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Methane, the chemical formula CH, is the simplest hydrocarbon composed of one carbon and four hydrogen atoms by sp hybridization. Introduction of Methane and Properties

Structure of Methane Molecule

Therefore, the structure of the Methane molecule is a regular tetrahedral structure, and the bond lengths of the four bonds are equal to the same bond angle.

Methane

Methane is a colorless, odorless gas under standard conditions. The biogas produced when some organic matter is decomposed in the absence of oxygen is actually methane.

In theory, the bond line of methane can be expressed as a dot “·”, but it has not been seen in practice.

The reason may be that the “·” sign can also represent electrons. So in the middle school stage, methane is considered to have no key line.

Methane is mainly used as a fuel, such as natural gas and gas, and is widely used in civil and industrial applications.

As a chemical raw material, it can be used to produce acetylene, hydrogen, synthetic ammonia, carbon black, nitrochloromethane, carbon disulfide, methyl chloride, dichloromethane, chloroform, carbon tetrachloride, and hydrocyanic acid.

Methane Properties and Reactions

Under normal circumstances, methane is relatively stable, does not react with strong oxidants such as potassium permanganate, and does not react with strong acids and bases. However, under certain conditions, some reactions occur in methane.

Substitution reaction

Among the halogenation of methane, there are mainly chlorination and bromination. The reaction between methane and fluorine is a large amount of exothermic.

Once the reaction occurs, a large amount of heat is difficult to remove, destroying the generated fluoromethane, and only carbon and hydrogen fluoride are obtained.

Therefore, the direct fluorination reaction is difficult to achieve and needs to be diluted with a rare gas.

The reaction of iodine with methane requires higher activation energy and the reaction is difficult to carry out.

Methane

Therefore, iodine cannot be directly substituted with methane to form methyl iodide. But its reverse reaction is easy to carry out.

Taking chlorination as an example: it can be seen that the yellow-green gas of chlorine in the test tube gradually fades, a white mist is formed, and oil droplets are formed on the inner wall of the test tube, which is the methyl chloride and dichloride formed by the reaction of methane and chlorine. Introduction of Methane and Properties

A mixture of methane, chloroform (or chloroform), carbon tetrachloride (or tetrachloromethane), hydrogen chloride, and a small amount of ethane (impurities).

CH+Cl→(light)CHCl(gas)+HCl

CHCl+Cl→(light)CHCl (oil)+HCl

CHCl2+Cl→(light)CHCl (oil)+HCl

CHCl+Cl→(light)CCl(oil)+HCl

The liquid level in the test tube rises, and white crystals in the saline solution are precipitated, which is because the hydrogen chloride generated in the reaction is dissolved in water.

Because hydrogen chloride is very soluble in water, it dissolves in water and increases the concentration of chloride ions in the water to precipitate sodium chloride crystals.

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Hold the tube mouth with your thumb, raise the liquid level, and press the tube up. Add purple pistil test solution or zinc particles to the test tube to verify that it is dilute hydrochloric acid.

If the amount of chlorine is controlled, a large amount of methane is used to obtain mainly methyl chloride; if a large amount of chlorine is used, carbon tetrachloride is mainly obtained.

Industrially, the rectification is carried out to separate the mixtures one by one. The above several chlorinated products are important solvents and reagents.

Features:

1 does not react in the dark at room temperature.

2 reacted at 2500C.

3 can react under the action of light at room temperature.

4 using light to initiate the reaction, the absorption of a photon can produce thousands of molecules of methyl chloride.

5 If there is oxygen or some impurities that can capture free radicals, the reaction has an induction period, and the length of the induction period is related to the presence of these impurities.

According to the characteristics of the above facts, it can be judged that the chlorination of methane is a radical type substitution reaction.

Oxidation reaction

The most basic oxidation reaction of methane is combustion:

CH+2O→CO+2HO

The hydrogen content of methane is the highest among all hydrocarbons, reaching 25%, so the same quality of gaseous hydrocarbons is completely burned, and methane has the highest oxygen consumption. Introduction of Methane and Properties

Methane

Ignite pure methane, cover a dry beaker over the flame, and quickly see the condensation of water vapor on the beaker wall.

Invert the beaker, add a small amount of clarified lime water, shake, and the lime water becomes cloudy. It indicates that methane is burned to produce water and carbon dioxide.

Collect methane gas in a high glass cylinder, stand upright on the table, remove the glass piece, and quickly put the burning spoon with the burning candle into the tube, the candle will be extinguished immediately, but the methane is burning in the bottle mouth.

