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Nitrous oxide

Structure of Nitrous oxide


Name Dinitrogen oxide
Chemical formula N2O
Appearance Colorless gas


Formula weight 44.0 u
Melting point 182 K (-91 °C)
Boiling point 185 K (-88 °C)
Critical temperature 309.6 K (36.4 °C)
Critical pressure 7.245 MPa
Density 1.2 g/cm3 (liquid)
Solubility 0.112 g in 100g water


ΔfH0gas 82.05 kJ/mol
ΔfH0liquid ? kJ/mol
ΔfH0solid ? kJ/mol
S0gas, 100 kPa 219.96 J/(mol·K)
S0liquid, 100 kPa ? 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 due to the exhilarating effects of inhaling it. It is used in surgery and dentistry for its anaesthetic and analgesic effects. Nitrous oxide is present in the atmosphere where it acts as a powerful greenhouse gas.



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 can be considered a resonance hybrid of

\mbox{N} \equiv \mbox{N}^+ - \mbox{O}^-    and    \mbox{N}^-= \mbox{N}^+= \mbox{O}\;

Nitrous oxide N2O should not be confused with the other nitrogen oxides such as nitric oxide NO and nitrogen dioxide NO2.

Nitrous oxide can 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.


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, who do not typically have access to the services of an anesthesologist and who may benefit from a patient who can respond to verbal commands.


Inhalant effects — laughing gas

Nitrous oxide is a dissociative which causes (by some accounts) euphoria, dizziness, and, in some cases, a mild aphrodisiac effect. It can also result in mild nausea or lingering dizziness if too much is inhaled in too short a time. 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.

Some people use nitrous oxide for its psychological effects. 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. Long-term use in large quantities has been associated with symptoms similar to vitamin B12 deficiency: anemia and neuropathy. It can be habit-forming, mainly because of its short-lived effect and ease of access. Its use is thus restricted in many districts. In California, for instance, inhalation of nitrous oxide "for the purpose of causing euphoria, or for the purpose of changing in any manner, one’s mental processes," is a criminal offense. (See, Cal. Pen. Code, Sec. 381b.) The Centre for Cognitive Liberty and Ethics, a nonprofit law and policy center in the United States, contends that such laws are unconstitional "prior restraints on speech" and constitute "cognitive censorship."

A 50/50 mixture of nitrous oxide and oxygen ("gas and air", supplied under the trade name Entonox) is commonly used as a mild analgesic and anaesthetic in medicine, paticularly during childbirth, for dental procedures, and in emergency medicine.

Aerosol propellant

The gas is licensed for use as a food additive, specifically as an aerosol propellant . Its most common uses in this context are in aerosol whipped cream canisters and as an inert gas used to displace staleness-inducing oxygen when filling packages of potato chips and other similar snack foods.

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.

Rocket motors

Nitrous oxide can be used as an oxidiser in a rocket engine. This has the advantages over other oxidisers that it is non-toxic and, due to its stability at room temperature, easy to store and relatively safe to carry on a flight.

Nitrous oxide has notably been the oxidiser of choice in several hybrid rocket designs (using solid fuel with a liquid or gaseous oxidiser). The combination of nitrous oxide with hydroxy-terminated polybutadiene fuel has been used by SpaceShipOne and others.

Internal Combustion Engine

In car racing, nitrous oxide (often just "nitrous" or "nitro" in this context) is sometimes injected into the intake manifold (or just prior to the intake manifold) to increase power: even though the gas itself is not flammable, it delivers more oxygen than atmospheric air by breaking down at elevated temperatures, thus allowing the engine to burn more fuel and air. Additionally, since nitrous oxide is stored as a liquid, the evaporation of liquid nitrous oxide in the intake manifold causes a large drop in intake charge temperature. This results in a smaller, denser charge, and can reduce detonation, as well as increase power available to the engine.

The same technique was used during World War II to boost the power of aircraft engines, particularly by the Luftwaffe which had less access to fuel with higher octane ratings than did the Royal Air Force and United States Air Force.

It is very important with nitrous oxide augmentation of internal combustion engines to maintain temperatures and fuel levels so as to prevent preignition, or detonation (sometimes referred to as knocking, pinging or pinking).

Nitrous oxide in the atmosphere

Nitrogen oxides, nitrous oxide included, are greenhouse gasses; nitrous oxide has 270 times the effect of carbon dioxide for producing global warming. Therefore, nitrogen oxides are a subject of efforts to curb greenhouse gas emissions, such as the Kyoto Protocol.

Nitrous oxide is naturally emitted from soils and oceans. Human activity contributes to the release of the gas through the cultivation of soil and the use of nitrogen fertilizers , the production of nylon, and the burning of fossil fuels and other organic matter.

Laughing Gas in fiction

External links

Last updated: 06-02-2005 03:09:58
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