| Hydrogen was prepared many years before it was recognized as a distinct
substance by Cavendish in 1766. It was named by Lavoisier. Hydrogen is the most abundant of all elements in the universe, and it is thought that the
heavier elements were, and still are, being built from hydrogen and helium. It has been estimated that hydrogen makes up more than 90% of all the
atoms or three quarters of the mass of the universe. It is found in the sun and most stars, and plays an important part in the proton-proton reaction and
carbon-nitrogen cycle, which accounts for the energy of the sun and stars. It is thought that hydrogen is a major component of the planet Jupiter and
that at some depth in the planet’s interior the pressure is so great that solid molecular hydrogen is converted into solid metallic hydrogen. In 1973, it
was reported that 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, a Livermore (California) group also reported on a similar experiment in which they observed a
pressure-volume point centered at 2 Mbar. It has been predicted that metallic hydrogen may be metastable; others have predicted it would be a
superconductor at room temperature. 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. It
is the lightest of all gases, and combines with other elements, sometimes explosively, to form compounds. Great quantities of hydrogen 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. It is also used as a rocket fuel, for welding, for
production of hydrochloric acid, for the reduction of metallic ores, and for filling balloons. The lifting power of 1 ft3 of hydrogen gas is about 0.076
lb at 0°C, 760 mm pressure. Production of hydrogen in the U.S. alone now amounts to about 3 billion cubic feet per year. It is prepared by the action
of steam on heated carbon, by decomposition of certain hydrocarbons with heat, by the electrolysis of water, or by the displacement from acids by certain
metals. It is also produced by the action of sodium or potassium hydroxide on aluminum. Liquid hydrogen is important in cryogenics and in the study
of superconductivity, as its melting point is only a 20 degrees above absolute zero. The ordinary isotope of hydrogen, H, is known as protium. In 1932,
Urey announced the discovery of a stable isotope, deuterium (2H or D) with an atomic weight of 2. Deuterium is present in natural hydrogen to the
extent of 0.015%. Two years later an unstable isotope, tritium (H), with an atomic weight of 3 was discovered. Tritium has a half-life of about 12.5
years. Tritium atoms are also present in hydrogen but in much smaller proportion. Tritium is readily produced in nuclear reactors and is used in the
production of the hydrogen bomb. It is also used as a radioactive agent in making luminous paints, and as a tracer. Deuterium gas is readily available,
without permit, at about $1/L. Heavy water, deuterium oxide (D2O), which is used as a moderator to slow down neutrons, is available without permit
at a cost of 6c to $1/g, depending on quantity and purity. Quite apart from isotopes, it has been shown that hydrogen gas under ordinary conditions
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 0.1°C lower than
those of normal hydrogen. Consideration is being given to an entire economy based on solar- and nuclear-generated hydrogen. Located in remote
regions, power plants would electrolyze sea water; 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 and ethylene. Public acceptance, high capital investment, and the high present cost of hydrogen with respect to present fuels are
but a few of the problems facing establishment of such an economy. 1 |
| At room temperature, B2Cl4 will react quickly with hydrogen producing diborane, B2H6 and boron trichloride. |
| Hydrides such as diborane (B2H6) react with water to produce hydrogen gas and boric acid. |
| Lithium hydride is a very reactive compound. Upon reaction with titanium (IV) chloride, elemental titanium and hydrogen are produced. Lithium chloride is also a product of the reaction. |
| Ores of iron are often a mixture of oxides represented by the formula Fe3O4. At elevated temperatures the reaction of this oxide with hydrogen gas yields iron metal and water vapor. |
| Methyl alcohol, CH3OH, is a clean-burning, easily handled fuel. It can be made by the direct reaction of carbon monoxide and hydrogen (obtained from coal and water). |
| Potassium metal reacts with water to produce aqueous potassium hydroxide and hydrogen gas. |
| The principal method used to prepare hydrogen industrially starts with natural gas. The major component of natural gas is methane, CH4. When this is heated with steam, a reaction occurs which yields hydrogen gas and a carbon monoxide byproduct. |
| Very pure hydrogen can be prepared from the electrolysis of water. A small amount of an ionic compounds like sodium hydroxide is added to the water to provide the ions to carry the current. Electrical energy is absorbed to bring about the decomposition into the elements. |
