When nitrogen is liquefied, heat is released

Nitrogen, N2, is at standard conditions a colorless odorless gas. The gas makes up the major portion of the atmosphere, but will not support life by itself. Refrigerated (cryogenic) nitrogen, is a colorless odorless liquid.

Gaseous nitrogen is used in food processing, in purging air conditioning and refrigeration systems, and in pressurizing aircraft tires. Liquid nitrogen is used to freeze foods, to preserve whole blood and other biologicals, and as a coolant.

Nitrogen is nontoxic and noncombustible, but it may cause asphyxiation by displacement of air. Liquid nitrogen is very cold and and contact may cause frostbite. Under prolonged exposure to fire or heat, nitrogen containers may rupture violently and rocket.

The phase diagram of nitrogen is shown below the table.

Chemical, physical and thermal properties of Nitrogen:
Values at 25oC (77oF, 298 K) and atmospheric pressure

Molecular Weight28.013Specific Gravity, air = 10.967Specific Volume (ft3/lb, m3/kg)13.98, 0.872Density of liquid at atmospheric pressure (lb/ft3, kg/m3)50.46, 808.4Absolute Viscosity (lbm/ft s, centipoises)12.1 10-6, 0.018Sound velocity in gas (m/s)353Specific Heat - cp - (Btu/lboF or cal/goC, J/kgK)0.249, 1040Specific Heat Ratio - cp/cv1.40Gas constant - R - (ft lb/lboR, J/kgoC)55.2, 297Thermal Conductivity (Btu/hr ft oF, W/moC)0.015, 0.026Boiling Point - at saturation pressure 14.7 psia and 760 mm Hg - (oF, oC)-320.4, -195.8Latent Heat of Evaporation at boiling point (Btu/lb, J/kg)85.5, 199000Freezing or Melting Point  at 1 atm (oF, oC)-346, -210Latent Heat of Fusion (Btu/lb, J/kg)11.1, 25800Critical Temperature (oF, oC)-232.6, -147Critical Pressure (psia, MN/m2)493, 3.40Critical Volume (ft3/lb, m3/kg)0.051, 0.00318Flammableno

Follow the links below to get values for the listed properties of nitrogen at varying pressure and temperature:

See also more about atmospheric pressure, and STP - Standard Temperature and Pressure & NTP - Normal Temperature and Pressure,
as well as Thermophysical properties of: Acetone, Acetylene, Air, Ammonia, Argon, Benzene, Butane, Carbon dioxide, Carbon monoxide, Ethane, Ethanol, Ethylene, Helium, Hydrogen, Hydrogen sulfide, Methane, Methanol, Oxygen, Pentane, Propane, Toluene, Water and Heavy water, D2O.

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Nitrogen is a gas at standard conditions. However, at low temperature and/or high pressures the gas becomes a liquid or a solid.

The nitrogen phase diagram shows the phase behavior with changes in temperature and pressure. The curve between the critical point and the triple point shows the nitrogen boiling point with changes in pressure. It also shows the saturation pressure with changes in temperature.

At the critical point there is no change of state when pressure is increased or if heat is added.

The triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium.

A demonstration of liquid nitrogen at the Freeside maker space in Atlanta, Georgia during the Online News Association conference in 2013

Liquid nitrogen—LN2—is nitrogen in a liquid state at low temperature. Liquid nitrogen has a boiling point of about −195.8 °C (−320 °F; 77 K). It is produced industrially by fractional distillation of liquid air. It is a colorless, low viscosity liquid that is widely used as a coolant.

Physical properties[edit]

The diatomic character of the N2 molecule is retained after liquefaction. The weak van der Waals interaction between the N2 molecules results in little interatomic interaction, manifested in its very low boiling point.[1]

The temperature of liquid nitrogen can readily be reduced to its freezing point −210 °C (−346 °F; 63 K) by placing it in a vacuum chamber pumped by a vacuum pump.[2] Liquid nitrogen's efficiency as a coolant is limited by the fact that it boils immediately on contact with a warmer object, enveloping the object in an insulating layer of nitrogen gas bubbles. This effect, known as the Leidenfrost effect, occurs when any liquid comes in contact with a surface which is significantly hotter than its boiling point. Faster cooling may be obtained by plunging an object into a slush of liquid and solid nitrogen rather than liquid nitrogen alone.[2]

Handling[edit]

As a cryogenic fluid that rapidly freezes living tissue, its handling and storage require thermal insulation. It can be stored and transported in vacuum flasks, the temperature being held constant at 77 K by slow boiling of the liquid. Depending on the size and design, the holding time of vacuum flasks ranges from a few hours to a few weeks. The development of pressurised super-insulated vacuum vessels has enabled liquid nitrogen to be stored and transported over longer time periods with losses reduced to 2% per day or less.[3]

