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Nitrous oxide



Name Dinitrogen oxide
Chemical formula N2O
Appearance Colourless gas


Formula weight 44.0 amu
Melting point 182 K (-91 °C)
Boiling point 185 K (-88 °C)
Density 1.2 ×103 kg/m3 (liquid)
Solubility 0.112 g in 100g water


ΔfH0gas 82.05 kJ/mol
ΔfH0liquid ? kJ/mol
ΔfH0solid ? kJ/mol
S0gas, 1 bar 219.96 J/mol·K
S0liquid, 1 bar ? J/mol·K
S0solid ? J/mol·K


Inhalation See main text. May cause asphyxiation without warning.
Skin Hazardous when cryogenic or compressed.
Eyes Hazardous when cryogenic or compressed.
More info Hazardous Chemical Database
SI units were used where possible. Unless otherwise stated, standard conditions were used.

Disclaimer and references

Nitrous oxide, also known as dinitrogen oxide or dinitrogen monoxide, is a chemical compound with chemical formula N2O. Under room conditions it is a colourless non-flammable gas, with a pleasant slightly sweet odor. It is commonly known as laughing gas for the exhilarating effects of inhaling it. It is used in surgery and dentistry for its anaesthetic effects.

The structure of the nitrous oxide molecule is a linear chain of a nitrogen atom bound to a second nitrogen, which in turn is bound to an oxygen atom. It is a resonance structure of

Nitrous oxide N2O should not be confused with nitric oxide NO and nitrogen dioxide NO2.

The gas was discovered by Joseph Priestley in 1772; Humphry Davy in the 1790s tested the gas on himself and some of his friends (including the poets Samuel Taylor Coleridge and Robert Southey). They soon realised that nitrous oxide considerably dulled the sensation of pain, even if the inhaler were still semi-conscious, and so it came into use as an anaesthetic, particularly by dentists.

There have been examples of abuse of nitrous oxide for its euphorient effects. The fear of staff abusing the gas is the main reason that it is rarely used today. While the gas itself is not toxic, death can result if it is inhaled in such a way that not enough oxygen is breathed in, especially if the user becomes unconscious. Long-term use in large quantities has been associated with symptoms similar to vitamin B12 deficiency: anemia and neuropathy.

What about the legality of inhaling the gas for recreational use?

The gas is licensed for use as a food additive, specifically as an aerosol propellant. Its most common use in this context is in aerosol whipped cream.

The gas is excellently soluble in fatty compounds. In aerosol whipped cream, it is dissolved in the fatty cream until it leaves the can, when it becomes gaseous and thus creates foam. The anaesthetic function of nitrous oxide is not completely understood, but it is thought that the gas interacts with the plasma membranes of nerve cells in the brain and thus affects the communication among such cells at their synapses.

In car racing, nitrous oxide is sometimes injected into the air intake to increase power: even though the gas itself is not flammable, it delivers more oxygen than air and thus allows the engine to burn more fuel.

Nitrous oxide can also be used to produce nitrites by mixing it with boiling alkali metals and to oxidize organic compounds at high temperatures.

The CAS number of nitrous oxide is 10024-97-2 and its UN number is 1070.