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General |
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| Name | Methane |
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Lewis Structure:
H
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H-C-H
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H
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| Chemical formula | C H4 |
| Formula weight | 16.04 amu |
| 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 K (-162°C) |
| Triple point | 90.67 K (-182.48°C) 0.117 bar |
| Critical point | 190.6 K (-82.6°C) 46 bar |
| ΔfusH | 1.1 kJ/mol |
| ΔvapHThe heat of vaporization is a physical property of substances. It is defined as the heat required to vaporize one mole of a substance at its boiling point under standard pressure (101325 Pa). The heat of vaporization is expressed in kJ/mol. The use of kJ/ | 8.17 kJ/mol |
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Gas properties |
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| ΔfH0gasThe standard enthalpy of formation of a compound is the change of enthalpy that accompanies the formation of 1 mole of that substance from its component elements, at their standard states (the most stable form of the element or compound at 25 degrees Cels | -74.87 kJ/mol |
| S0gasIn chemistry, the standard molar entropy is the entropy content of one mole of substance, under conditions of standard temperature and pressure. By comparing the entropies of products and reactants in a chemical reaction, we can determine whether the reac | 188 J/mol·K |
| CpHeat capacity (abbreviated C or just C also called thermal capacity is the ability of matter to store heat. The heat capacity of a certain amount of matter is the quantity of heat (measured in Joules) required to raise its temperature by one kelvin. The S | 35.69 J/mol·K |
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Safety | |
| 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 pointThe flashpoint of a fuel is the lowest temperature at which it can form an ignitable mix with air. At this temperature the vapour may cease to burn when the source of ignition is removed. A slightly higher temperature, the fire point, is defined at which | -188°C |
| Autoignition temperatureA substance's autoignition temperature is the lowest temperature at which it will burst into flame in air, even without an external spark or other source of ignition. The lowest temperature at which a substance will ignite in the presence of an external s | 600°C |
| Explosive limitThe explosive limit of a gas or a vapour, is the limiting concentration (in air) that is needed for the gas to ignite and explode. There are two explosive limits for any gas or vapor, the lower explosive limit LEL and the upper explosive limit UEL . At cos | 5-15% |
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More info | |
| Properties | NIST WebBook |
| MSDS | Hazardous Chemical Database |
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SI units were used where possible. Unless otherwise stated, standard conditions were used. Disclaimer and references
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The simplest hydrocarbon, methane, is a gas with a chemical formula of C H4.
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):
Due to the heat and attack by the active species , the methane reacts 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:
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.
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.
The strength of the carbon- 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.
Pure methane is odorless, but when used as a fuel is usually mixed with small quantities of strongly-smelling sulfur compounds such as ethyl mercaptan to enable the detection of leaks.
Methane is a greenhouse gas with a global warming potential of 21 (meaning that it has 21 times the warming ability of carbon dioxide).
Methane results from the decomposition of certain organic matters in the absence of oxygen. It is therefore also classified as a biogas.
Principal sources are
80% of the world emissions are of human source. 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.
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 is 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.
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