| Liquid hydrogen fluoride can be mixed with potassium fluoride and electrolyzed into hydrogen and fluorine. |
| Synthesis gas, a mixture of hydrogen and carbon monoxide, can be heated to temperatures between 200 and 300 degrees Celsius in the presence of a catalyst. Octane, C8H18, and water are produced. |
| Hydrogen gas burns in oxygen to make water. |
| Hydrochloric acid is poured onto zinc metal to make zinc chloride and hydrogen gas. |
| Zinc replaces the hydrogen in hydrochloric acid, producing zinc chloride solution and hydrogen. |
| In the electrolytic method of preparing a sodium hydroxide solution, direct current is passed through a solution of sodium chloride. Water and sodium chloride react to give hydrogen, chlorine, and sodium hydroxide. |
| Solid potassium metal reacts with water, giving a solution of potassium hydroxide and releasing hydrogen. |
| Metals other than the noble metals such as silver and gold react with acids to produce hydrogen. Aluminum is a metal that reacts with hydrochloric acid to produce aluminum chloride solution and hydrogen. |
| Aluminum added to an aqueous solution of sulfuric acid forms a solution of aluminum sulfate. Hydrogen gas is also released. |
| Calcium metal reacts with water to produce a solution of calcium hydroxide and hydrogen is evolved. |
| In the Haber process for producing ammonia, nitrogen reacts with hydrogen at high temperature and pressure. |
| In an industrial process, hydrogen chloride is prepared by burning hydrogen in an atmosphere of chlorine. |
| Sodium is a soft reactive metal that instantly reacts with water to give hydrogen and a solution of sodium hydroxide. |
| The burning of hydrogen in oxygen yields water vapor. |
| In principle carbon monoxide and hydrogen can be produced from the reaction of coal (which is mostly carbon) with steam. |
| Many chemists thought that the direct combination of nitrogen and hydrogen was impossible, but in 1905 the German chemist Fritz Haber showed that the reaction was feasible. |
| Tungsten metal is used to make incandescent bulb filaments. The metal is produced from the yellow tungsten (VI) oxide by reaction with hydrogen. Water is also made in the process. |
| Methanol, or CH3OH, is prepared industrially from the gas-phase catalytic reaction of carbon monoxide and hydrogen. |
| Hydrocyanic acid can be made by a two-step process. In the second step nitrogen monoxide and methane (CH4) react to give the acid, water vapor, and hydrogen. |
| An alloy of aluminum and magnesium was treated with sodium hydroxide solution and water, in which only the aluminum reacts. Sodium aluminum hydroxide and hydrogen gas are the products. |
| Raoul Pictet, the Swiss physicist who first liquefied oxygen, attempted to liquefy hydrogen. He heated potassium formate with potassium hydroxide in a closed 2.50 L vessel. Hydrogen was produced alongside solid potassium carbonate. |
| Boric acid, a solid, is produced alongside hydrogen gas when diborane (B2H6) combines with water. |
| Metal hydrides react with water to form hydrogen gas and the metal hydroxide. An example is the reaction of strontium hydride with water, which produces strontium hydroxide. |
| The major industrial source of hydrogen gas is the reaction of methane, CH4, and water at high temperatures (800 to 1000 degrees Celsius) and high pressures (10 to 50 atmospheres) with a metallic catalyst, often nickel. Carbon monoxide is a byproduct. |
| Most high explosives are organic compounds that contain nitro (-NO2) groups and produce nitrogen and other gases as products. An example is trinitrotoluene, or TNT (C7H5N3O6), a solid at normal temperatures, but decomposes into carbon monoxide, hydrogen, nitrogen, and solid carbon. |
| Ammonia is used throughout the world as a fertilizer and in making nitrogenous plastics and fibers. It is usually manufactures in the Haber process, the direct reaction of nitrogen and hydrogen in the presence of other compounds that accelerate the reaction. |
| Passing an electric current into brine, a solution of sodium chloride in water, gives hydrogen, chlorine, and aqueous sodium hydroxide. |
| (1) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 4-15 - 4-16. |
| (2) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 10-178 - 10-180. |
| (3) - Atomic Mass Data Center. http://amdc.in2p3.fr/web/nubase_en.html (accessed July 14, 2009). |
| (4) - Silberberg, Martin S. Chemistry: The Molecular Nature of Matter and Change, 4th ed.; McGraw-Hill Higher Education: Boston, MA, 2006, p 965. |
| (5) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 14-17. |
| (6) - Silberberg, Martin S. Chemistry: The Molecular Nature of Matter and Change, 4th ed.; McGraw-Hill Higher Education: Boston, MA, 2006, p 962. |
| (7) - Silberberg, Martin S. Chemistry: The Molecular Nature of Matter and Change, 4th ed.; McGraw-Hill Higher Education: Boston, MA, 2006, p 964. |
| (8) - Morgan, John W. and Anders, Edward, Proc. Natl. Acad. Sci. USA 77, 6973-6977 (1980) |
| (9) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 7-17. |
