Hydrogen

The least dense element. It has metallic and non-metallic properties. The most abundant element in the universe. Hydrogen occurs as H2 at ambient temperature and pressure, a colourless, odourless, and extremely flammable gas. In its free gaseous state it is only found in nature in small quantities issuing from crevices in volcanic areas or near petroleum wells. It exists in combination everywhere; as a constituent of water, of all plants and animals, and in numerous minerals, abundantly in coal, petroleum, bitumen, etc., and to a lesser degree in rocks. The element may be separated from any of its compounds, but it is usually obtained from water or dilute acids.

Hydrogen is not a source of energy. It is only a way of storing and transporting it. Although hydrogen is the most abundant element in the Universe (and in the more immediate neighbourhood, it makes up 90 percent of the atoms in the Sun and Jupiter), there is virtually no hydrogen gas on Earth. Our gravity is so weak that essentially all our primordial hydrogen—except that which bound itself into heavier compounds—escaped into space billions of years ago.

Hydrogen fuel must be “manufactured” by extracting it from water and methane. You get out from hydrogen fuel only the energy you put into extraction, or from burning carbon in the process.

Water can be split into hydrogen and oxygen by electric current, the process known as electrolysis. Plain heat will do the trick too. Above 2700°C water spontaneously decomposes. On a sufficiently hot fire, water decomposes and then recombines when it cools.

Splitting water is expensive, and the oxygen is not required. A much cheaper way to produce hydrogen is to spray steam on white-hot coals. This results in mostly hydrogen gas (40 percent) and carbon monoxide (50 percent), a mixture known appropriately as “water gas.” It’s the least expensive way to make hydrogen. Unfortunately, the carbon monoxide produced along with it is highly poisonous. To extract the last bit of energy, the carbon monoxide can be burned, and that turns it into the greenhouse gas carbon dioxide.

The production of water gas began in earnest in the 1870s. The other common “manufactured” gas back then was coal gas, extracted from bituminous coal by heating it in an oxygen-free environment. Coal gas went to streetlamps and homes, and the more dangerous water gas was used by industry. Water gas is still used extensively in steel manufacture and in the so-called Fisher-Tropsch process, which is used to make synthetic gasoline and alcohols.

In the 1920s, the discovery of large underground reserves of methane provided a cheaper alternative to coal gas. Since it wasn’t manufactured, it was called “natural gas,” the name still used today. Methane also replaced coal for water gas production. As with coal, producing hydrogen from methane yields abundant carbon monoxide that upon combustion becomes carbon dioxide.


Symbol
H

Also known as
Inflammable Air, Phlogiston Elasticum

Discovered
1766 by Henry Cavendish.

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Atomic number 1 Clip
Atomic / Molecular Weight 1.00794 gmol-1Clip
Density 0.08987 kgm-3Clip
Lattice constant 378 fmClip
Melting Point 13.96 KClip
Boiling Point 20.29 KClip
Autoignition Temperature 809 KClip
Specific heat capacity 14300 Jkg-1K-1Clip
Latent heat of evaporation 453000 Jkg-1Clip
Ratio of Specific Heats 1.404 Clip
Thermal conductivity 0.1684 Wm-1K-1Clip
Refractive index 1.000132 at 589.3nm 101.3kPa 0°CClip
Refractivity 0.000132 Clip
Acoustic wave velocity (Irrotational waves) 1284 ms-1Clip
Viscosity 0.00000835 Nsm-2Clip
Kinematic Viscosity 9.29119839768554E-05 m2s-1Clip
Critical Temperature 33.3 KClip
Critical Pressure 12940000 PaClip
Critical Volume 0.0000655 m3mol-1Clip
de Broglie wavelength 0.000000000114 mClip
Electromotive Series 0 VClip
Triple Point Equilibrium 13.81 Normal 13.956 KClip
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See also: Brackett Series, Cavendish, Henry, Compressed Hydrogen Gas, Deuterium, Heavy Water, Hydrocarbon, Hydrogen Bonding, Hydrogen Burning, Hydrogen Economy, Hydrogen Embrittlement, Hydrogen Storage, Hydrogenation, Hydrophilic, Liquefied Hydrogen, Liquid Organic Hydrogen Carriers, Lyman Series, Organic Compound, Paschen Series, Periodic Table, Pfund Series, Protium, Reformer, Reforming, Slush Hydrogen, Steam Reforming, Tautomer, Tritium, Water.

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Subjects: Chemistry


Weblinks:
National Hydrogen Association of Australia Exists to promote the renewable energy source of hydrogen throughout Australia.
Hydrogen.com Information and resource center.
Sun Catalytix Commercializing new, active, versatile, and affordable catalysts that split water into oxygen and hydrogen fuel, mimicking photosynthesis.