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(Gr. hydro, water, and genes, forming) Hydrogen was prepared many years before it was
recognized as a distinct substance by Cavendish in 1776.
Named by Lavoisier, hydrogen is the most abundant of all elements in the universe. The
heavier elements were originally made from Hydrogen or from other elements that were
originally made from Hydrogen.
Hydrogen is estimated to make up more than 90% of all the atoms or three quarters of
the mass of the universe. This element is found in the stars, and plays an important part
in powering the universe through both the proton-proton reaction and carbon-nitrogen cycle
-- stellar hydrogen fusion processes that release massive amounts of energy by combining
Hydrogen to form Helium.
Production of hydrogen in the U.S. alone now amounts to about 3 billion cubic feet per
year. Hydrogen is prepared by
- steam on heated carbon,
- decomposition of certain hydrocarbons with heat,
- action of sodium or potassium hydroxide on aluminum
- electrolysis of water, or
- displacement from acids by certain metals.
Liquid hydrogen is important in cryogenics and in the study of superconductivity, as
its melting point is only 20 degrees above absolute zero.
Tritium is readily produced in nuclear reactors and is used in the production of the
Hydrogen is the primary component of Jupiter and the other gas giant planets.
At some depth in the planet's interior the pressure is so great that solid
molecular hydrogen is converted to solid metallic hydrogen.
In 1973, a group of Russian experimenters may have produced metallic hydrogen at a
pressure of 2.8 Mbar. At the transition the density changed from 1.08 to 1.3 g/cm3. Earlier, in 1972, at
Livermore, California, a group also reported on a similar experiment in which they
observed a pressure-volume point centered at 2 Mbar. Predictions say that metallic
hydrogen may be metastable; others have predicted it would be a superconductor at room
Although pure Hydrogen is a gas we find very little of it in our atmosphere.
Hydrogen gas is so light that uncombined Hydrogen will gain enough velocity from
collisions with other gases that they will quickly be ejected from the atmosphere.
On earth, hydrogen occurs chiefly in combination with oxygen in water, but it is
also present in organic matter such as living plants, petroleum, coal, etc. It is present
as the free element in the atmosphere, but only to the extent of less than 1 ppm by
volume. The lightest of all gases, hydrogen combines with other elements -- sometimes
explosively -- to form compounds.
Great quantities are required commercially for the fixation of nitrogen from the air in
the Haber ammonia process and for the hydrogenation of fats and oils. It is also used in
large quantities in methanol production, in hydrodealkylation, hydrocracking, and
hydrodesulfurization. Other uses include rocket fuel, welding, producing hydrochloric
acid, reducing metallic ores, and filling balloons.
The lifting power of 1 cubic foot of hydrogen gas is about 0.07 lb at 0C, 760 mm
The Hydrogen Fuel cell is a developing technology that will allow great amounts of
electrical power to be obtained using a source of hyrogen gas.
Consideration is being given to an entire economy based on solar- and nuclear-generated
hydrogen. Public acceptance, high capital investment, and the high cost of hydrogen with
respect to today's fuels are but a few of the problems facing such an economy.
Located in remote regions, power plants would electrolyze seawater; the hydrogen
produced would travel to distant cities by pipelines. Pollution-free hydrogen could
replace natural gas, gasoline, etc., and could serve as a reducing agent in metallurgy,
chemical processing, refining, etc. It could also be used to convert trash into methane
Quite apart from isotopes, it has been shown that under ordinary conditions hydrogen
gas is a mixture of two kinds of molecules, known as ortho- and para-hydrogen, which
differ from one another by the spins of their electrons and nuclei.
Normal hydrogen at room temperature contains 25% of the para form and 75% of the ortho
form. The ortho form cannot be prepared in the pure state. Since the two forms differ in
energy, the physical properties also differ. The melting and boiling points of
parahydrogen are about 0.1oC
lower than those of normal hydrogen.
The ordinary isotope of hydrogen, H, is known as Protium, the other two isotopes are
Deuterium (a proton and a neutron) and Tritium (a protron and two neutrons). Hydrogen is
the only element whose isotopes have been given different names. Deuterium and Tritium are
both used as fuel in nuclear fusion reactors. One atom of Deuterium is found in about 6000
ordinary hydrogen atoms.
Deuterium is used as a moderator to slow down neutrons. Tritium atoms are also present
but in much smaller proportions. Tritium is readily produced in nuclear reactors and is
used in the production of the hydrogen (fusion) bomb. It is also used as a radioactive
agent in making luminous paints, and as a tracer.
Sources: CRC Handbook of Chemistry
and Physics and the American Chemical Society.