Liquid hydrogen - wikipedia Liquid hydrogen Liquid hydrogen Names IUPAC name Liquid hydrogen Other names Hydrogen ( cryogenic liquid ) ; hydrogen, refrigerated liquid ; LH2, para-hydrogen Identifiers CAS Number 1333 - 74 - 0 3D model ( JSmol ) Interactive image ChEBI CHEBI : 33251 ChemSpider 762 KEGG C00282 PubChem CID 783 RTECS number MW8900000 UNII 7YNJ3PO35Z UN number 1966 InChI InChI = 1S / H2 / h1H Key : UFHFLCQGNIYNRP - UHFFFAOYSA - N InChI = 1 / H2 / h1H SMILES ( H ) ( H ) Properties Chemical formula Molar mass 2.02 g mol Appearance Colorless liquid Density 70.85 g / L ( 4.423 lb / cu ft ) Melting point − 259.14 ° C ( 14.01 K ; − 434.45 ° F ) Boiling point − 252.87 ° C ( 20.28 K ; − 423.17 ° F ) Hazards EU classification ( DSD ) ( outdated ) NFPA 704 0 CRYO Autoignition temperature 571 ° C ( 1,060 ° F ; 844 K ) Explosive limits LEL 4.0 % ; UEL 74.2 % ( in air ) Except where otherwise noted, data are given for materials in their standard state ( at 25 ° C ( 77 ° F ), 100 kPa ). Y verify ( what is ? ) Infobox references Liquid hydrogen ( LH2 or LH ) is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H form. To exist as a liquid, H must be cooled below hydrogen 's critical point of 33 K. However, for hydrogen to be in a fully liquid state without boiling at atmospheric pressure, it needs to be cooled to 20.28 K ( − 423.17 ° F / − 252.87 ° C ). One common method of obtaining liquid hydrogen involves a compressor resembling a jet engine in both appearance and principle. Liquid hydrogen is typically used as a concentrated form of hydrogen storage. As in any gas, storing it as liquid takes less space than storing it as a gas at normal temperature and pressure. However, the liquid density is very low compared to other common fuels. Once liquefied, it can be maintained as a liquid in pressurized and thermally insulated containers. There are two spin isomers of hydrogen ; liquid hydrogen consists of 99.79 % parahydrogen and 0.21 % orthohydrogen. Contents 1 History 2 Spin isomers of hydrogen 3 Uses 4 Properties 5 Safety 6 See also 7 References History Further information : Timeline of low - temperature technology In 1885 Zygmunt Florenty Wróblewski published hydrogen 's critical temperature as 33 K ; critical pressure, 13.3 atmospheres ; and boiling point, 23 K. Hydrogen was liquefied by James Dewar in 1898 by using regenerative cooling and his invention, the vacuum flask. The first synthesis of the stable isomer form of liquid hydrogen, parahydrogen, was achieved by Paul Harteck and Karl Friedrich Bonhoeffer in 1929. Spin isomers of hydrogen Main article : Spin isomers of hydrogen The two nuclei in a dihydrogen molecule can have two different spin states. Parahydrogen, in which the two nuclear spins are antiparallel, is more stable than orthohydrogen, in which the two are parallel. At room temperature, gaseous hydrogen is mostly in the ortho isomeric form due to thermal energy, but an ortho - enriched mixture is only metastable when liquified at low temperature. It slowly undergoes an exothermic reaction to become the para isomer, with enough energy released as heat to cause some of the liquid to boil. To prevent loss of the liquid during long - term storage, it is therefore intentionally converted to the para isomer as part of the production process, typically using a catalyst such as iron ( III ) oxide, activated carbon, platinized asbestos, rare earth metals, uranium compounds, chromium ( III ) oxide, or some nickel compounds. Uses Liquid hydrogen is a common liquid rocket fuel for rocketry applications -- both NASA and the United States Air Force operate a large number of liquid hydrogen tanks with an individual capacity up to 3.8 million liters ( 1 million U.S. gallons ). In most rocket engines fueled by liquid hydrogen, it first cools the nozzle and other parts before being mixed with the oxidizer -- usually liquid oxygen ( LOX ) -- and burned to produce water with traces of ozone and hydrogen peroxide. Practical H -- O rocket engines run fuel - rich so that the exhaust contains some unburned hydrogen. This reduces combustion chamber and nozzle erosion. It also reduces the molecular weight of the exhaust, which can actually increase specific impulse, despite the incomplete combustion. Liquid Hydrogen RTECS MW8900000 PEL - OSHA Simple asphyxiant ACGIH TLV - TWA Simple asphyxiant Liquid hydrogen can be used as the fuel for an internal combustion engine or fuel cell. Various submarines ( Type 212 submarine, Type 214 submarine ) and concept hydrogen vehicles have been built using this form of hydrogen ( see DeepC, BMW H2R ). Due to its similarity, builders can sometimes modify and share equipment with systems designed for liquefied natural gas ( LNG ). However, because of the lower volumetric energy, the hydrogen volumes needed for combustion are large. Unless direct injection is used, a severe gas - displacement effect also hampers maximum breathing and increases pumping losses. Liquid hydrogen is also used to cool neutrons to be used in neutron scattering. Since neutrons and hydrogen nuclei have similar masses, kinetic energy exchange per interaction is maximum ( elastic collision ). Finally, superheated liquid hydrogen was used in many bubble chamber experiments. The first thermonuclear bomb, Ivy Mike, used liquid deuterium ( Hydrogen - 2 ), for nuclear fusion. Properties A large hydrogen tank in a vacuum chamber at Lewis Research Center in 1967 The product of its combustion with oxygen alone is water vapor ( although if its combustion is with oxygen and nitrogen it can form toxic chemicals ), which can be cooled with some of the liquid hydrogen. Since water is harmless to the environment, an engine burning it can be considered `` zero emissions. '' Liquid hydrogen also has a much higher specific energy than gasoline, natural gas, or diesel. The density of liquid hydrogen is only 70.99 g / L ( at 20 K ), a relative density of just 0.07. Although the specific energy is more than twice that of other fuels, this gives it a remarkably low volumetric energy density, many fold lower. Liquid hydrogen requires cryogenic storage technology such as special thermally insulated containers and requires special handling common to all cryogenic fuels. This is similar to, but more severe than liquid oxygen. Even with thermally insulated containers it is difficult to keep such a low temperature, and the hydrogen will gradually leak away ( typically at a rate of 1 % per day ). It also shares many of the same safety issues as other forms of hydrogen, as well as being cold enough to liquefy, or even solidify atmospheric oxygen, which can be an explosion hazard. The triple point of hydrogen is at 13.81 K 7.042 kPa. Safety Due to its cold temperatures, liquid hydrogen is a hazard for cold burns. Apart from that, elemental hydrogen as a liquid is biologically inert and its only human health hazard as a vapor is displacement of oxygen, resulting in asphyxiation. Because of its flammability, liquid hydrogen should be kept away from heat or flame unless ignition is intended. See also Tank for liquid hydrogen of Linde, Museum Autovision, Altlußheim, Germany Industrial gas Liquefaction of gases Hydrogen safety Compressed hydrogen Cryo - adsorption Expansion ratio Gasoline gallon equivalent Slush hydrogen Solid hydrogen Metallic hydrogen Hydrogen infrastructure Hydrogen - powered aircraft Liquid hydrogen tank car Liquid hydrogen tanktainer References Jump up ^ Thermophysical Properties of Hydrogen, nist.gov, accessed 2012 - 09 - 14 ^ Jump up to : Information specific to liquid hydrogen Archived 2009 - 07 - 17 at the Wayback Machine., harvard.edu, accessed 2009 - 06 - 12 ^ Jump up to : IPTS - 1968, iupac.org, accessed 2009 - 06 - 12 Jump up ^ Chemical elements data references Jump up ^ Properties Of Gases. Roymech.co.uk. Retrieved on 2011 - 08 - 28. Jump up ^ Liquid Air / LH2. Astronautix.com. Retrieved on 2011 - 08 - 28. ^ Jump up to : `` Liquefaction of `` Permanent '' Gases '' ( PDF of lecture notes ). 2011. Retrieved 2017 - 10 - 16. Jump up ^ Flynn, Thomas ( 2004 ). Cryogenic Engineering, Second Edition, Revised and Expanded. CRC Press. p. 401. ISBN 978 - 0 - 203 - 02699 - 1. ^ Jump up to : Hydrogen As an Alternative Fuel Archived 2008 - 08 - 08 at the Wayback Machine... Almc.army.mil. Retrieved on 2011 - 08 - 28. Jump up ^ Cengel, Yunus A. and Turner, Robert H. ( 2004 ). Fundamentals of thermal - fluid sciences, McGraw - Hill, p. 78, ISBN 0 - 07 - 297675 - 6 Retrieved from `` https://en.wikipedia.org/w/index.php?title=Liquid_hydrogen&oldid=852553860 '' Categories : Hydrogen physics Hydrogen technologies Hydrogen storage Liquid fuels Rocket fuels Coolants Cryogenics Hydrogen Industrial gases 1898 in science Hidden categories : Webarchive template wayback links Chembox having DSD data Articles containing unverified chemical infoboxes Talk Contents About Wikipedia تۆرکجه Беларуская Беларуская ( тарашкевіца ) ‎ Català Deutsch Ελληνικά Español فارسی Français 한국어 Bahasa Indonesia Bahasa Melayu Nederlands 日本 語 Português Română Русский Српски / srpski Srpskohrvatski / српскохрватски Suomi தமிழ் ไทย Türkçe Українська Tiếng Việt 中文 18 more Edit links This page was last edited on 29 July 2018, at 19 : 59 ( UTC ). Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. 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Question: at what temperature does hydrogen become a liquid
Answer: 20.28 K[3] (−423.17 °F/−252.87 °C)