First, physical properties
1, color: colorless
2, smell: tasteless
3. Melting point:-182.5℃
4. Boiling point:-16 1.5℃
5. Molecular structure: regular tetrahedral nonpolar molecules.
6. Molecular diameter: 0.4 1.4 nm.
7. Combustion heat: 890.438+0kJ/mol.
8. Relative density (water = 1): 0.42 (- 164℃)
Second, the chemical properties?
In general, methane is relatively stable and does not react with strong oxidants such as potassium permanganate, and does not react with strong acids and alkalis. However, under certain conditions, methane will also have some reactions.
1, substitution reaction
In the halogenation of methane, there are mainly chlorination and bromination. The reaction between methane and fluorine is exothermic. Once the reaction takes place, a lot of heat is difficult to remove, which destroys the generated fluoromethane and can only get carbon and hydrogen fluoride. Therefore, the direct fluorination reaction is difficult to realize and needs to be diluted with rare gas. The reaction between iodine and methane requires high activation energy, so the reaction is difficult. Therefore, iodine can not directly react with methane to produce methyl iodide. But its reverse reaction is easy to carry out.
Take chlorination as an example: it can be seen that the yellow-green gas of chlorine in the test tube gradually fades to produce white fog, and oily droplets are produced on the inner wall of the test tube, which are a mixture of methyl chloride, dichloromethane, chloroform (or chloroform), carbon tetrachloride (or carbon tetrachloride), hydrogen chloride and ethane (impurities) generated by the reaction of a small amount of methane with chlorine.
CH4+Cl2→ (illumination) CH3Cl (gas) +HCl
CH3Cl+Cl2→ (lighting) CH2Cl2 (oil) +HCl
CH2Cl2+Cl2→ (lighting) CHCl3 (oil) +HCl
CHCl3+Cl2→ (lighting) CCl4 (oil) +HCl
2. Oxidation reaction
The most basic oxidation reaction of methane is combustion:
CH4+2O2→CO2+2H2O
The hydrogen content of methane is the highest among all hydrocarbons, reaching 25%, so the gaseous hydrocarbons with the same mass are completely burned, and the oxygen consumption of methane is the highest.
3. Thermal decomposition
Under the condition of isolating air and heating to 1000℃, methane decomposes to produce carbon black and hydrogen.
CH4=( 1000℃)=C+2H2
Hydrogen is the raw material of synthetic ammonia and gasoline industry.
Extended data:
Main applications of methane:
Methane is a very important fuel and the main component of natural gas, accounting for about 87%. Methane is colorless and odorless at normal temperature and pressure. The special smell of domestic natural gas is an artificial smell added for safety, and methyl mercaptan or ethyl mercaptan is usually used. What is the boiling point of methane at atmospheric pressure? 16 1 Celsius.
As long as the gas content in the air exceeds 5% ~ 15%, it is very flammable. Liquefied methane will only burn under high pressure (usually 4 ~ 5 atmospheres). According to Chinese national standards, methane cylinders are brown and white.
Carbon black can be obtained by pyrolysis of methane, which can be used as an additive for pigments, inks, paints and rubber. Chloroform and carbon tetrachloride are both important solvents. Methane is widely distributed in nature and is one of the main components of natural gas, biogas and biogas. It can be used as fuel and raw material for producing hydrogen, carbon monoxide, carbon black, acetylene, hydrocyanic acid and formaldehyde.
The calorific value test of water heaters and gas stoves uses methane as the standard fuel. Production of combustible gas alarm standard gas and calibration gas. It can also be used as a carbon source for vapor chemical deposition of solar cells and amorphous silicon films. Methane is used as a raw material for medicine and chemical synthesis.
References:
Baidu encyclopedia-methane