Acetylene
| Names | |
|---|---|
| Preferred IUPAC name
Acetylene | |
| Systematic IUPAC name
Ethyne | |
| Identifiers | |
3D model (JSmol) |
|
| 906677 | |
| ChEBI | |
| ChEMBL | |
| ChemSpider | |
| ECHA InfoCard | 100.000.743 |
| EC Number |
|
| 210 | |
| KEGG | |
PubChem CID |
|
| RTECS number |
|
| 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) |
| 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) |
| Acidity (pKa) | 25 |
| Conjugate acid | Ethynium |
| −20.8×10−6 cm3/mol | |
| Thermal conductivity | 21.4 mW·m−1·K−1 (300 K) |
| Structure | |
| Linear | |
| Thermochemistry | |
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: | |
| 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) |
none |
REL (Recommended) |
C 2500 ppm (2662 mg/m3) |
IDLH (Immediate danger) |
N.D. |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references | |
Acetylene (systematic name: ethyne) is a chemical compound with the formula C2H2 and structure HC≡CH. It is a hydrocarbon and the simplest alkyne. 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. Pure acetylene is odorless, but commercial grades usually have a marked odor due to impurities such as divinyl sulfide and phosphine.
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°. The triple bond in acetylene results in a high energy content that is released when acetylene is burned.