Main Page | See live article | Alphabetical index 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   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 This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License.