Nitrogen dioxide

Properties General Name Nitrogen dioxide Chemical formula NO2 Appearance brown/orange gas Physical Formula weight 46.01 amu Melting point -263.85 K (9.3 °C) Boiling point -252.00 K (21.15 °C) Density   Crystal structure   Solubility   Thermochemistry ΔfH0gas   kJ/mol ΔfH0liquid   kJ/mol ΔfH0solid   kJ/mol S0gas, 1 bar   J/mol·K S0liquid, 1 bar   J/mol·K S0solid   J/mol·K Safety Ingestion   Inhalation Deadly poison! Insidious. Can cause lung edema or death after several days delay. 100 ppm dangerous, 200 ppm may be lethal for short exposures. Skin   Eyes   More info SI units were used where possible. Unless otherwise stated, standard conditions were used. Disclaimer and references

The chemical compound nitrogen dioxide is an orange/brown gas with a characteristic sharp, biting odor. It is considered an insidious deadly poison by inhalation.

Nitric oxide (NO) spontaneously produces the dioxide when exposed to air:

2 NO + O₂ --> 2NO₂

It is also generated by various nitric acid reactions, e.g. when metals, such as copper or silver, are exposed to nitric acid.

It reacts readily with water, even at normal temperature and pressure, where it disproportionates to nitric and nitrous acid. That reaction is used in the Ostwald process.

Vapor pressure, mmHg: 400 @ 80 oC
Vapor density (air=1): 1.58
Specific gravity/density: 1.4494 at 20°C
Solubility in water: Reacts
Odor threshold: 2.0 mg/m3
Heat of vaporization: 9.110 kcal/mole