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Methane
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Methane

 
 
 
 
 
 

 
 
 
 
 
 
 

 
 
 
 
 
 
 
 
 
 
 
 
 

Properties

General

Name Methane
Lewis Structure:
    H  
    |  
  H-C-H
    |  
    H  
Chemical formula CH4
Formula weight 16.04 amu
Synonyms Marsh gas; Methyl hydride
CAS number 74-82-8

Phase behavior

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
ΔvapH; 8.17 kJ/mol
Gas properties

ΔfH0gas; -74.87 kJ/mol
S0gas 188 J/mol·K
Cp 35.69 J/mol·K

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 point -188°C
Autoignition temperature 600°C
Explosive limits 5-15%

More info

Properties NIST WebBook
MSDS Hazardous Chemical Database
SI units were used where possible. Unless otherwise stated, standard conditions were used.

Disclaimer and references

The simplest hydrocarbon, methane is a gas with a chemical formula of CH4.

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

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:
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

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.

See also

Alkanes
  methane
CH4
|
 
ethane
C2H6
|
 
propane
C3H8
|
 
butane
C4H10
|
 
pentane
C5H12
|
 
hexane
C6H14
|
 
heptane
C7H16
|
 
octane
C8H18
|
 
nonane
C9H20
|
 
decane
C10H22
|
 
undecane
C11H24