 Discovery Information
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| Who: Henry Cavendish |
| When: 1766 |
| Where: England |
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| Name Origin
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| Greek: hudor (water) and gennan (generate) |
| "Hydrogen" in different languages. |
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| Sources
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| Found chiefly combined with oxygen in the form of water, also found in mines and oil and gas wells. Stars contain a virtually unlimited supply of hydrogen and
in the universe, hydrogen is the most abundant element (hydrogen makes up 75% of the mass of the visible universe and over
90% by number of atoms.).
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| Annual world production of hydrogen is around 350 billion cubic metres. |
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| Abundance
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| Universe: 7.5 x 105 ppm (by weight)
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| Sun: 7.5 x 105 ppm (by weight)
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| Carbonaceous meteorite: 24000 ppm |
| Earth's Crust: 1500 ppm |
| Seawater: 107800 ppm |
| Human: |
| 1 x 108 ppb by weight
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| 6.2 x 108 ppb by atoms
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| Uses
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| Hydrogen's uses include: being used in the production of ammonia (NH3), ethanol (C2H5OH), hydrogen chloride (HCl) and hydrogen bromide (HBr); the hydrogenation of vegetable oils; hydrocracking, hydroforming and hydrofining of petroleum; atomic-hydrogen welding;
instrument-carrying balloons; fuel in rockets; and cryogenic research. Its two heavier isotopes, deuterium (D) and tritium (T), are used respectively for nuclear fission and fusion.
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| Hydrogen fuel cells are being investigated as mobile power sources with lower emissions than hydrogen-burning internal combustion
engines. The low emissions of hydrogen in internal combustion engines and fuel cells are currently offset by the pollution
created by hydrogen production. This may change if the substantial amounts of electricity required for water electrolysis
can be generated primarily from low pollution sources such as solar energy or wind. Research is being conducted on H2 as a replacement for fossil fuels.
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| History
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| Hydrogen gas, H2, was first artificially produced and formally described by T. Von Hohenheim (also known as Paracelsus, 1493 - 1541) via the
mixing of metals with strong acids. He was unaware that the flammable gas produced by this chemical reaction was a new chemical
element. In 1671, Robert Boyle rediscovered and described the reaction between iron filings and dilute acids, which results in the production of hydrogen gas. In 1766, Henry Cavendish was the first to recognize hydrogen gas as a discrete substance, by identifying the gas from a metal-acid reaction as "inflammable
air" and further finding that the gas produces water when burned. Cavendish had stumbled on hydrogen when experimenting with acids and mercury. Although he wrongly assumed that hydrogen was a liberated component of the mercury rather than the acid, he was still able
to accurately describe several key properties of hydrogen. He is usually given credit for its discovery as an element. In
1783, Antoine Lavoisier gave the element the name of hydrogen when he (with Laplace) reproduced Cavendish's finding that water is produced when hydrogen is burned. Lavoisier's name for the gas won out.
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| One of the first uses of H2 was for balloons, and later airships. The H2 was obtained by reacting sulphuric acid and metallic iron. Infamously, H2 was used in the Hindenburg airship that was destroyed in a midair fire. The highly flammable hydrogen (H2) was later replaced for airships and most balloons by the unreactive helium (He).
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| Notes
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| At standard temperature and pressure, hydrogen exists as the diatomic gas, H2, with a boiling point of 20.27 K, and a melting point of 14.02 K. Under extreme pressures, such as those at the center of gas giants, the molecules lose their identity and the hydrogen becomes a metal (metallic hydrogen). Under the extremely low pressure in space - virtually
a vacuum - the element tends to exist as individual atoms, simply because it is statistically unlikely for them to combine.
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| A unique property of hydrogen is that its flame is nearly invisible in air.
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| Hazards
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| Hydrogen is a tasteless, colourless, odourless and extremely flammable gas, it is also the lightest chemical element. |
