Nitrogen dioxide

**Properties**
General
Name	Nitrogen dioxide
Chemical formula	N O₂
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
Δ_fH⁰_gas	kJ/mol
Δ_fH⁰_liquid	kJ/mol
Δ_fH⁰_solid	kJ/mol
S⁰_{gas, 1 bar}	J/mol·K
S⁰_{liquid, 1 bar}	J/mol·K
S⁰_solid	J/mol·K
Safety
Ingestion
Inhalation
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 and smells rather disgustingly (biting), though characteristical. It is poisonous.

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

2 NO + O₂ --> NO₂

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

It reacts, even at normal temperature & pressure, with water, 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