Properties
|
General
|
| Name |
Nitrogen dioxide |
| Chemical formula |
NO2 |
| Appearance |
brown/orange gas |
|
Physical
|
| Formula weight |
46.01 amu |
| Melting point |
see dinitrogen tetroxide |
|
| Boiling point |
see dinitrogen tetroxide |
| Density |
1.58 (air = 1) |
| Specific gravity |
1.4494 at 20°C |
| Crystal structure |
|
| Vapor pressure |
400 mmHg at 80°C |
| Solubility |
Reacts with water |
|
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 |
| Heat of vaporization |
9.110 kcal/mole |
|
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 |
Odor threshold: 2.0 mg/m³ |
|
SI units were used where possible. Unless otherwise stated, standard conditions were used.
Disclaimer and references
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The chemical compound nitrogen dioxide (NO2) is a red or 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, which in turn allows the industrial production of fertilizers and explosives.
Red fuming nitric acid has a certain percentage of dissolved nitrogen dioxide, hence its red color.
Nitrogen dioxide is in constant equilibrium with dinitrogen tetroxide.
2NO2 <-> N2O4
This reaction is pushed towards dinitrogen tetroxide as temperatures go down. Nitrogen dioxide rarely exists as a liquid or solid because almost all of it will be converted to dinitrogen tetroxide.
Nitrogen dioxide is one of the most prominent air pollutants. Long-term exposure to concentration levels above 40-100 microgram/m³ causes adverse health effects (http://www.euro.who.int/document/e79097.pdf). From a health point of view, the most important source of nitrogen dioxide is road traffic, emitting nitrogen oxides very near people and causing levels of concern in streets and cities, including exceedances of European limit values. The picture below, depicting results of satelite measurements, illustrates nitrogen dioxide as large scale pollutant, with rural background ground level concentrations in some areas around 30 microgram/m³, not far below unhealthy levels. Nitrogen dioxide plays a crucial role in atmospheric chemistry, including the formation of tropospheric ozone.
Missing imageNO2_pollution_europe_hires.jpg NO 2 pollution levels in Europe. de:Stickstoffdioxid
fr:Dioxyde d'azote
it:Diossido di azoto
sk:Oxid dusičitý
zh:二氧化氮
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