Liquid hydrogen

Liquid hydrogen (H2(l)) is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form.

Liquid hydrogen
Names
IUPAC name
Hydrogen
Systematic IUPAC name
Liquid hydrogen
Other names
Hydrogen (cryogenic liquid), Refrigerated hydrogen; LH2, para-hydrogen
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
KEGG
RTECS number
  • MW8900000
UNII
UN number 1966
  • InChI=1S/H2/h1H Y
    Key: UFHFLCQGNIYNRP-UHFFFAOYSA-N Y
  • InChI=1/H2/h1H
  • [H][H]
Properties
H2(l)
Molar mass 2.016 g·mol−1
Appearance Colorless liquid
Density 0.07085 g/cm3 (4.423 lb/cu ft)
Melting point −259.14 °C (−434.45 °F; 14.01 K)
Boiling point −252.87 °C (−423.17 °F; 20.28 K)
Hazards
GHS labelling:
Danger
H220, H280
P210, P377, P381, P403
NFPA 704 (fire diamond)
3
4
0
CRYO
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 YN ?)
Infobox references

To exist as a liquid, H2 must be cooled below its critical point of 33 K. However, for it to be in a fully liquid state at atmospheric pressure, H2 needs to be cooled to 20.28 K (−252.87 °C; −423.17 °F). A 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. 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 for some time in thermally insulated containers.

There are two spin isomers of hydrogen; whereas room temperature hydrogen is mostly orthohydrogen, liquid hydrogen consists of 99.79% parahydrogen and 0.21% orthohydrogen.

Hydrogen requires a theoretical minimum of 3.3 kWh/kg to liquefy, and 3.9 kWh/kg including converting the hydrogen to the para isomer, but practically generally takes 10–13 kWh/kg compared to a 33 kWh/kg heating value of hydrogen.

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