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| Hydrogen was
isolated and identified in 1766 by Henry Cavendish, and it was he
who conclusively established that water is a compound of hydrogen
and oxygen, although the name hydrogen (Greek for water former) is
credited to Lavoisier in 1783. Hydrogen is the lightest element, colourless, tasteless, odourless and flammable. It is present in water and in all organic compounds. It burns in oxygen or air with a near colourless flame and since its products of combustion are water plus nitrogen, if burnt in air, it has great potential to reduce atmospheric pollution, compared to hydrocarbon based fuels. In gaseous form its low weight gives is a density one-fourteen of air whilst in crystalline form it’s the lightest of all crystalline substances (lighter then marshmallow). Hydrogen is thought to be the most abundant element in the universe and is the third most abundant on earth after oxygen and silicon. Its abundance can be seen by noting it has been estimated that every cubic centimetre of dark interstellar space, essentially void of any other known matter, contains a few atoms of hydrogen (ref Steven Weinberg: The first three minutes). Although it has a simple electron configuration, one proton/electron and no neutrons, it can exist in over 40 different forms due to; the existence of atomic, molecular and ionised species in the gas phase, its three isotopes and its nuclear spin isotopes. Terrestrial hydrogen also contains a very small amount, ~ 0.0156%, of deuterium atoms and this does cause variability in its atomic weight. The three isotopes are; hydrogen, heavy hydrogen (deuterium) and tritium, which is radioactive and made artificially. The gas is diatomic and can exist with two nuclear spins, parallel (ortho-hydrogen) and antiparallel (para-hydrogen). At 0 K hydrogen is 100% para but as the temperature increases the ortho content increases until at room temperature the mix is 75% ortho and 25% para. |
Liquid hydrogen is 99.8%
parahydrogen.Hydrogen can be prepared using a number of different
processes including; hydrolysis of metal hydrides, electrolysis of
water and the reaction of steam with hydrocarbons or coke. The first
of these is convenient for small sale production, the second for the
production of high purity gases and the third is the most common method
as used for large scale production. Electrolysis is also used in the
chlor-alkali industry where hydrogen is a by-product but it lacks
the purity of hydrogen derived by simple electrolysis of water. Hydrogen does not obey the perfect gas laws making property prediction more complex. |
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