H₂
Compound · Gas
Hydrogen
氢气
Hydrogen (氢气), formula H₂, is a gas with a molar mass of 2.02 g/mol (CAS 1333-74-0). Colourless odourless gas of very low density; poorly soluble in water.
Key facts
| Molar mass | 2.02 g/mol |
|---|---|
| Category | Gas |
| State at 25°C | Gas |
| CAS | 1333-74-0 |
Structure
H–H
Lightest diatomic molecule
Physical properties
| Appearance | Colourless odourless gas of very low density |
|---|---|
| Melting point | −259 °C |
| Boiling point | −253 °C |
| Density | 0.09 g/L (气体) |
| Solubility | Poorly soluble in water |
Key reactions
2H₂ + O₂ →(点燃) 2H₂O
Burns to water; a clean energy source
H₂ + Cl₂ →(点燃) 2HCl
Combines with chlorine
CuO + H₂ →(Δ) Cu + H₂O
Reduces metal oxides
Main uses
- Ammonia synthesis and petroleum hydrogenation
- Fuel cells and clean fuel
- Metallurgical reductant
Hazard
ModerateHighly flammable; mixtures with air explode on ignition
Constituent elements
Data sources
Molar mass is computed from IUPAC (CIAAW) standard atomic weights; formula, properties and reactions can be verified on PubChem, NIST and Wikipedia. The CAS number is the substance's unique registry identifier. Educational reference only.