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  2. Hydrogen - Wikipedia

    en.wikipedia.org/wiki/Hydrogen

    It is the lightest element and, at standard conditions, is a gas of diatomic molecules with the formula H 2, sometimes called dihydrogen, [11] hydrogen gas, molecular hydrogen, or simply hydrogen. It is colorless, odorless, [ 12 ] non-toxic, and highly combustible .

  3. Liquid hydrogen - Wikipedia

    en.wikipedia.org/wiki/Liquid_hydrogen

    Liquid hydrogen (H 2 (l)) is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H 2 form. [4] To exist as a liquid, H 2 must be cooled below its critical point of 33 K. However, for it to be in a fully liquid state at atmospheric pressure, H 2 needs to be cooled to 20.28 K (−252.87 °C; −423.17 °F). [5]

  4. Hydrogen cycle - Wikipedia

    en.wikipedia.org/wiki/Hydrogen_cycle

    The hydrogen cycle consists of hydrogen exchanges between biotic (living) and abiotic (non-living) sources and sinks of hydrogen-containing compounds. Hydrogen (H) is the most abundant element in the universe. [1] On Earth, common H-containing inorganic molecules include water (H 2 O), hydrogen gas (H 2), hydrogen sulfide (H 2 S), and ammonia ...

  5. Hydrogen production - Wikipedia

    en.wikipedia.org/wiki/Hydrogen_production

    High pressure electrolysis is the electrolysis of water by decomposition of water (H 2 O) into oxygen (O 2) and hydrogen gas (H 2) by means of an electric current being passed through the water. The difference with a standard electrolyzer is the compressed hydrogen output around 120–200 bar (1740–2900 psi , 12–20 MPa ). [ 146 ]

  6. State of matter - Wikipedia

    en.wikipedia.org/wiki/State_of_matter

    A gas is usually converted to a plasma in one of two ways, either from a huge voltage difference between two points, or by exposing it to extremely high temperatures. Heating matter to high temperatures causes electrons to leave the atoms, resulting in the presence of free electrons. This creates a so-called partially ionised plasma.

  7. Hydrogen chloride - Wikipedia

    en.wikipedia.org/wiki/Hydrogen_chloride

    The compound hydrogen chloride has the chemical formula HCl and as such is a hydrogen halide.At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor.

  8. H II region - Wikipedia

    en.wikipedia.org/wiki/H_II_region

    NGC 604, a giant H II region in the Triangulum Galaxy, taken by the Hubble Space Telescope. An H II region is a region of interstellar atomic hydrogen that is ionized. [1] It is typically in a molecular cloud of partially ionized gas in which star formation has recently taken place, with a size ranging from one to hundreds of light years, and density from a few to about a million particles per ...

  9. Heat of combustion - Wikipedia

    en.wikipedia.org/wiki/Heat_of_combustion

    For a fuel of composition C c H h O o N n, the (higher) heat of combustion is 419 kJ/mol × (c + 0.3 h − 0.5 o) usually to a good approximation (±3%), [2] [3] though it gives poor results for some compounds such as (gaseous) formaldehyde and carbon monoxide, and can be significantly off if o + n > c, such as for glycerine dinitrate, C 3 H 6 ...