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Names | |
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Preferred IUPAC name | |
Systematic IUPAC name
Ethyne[3] | |
Identifiers | |
3D model (JSmol)
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906677 | |
ChEBI | |
ChEMBL | |
ChemSpider | |
ECHA InfoCard | 100.000.743 |
EC Number |
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210 | |
KEGG | |
PubChem CID
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RTECS number |
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UNII | |
UN number | 1001 (dissolved) 3138 (in mixture with ethylene and propylene) |
CompTox Dashboard (EPA)
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Properties | |
C2H2 | |
Molar mass | 26.038 g·mol−1 |
Appearance | Colorless gas |
Odor | Odorless |
Density | 1.1772 g/L = 1.1772 kg/m3 (0 °C, 101.3 kPa)[4] |
Melting point | −80.8 °C (−113.4 °F; 192.3 K) Triple point at 1.27 atm |
−84 °C; −119 °F; 189 K (1 atm) | |
slightly soluble | |
Solubility | slightly soluble in alcohol soluble in acetone, benzene |
Vapor pressure | 44.2 atm (20 °C)[5] |
Acidity (pKa) | 25[6] |
Conjugate acid | Ethynium |
−20.8×10−6 cm3/mol [7] | |
Thermal conductivity | 21.4 mW·m−1·K−1 (300 K) [7] |
Structure | |
Linear | |
Thermochemistry[7] | |
Heat capacity (C)
|
44.036 J·mol−1·K−1 |
Std molar
entropy (S⦵298) |
200.927 J·mol−1·K−1 |
Std enthalpy of
formation (ΔfH⦵298) |
227.400 kJ·mol−1 |
Gibbs free energy (ΔfG⦵)
|
209.879 kJ·mol−1 |
Std enthalpy of
combustion (ΔcH⦵298) |
1300 kJ·mol−1 |
Hazards | |
GHS labelling: | |
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Danger | |
H220, H336 | |
P202, P210, P233, P261, P271, P304, P312, P340, P377, P381, P403, P405, P501 | |
NFPA 704 (fire diamond) | |
300 °C (572 °F; 573 K) | |
Explosive limits | 2.5–100% |
NIOSH (US health exposure limits): | |
PEL (Permissible)
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none[5] |
REL (Recommended)
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C 2500 ppm (2662 mg/m3)[5] |
IDLH (Immediate danger)
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N.D.[5] |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Acetylene (systematic name: ethyne) is the chemical compound with the formula C2H2 and structure H−C≡C−H. It is a hydrocarbon and the simplest alkyne.[8] This colorless gas is widely used as a fuel and a chemical building block. It is unstable in its pure form and thus is usually handled as a solution.[9] Pure acetylene is odorless, but commercial grades usually have a marked odor due to impurities such as divinyl sulfide and phosphine.[9][10]
As an alkyne, acetylene is unsaturated because its two carbon atoms are bonded together in a triple bond. The carbon–carbon triple bond places all four atoms in the same straight line, with CCH bond angles of 180°.[11]
The name acetylene is retained for the compound HC≡CH. It is the preferred IUPAC name, but substitution of any kind is not allowed; however, in general nomenclature, substitution is allowed, for example fluoroacetylene [fluoroethyne (PIN)], but not by alkyl groups or any other group that extends the carbon chain, nor by characteristic groups expressed by suffixes.