoignition temperature | 600 °C |
| Explosive limits | 5-15% |
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More info |
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| Properties | NIST WebBook |
| MSDS | Hazardous Chemical Database |
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SI units were used where possible. Unless otherwise stated, standard conditions were used. |
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The simplest hydrocarbon, methane, is a gas with a chemical formula of CH4. Pure methane is odorless, but when used commercially is usually mixed with small quantities of strongly-smelling sulfur compounds such as ethyl mercaptan to enable the detection of leaks.
A principal component of natural gas, methane is a significant fuel. Burning one molecule of methane in the presence of oxygen releases one molecule of CO2 (carbon dioxide) and two molecules of H2O (water):
- CH4 + 2O2 → CO2 + 2H2O
Methane is a greenhouse gas with a global warming potential of 21.
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Contents |
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Sources of methane
Animal flatulation accounts for 17% of global methane emissions. A single cow is estimated to produce 600 litres of methane every dayPrincipal methane sources are
- Outgassing from earth's mantle through mud volcanoes
- decomposition of organic wastes
- natural sources (marshes): 23 %
- mineral fuel extraction: 20 %, see Coal bed methane extraction
Methane reacts with oxygen in volcanic areas and become carbon dioxide. Methane is extracted from geological deposits as a mineral fuel which is associated with other hydrocarbon fuels sometimes accompanied by helium and nitrogen.
- the processes of digestion in animals (cattle): 17 %
- bacteria found in rice plantations: 12 %
- biomass anaerobic heating or combustion
60% of the world emissions are from sources affected by humans. They come primarily from agricultural and other human activities. During the past 200 years, the concentration of this gas in the atmosphere doubled, passing from 0.8 to 1.7 ppm by volume.
Methane is also classified as a biogas because it can be created by the (anaerobic) decomposition of certain organic matters.
- Industrial sources
Methane can be created and used industrially, and perhaps in nature, by chemical reactions such as the Sabatier process, Fischer-Tropsch process, and steam reforming. Similar gases and materials are often present in geologic and volcanic processes.
- At high pressures, such as are found on the bottom of the ocean, methane forms a solid clathrate with water. An unknown but possibly very large quantity of methane is trapped in this form in ocean sediments. The sudden release of large volumes of methane from such sediments into the atmosphere has been suggested as a possible cause for rapid global warming events in the earth's distant past, such as the Paleocene-Eocene thermal maximum of 55 million years ago.
- One source estimates the size of the methane deposits of the oceans at ten thousand billion tons. (BBC Horizon: Global Dimming) Theories suggest that should global warming cause them to heat up sufficiently, all of this methane could again be suddenly released into the atmosphere. Since methane is eight times stronger than CO2 as a greenhouse gas, this would immensely magnify the greenhouse effect, heating Earth to unprecedented levels.
Reactions of methane
In the combustion of methane several steps are involved:
Methane forms to a methyl radical (CH3), which reacts to formaldehyde (HCHO or H2CO). The formaldehyde reacts to a formal radical (HCO), which then forms carbon monoxide (CO). The process is called oxidative pyrolysis:
- CH4 + O2 → CO + H2 + H2O
Following oxidative pyrolysis, the H2 oxidizes, forming H2O, replenishing the active species, and releasing heat. This occurs very quickly, usually in less than a millisecond.
- H2 + ½ O2 → H2O
Finally, the CO oxidizes, forming CO2 and releasing more heat. This process is generally slower than the other chemical steps, and typically requires a few to several milliseconds to occur.
- CO + ½ O2 → CO2
- Hydrogen activation
The strength of the carbona href="Hydrogen.html" title="Hydrogen">hydrogen covalent bond in methane is among the strongest in all hydrocarbons, and thus its use as a chemical feedstock is limited. The search for catalysts which can facilitate C-H bond activation in methane and other low alkanes is an area of research with considerable industrial significance.
Extraterrestrial Methane
Methane has been detected or is believed to exist in several locations of the solar system. It is believed to have been created by abiotic processes, with the possible exception of Mars.
Traces of methane gas are present in the thin atmosphere of the Earth's Moon.
Methane has also been detected in interstellar clouds.
Methane on Earth
Methane is used in industrial chemical processes and may be transported in liquid or refrigerated liquid form. While leaks from a liquid container are initially heavier than air, the gas is lighter than air. Gas pipelines distribute large amounts of natural gas, of which methane is a significant component.
Methane is typically found on Earth, when not in gas deposits, in methane hydrate deposits under high pressure under deep abyssal plains of oceans, ostensibly forming from the decay of sinking biotic materials at shallow levels, but reworking by deep hot biosphere that needs methane outgassing from earth's mantle. Methane practically explains all process of carbon geochemical cycle and important geological processes. Methane's effect as a greenhouse gas is twenty times greater than carbon dioxide. It is possible that major extinction in the history of the earth is due to methane. During the breakup of supercontinent Pangaea in the Triassic Period, an enormous volume of methane was released to the atmosphere. Methane reacts with oxygen yielding carbon dioxide in magmatic volcanoes. Methane reacts with oxygen and calcium forming carbonate cements in sedimentary reservoirs with petroleum. Methane feeds bacterial ecosystems, chemosynthetic communities and deep-water corals that live on the ocean floor. Methane is the main gas that is released by mud volcanoes, eventually accompanied by helium, nitrogen and brines with bromine, iodine and liquid bitumen. Methane displacement at great depths may be a cause of earthquakes. Methane can polymerize by Fischer-Tropsch synthesis forming gas to liquids natural hydrocarbons in earth's mantle or through serpentinization of peridotites that yield hydrogen in presence of catalyst metals such as nickel, iron, and form natural petroleum. Methane acts on organic rich shales and produces a minor contribution (1-3%) to form petroleum with true biomarkers as hopanoids and others insaturated hydrocarbons (n-alkenes). Methane interacts with peats, forming coal and bearing mercury, nickel, arsenic,cadmium, selenium, vanadium, uranium and other toxic metals. Methane has a wide range of thermodynamic stability. Methane flares can be a cause of aerial disasters.
Units of measure
- One cubic meter (m³) at normal pressure (101.3 kPa) has a mass of 717 grams.
Methane in heraldry
A methane molecule appears in the arms of Hoerskool Secunda.1
See also
- alkane, a type of hydrocarbon of which methane is simplest member.
- methane clathrate, form of water ice which contains methane.
- methanogen, archaea that produce methane as a metabolic by-product.
- methanogenesis, the formation of methane by microbes.
- methanotroph, bacteria that are able to grow using methane as their only source of carbon and energy.
- methyl group, a functional group similar to methane
External links
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methane |
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ethane |
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propane |
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butane |
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pentane |
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hexane |
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heptane |
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octane |
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nonane |
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decane |
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undecane |
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dodecane |
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tridecane |
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tetradecane |
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pentadecane |
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hexadecane |
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heptadecane |
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octadecane |
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nonadecane |
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eicosane |
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heneicosane |
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docosane |
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tricosane |
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tetracosane |
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pentacosane |
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hexacosane |
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heptacosane |
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octacosane |
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nonacosane |
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triacontane |
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hentriacontane |
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dotriacontane |
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tritriacontane |
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tetratriacontane |
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pentatriacontane |
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hexatriacontane |
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