Ethyne (acetylene) (C₂H₂)

Ethyne (acetylene) (C₂H₂)

The first member of the homologous series of alkyne hydrocarbons.



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Ethyne, acetylene C₂H₂


Molar mass: 26.038 g/mol

Melting point: -84.7 °C

Boiling point: -80.8 °C

Density: 0.0010967 g/cm³

Relative steam density (air=1): 0.907

Heat of combustion: -1,301.1 kJ/mol


Ethyne, also known as acetylene, is a colourless, odourless, lighter-than-air gas. It dissolves in water weakly, but dissolves well in non-polar solvents. It explodes under pressure and breaks down into its elements, carbon and hydrogen, during an exothermic process. This is the reason why gas cylinders are filled with siliceous earth first, which is then impregnated with acetone, then acetylene is solved in this mixture.

Since it is highly unsaturated, acetylene is an extremely reactive compound.

It is also highly flammable and explosive. It burns with a sooty flame. Its typical reactions are addition and polymerisation.

It can be reduced to ethene and then to ethane with hydrogen addition. Vinyl-chloride can be produced with the addition of hydrogen-chloride; the end product of the polymerisation process is an important plastic, PVC.

Ethyne dissolved in liquid ammonia reacts with metallic sodium. During this reaction, hydrogen and sodium-carbide are formed. The salts of ethyne are called metal carbides.

Occurrence and production

Due to its high reactivity, ethyne does not occur in its free form in nature.

It is produced in a reaction of calcium-carbide and water in laboratories, and through the partial combustion of methane in industry.


Formerly it was used as fuel in carbide lamps. It is an important raw material in the chemical industry, but its importance has diminished for safety reasons, since it is highly explosive. Ethyne is used in welding and cutting torches. When mixed with oxygen, it burns with a flame hotter than 3,000 °C.



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Ethane (C₂H₆)

The second member in the homologous series of straight-chain alkanes.

Ethene (ethylene) (C₂H₄)

The first member in the homologous series of 1-alkenes.


Alkanes are saturated hydrocarbons which can be organised into a homologous series.

Benzene (C₆H₆)

Benzene is the simplest aromatic hydrocarbon.

Conformations of ethane

The staggered conformation of ethane is more stable than the eclipsed conformation.

Polymerisation of ethene

Polymerised ethylene is known as polyethylene, a type of plastic.

Oxygen (O₂) (intermediate)

A colourless, odourless gas, an important component of the atmosphere, indispensable to sustain terrestrial life.

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