Light blue flame. This means that methane can burn quietly in the air but does not support combustion. Divide 2/3 of the oxygen from the oxygen storage tank with a large test tube and then add 1/3 volume of methane.

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Plug it with a rubber stopper and take out the water. The tube was inverted several times to allow the gas to mix thoroughly.

Use a cloth to bake the tube outside, let the tube mouth tilt down slightly, remove the stopper, and quickly ignite the tube with the burning small wooden strip, that is, a sharp popping sound occurs.

Although this experiment is simple, it is easy to fail. The methane released from the glass conduit is ignited and placed in a bottle filled with chlorine. Introduction of Methane and Properties

The methane will continue to burn, emitting a red-yellow flame while seeing black smoke and white mist.

Black smoke is carbon black, and white mist is a hydrochloric acid mist formed by hydrogen chloride gas and water vapor.

Heat decomposition

Methane decomposes to form carbon black and hydrogen under the condition of insulating air and heating to 1000 °C

CH= (1000°C)=C+2H

Hydrogen is a raw material for industries such as ammonia and gasoline; carbon black is a raw material for the rubber industry.

Hydrate formation

Methane can form caged hydrates, and methane is encased in “cage”. This is the flammable ice we often say.

It is an ice-like, non-stoichiometric, composed of water and natural gas mixed under medium and high-pressure conditions under certain conditions (suitable temperature, pressure, gas saturation, water salinity, pH, etc.) Cage-like crystal compound (carbon has a large electronegativity, and under high pressure, it can attract hydrogen atoms similar to each other to form a hydrogen bond to form a cage structure).

It can be represented by m CH4 ·nH2O , m represents a gas molecule in the hydrate, and n is a hydration index (ie, the number of water molecules).

Combustible ice is mainly stored in the permafrost zone on the seabed or in cold regions and is difficult to find and explore. Introduction of Methane and Properties

The newly developed highly sensitive instrument can instantly measure the accurate content of various ultra-methane, ethane, propane, and hydrogen in the seabed soil and rock, and judge the existence and resources of combustible ice resources and resources. Indicators.

Greenhouse_effect

Natural gas hydrates having a methane content of more than 99% are also referred to as methane hydrates.

Greenhouse effect

On April 2, 2018, researchers at the US Department of Energy’s Lawrence Berkeley National Laboratory used the comprehensive observations of the Earth’s atmosphere obtained from the Observatory of the Great Southern Plains of Oklahoma for the first time to directly prove that methane causes the earth’s surface greenhouse. The effect continues to increase.

What is the greenhouse effect?

Researchers say that at the beginning of the 21st century, the concentration of methane in the atmosphere stagnated, and the greenhouse effect followed the same pattern; but since 2007, when the concentration of methane began to rise, the greenhouse effect caused by it also rose.

Main application

Methane is a very important fuel and is the main component of natural gas, accounting for about 87%.

Methane is colorless and odorless in a standard pressure room temperature environment; the special taste of domestic natural gas is an artificial odor added for safety, usually using methyl mercaptan or ethanethiol.

Methane

In an atmospheric pressure environment, the boiling point of methane is −161 °C. The gas content in the air is very flammable as long as it exceeds 5% to 15%.

Liquefied methane does not burn unless it is in a high-pressure environment (usually 4 to 5 atmospheres). According to Chinese national standards, methane cylinders are brown and white.

The pyrolysis of methane can be used to obtain carbon black, which is used as an additive for pigments, inks, paints, and rubber; chloroform and CCl4 are important solvents.

Methane is widely distributed in nature and is one of the main components of natural gas, biogas and pit gas. Introduction of Methane and Properties

It can be used as a fuel and as a raw material for the production of hydrogen, carbon monoxide, carbon black, acetylene, hydrocyanic acid, and formaldehyde.

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Methane is used as a standard fuel for heat value testing of water heaters and gas stoves. Production of standard gas for flammable gas alarms, calibration gas.

It can also be used as a carbon source for solar cells, vapor phase chemical deposition of amorphous silicon films. And methane is used as a raw material for the production of pharmaceutical and chemical synthesis.

In addition to fuel, it is widely used in the synthesis of ammonia, urea, and carbon black, and can also be used to produce methanol, hydrogen, acetylene, ethylene, formaldehyde, carbon disulfide, nitromethane, hydrocyanic acid, and 1,4-butanediol.

Chlorination of methane yields mono-, di-, trichloromethane, and carbon tetrachloride.