Liquid nitrogen is a compact and readily transported source of dry nitrogen gas, as it does not require pressurization. Further, its ability to maintain temperatures far below the freezing point of water makes it extremely useful in a wide range of applications, primarily as an open-cycle refrigerant, including:

Culinary[edit]

The culinary use of liquid nitrogen is mentioned in an 1890 recipe book titled Fancy Ices authored by Mrs. Agnes Marshall,[12] but has been employed in more recent times by restaurants in the preparation of frozen desserts, such as ice cream, which can be created within moments at the table because of the speed at which it cools food.[12] The rapidity of chilling also leads to the formation of smaller ice crystals, which provides the dessert with a smoother texture.[12] The technique is employed by chef Heston Blumenthal who has used it at his restaurant, The Fat Duck, to create frozen dishes such as egg and bacon ice cream.[12][13] Liquid nitrogen has also become popular in the preparation of cocktails because it can be used to quickly chill glasses or freeze ingredients.[14] It is also added to drinks to create a smoky effect, which occurs as tiny droplets of the liquid nitrogen come into contact with the surrounding air, condensing the vapour that is naturally present.[14]

Nitrogen was first liquefied at the Jagiellonian University on 15 April 1883 by Polish physicists Zygmunt Wróblewski and Karol Olszewski.[15]

Filling a liquid nitrogen Dewar from a storage tank

Because the liquid-to-gas expansion ratio of nitrogen is 1:694 at 20 °C (68 °F), a tremendous amount of force can be generated if liquid nitrogen is vaporized in an enclosed space. In an incident on January 12, 2006 at Texas A&M University, the pressure-relief devices of a tank of liquid nitrogen were malfunctioning and later sealed. As a result of the subsequent pressure buildup, the tank failed catastrophically. The force of the explosion was sufficient to propel the tank through the ceiling immediately above it, shatter a reinforced concrete beam immediately below it, and blow the walls of the laboratory 0.1–0.2 m off their foundations.[16]

Because of its extremely low temperature, careless handling of liquid nitrogen and any objects cooled by it may result in cold burns. In that case, special gloves should be used while handling. However, a small splash or even pouring down skin will not burn immediately because of the Leidenfrost effect, the evaporating gas thermally insulates to some extent, like touching a hot element very briefly with a wet finger. If the liquid nitrogen manages to pool anywhere, it will burn severely.

As liquid nitrogen evaporates it reduces the oxygen concentration in the air and can act as an asphyxiant, especially in confined spaces. Nitrogen is odorless, colorless, and tasteless and may produce asphyxia without any sensation or prior warning.[17][18][19]

Oxygen sensors are sometimes used as a safety precaution when working with liquid nitrogen to alert workers of gas spills into a confined space.[20]

Vessels containing liquid nitrogen can condense oxygen from air. The liquid in such a vessel becomes increasingly enriched in oxygen (boiling point 90 K; −183 °C; −298 °F) as the nitrogen evaporates, and can cause violent oxidation of organic material.[21]

Ingestion of liquid nitrogen can cause severe internal damage, due to freezing of the tissues which come in contact with it and to the volume of gaseous nitrogen evolved as the liquid is warmed by body heat. In 1997, a physics student demonstrating the Leidenfrost effect by holding liquid nitrogen in his mouth accidentally swallowed the substance, resulting in near-fatal injuries. This was apparently the first case in medical literature of liquid nitrogen ingestion.[22] In 2012, a young woman in England had her stomach removed after ingesting a cocktail made with liquid nitrogen.[23] In January 2021, a line carrying liquid nitrogen ruptured at a poultry processing plant in the U.S. state of Georgia, killing six people and injuring 11 others.

Production[edit]

Liquid nitrogen is produced commercially from the cryogenic distillation of liquified air or from the liquefication of pure nitrogen derived from air using pressure swing adsorption. An air compressor is used to compress filtered air to high pressure; the high-pressure gas is cooled back to ambient temperature, and allowed to expand to a low pressure. The expanding air cools greatly (the Joule–Thomson effect), and oxygen, nitrogen, and argon are separated by further stages of expansion and distillation. Small-scale production of liquid nitrogen is easily achieved using this principle.[citation needed] Liquid nitrogen may be produced for direct sale, or as a byproduct of manufacture of liquid oxygen used for industrial processes such as steelmaking. Liquid-air plants producing on the order of tons per day of product started to be built in the 1930s but became very common after the Second World War; a large modern plant may produce 3000 tons/day of liquid air products.[25]

What happens when nitrogen is liquefied?

What happens when liquid nitrogen is heated?

Does liquid nitrogen have heat energy?

Is liquid nitrogen endothermic or exothermic?