Chemical Fact Sheet
Hydrogen
| Chemical Abstract Number (CAS #) | 1333-74-0 |
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| Synonyms | MOLECULAR-HYDROGEN-;H-;PROTIUM |
| Analytical Methods | N/A |
| Molecular Formula | H2 |
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Synopsis
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Hydrogen - (Gr. hydro, water, and genes, forming), H; at. wt. 1.00794(7); at. no. 1; m.p. -259.34 deg C; b.p. -252.87 deg C; density 0.08988 g/l; density (liquid) 70.8 g/l (-253 deg C); density (solid) 70.6 g/l (-262 deg C); valence 1. 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/cu cm. 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 cu. ft. of hydrogen gas is about 0.076 lb at 0deg 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 weioht 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 deg 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 waters, 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. |
| Use | OXYHYDROGEN FLAME IS USED IN PROCESSING OF QUARTZ; IN PRODN OF SEVERAL METALS WHICH RESIST FUSION, SUCH AS MOLYBDENUM, BISMUTH CHEM INT FOR AMMONIA & OTHER CHEMS (EG, METHANOL, CYCLOHEXANE); CHEM INT & REDUCING AGENT IN METAL PROCESSING; FEEDSTOCK PURIFICATION IN PETROLEUM REFINING; PRODUCTION OF LUBRICATING OILS IN OXY-HYDROGEN BLOWPIPE (WELDING) & LIMELIGHT; AUTOGENOUS WELDING OF STEEL & OTHER METALS; MFR SYNTHETIC METHANOL, HYDROGEN CHLORIDE; HYDROGENATION OF OILS, FATS, NAPHTHALENE, PHENOL, TUNGSTEN; IN BALLOONS & AIRSHIPS; IN THERMONUCLEAR REACTIONS: HYDROGEN ATOM IONIZES TO FORM PROTONS, DEUTERONS (D) OR TRITONS (T) IN BUBBLE CHAMBERS TO STUDY SUBATOMIC PARTICLES; AS A COOLANT /LIQUID HYDROGEN/ IN CRYOGENICS; IN STUDY OF SUPERCONDUCTIVITY /LIQUID HYDROGEN/ PRODUCTION OF ETHANOL AND ANILINE; HYDROCRACKING, HYDROFORMING & HYDROFINING OF PETROLEUM; HYDROGENOLYSIS OF COAL; REDUCING AGENT FOR ORG SYNTHESIS & METALLIC ORES; REDUCING ATMOSPHERES TO PREVENT OXIDATION; MAKING HYDROGEN BROMIDE; PRODN OF HIGH-PURITY METALS; PROPELLANT; FUEL FOR NUCLEAR ROCKET ENGINES FOR HYPERSONIC TRANSPORT; MISSILE FUEL ROCKET FUEL |
| Consumption Patterns | CHEMICAL INTERMEDIATE FOR AMMONIA, 56%; PETROLEUM REFINING, 25%; CHEMICAL INTERMEDIATE FOR METHANOL, 7%; OTHER, 12% (1980) |
| Apparent Color | COLORLESS GAS; CUBIC SOLID |
| Boiling Point | -252.77 DEG C |
| Melting Point | -259.2 DEG C @ 54 MM HG
Mp: 13.947 K; bp: 20.380 K; critical temp: 33.18 K; critical pressure: 1315 kPa; Critical volume: 66.949 cu cm/mol; density @ bp: 0.03520 mol/cu cm; density @ mp: 0.03830 mol/cu cm; compressibility factor @ mp: 0.0011621, @ bp: 0.01698; @ critical point: 0.3191; adiabatic compressibility @ triple point: 0.00813 MPa, @ bp: 0.0119 MPa; coefficient of volume expansion @ triple point: 0.0102 K, @ bp: 0.0164 K; heat of vaporization @ triple point: 911.3 J/mol, @ bp: 899.1 J/mol; critical pressure @ triple point: 13.23 J/mol.K, @ bp: 19.70 J/mol.K; critical volume @ triple point: 9.53 J/mol.K, @ bp: 11.60 J/mol.K; enthalpy @ triple point: 438.7 J/mol, @ bp: 548.3 J/mol; internal energy @ triple point: 435.0 J/mol, @ bp: 545.7 J/mol; entropy @ triple point: 28.7 J/mol.K, @ bp: 34.92 J/mol.K; velocity of sound @ triple point: 1282 m/sec, @ bp: 1101 m/sec; viscosity @ triple point: 0.0256 cP, @ bp: 0.0133 cP; thermal conductivity @ triple point: 0.74 mW/cm.K, @ bp: 1.00 mW/cm.K; dielectric constant @ triple point: 1.253, @ bp: 1.231; surface tension @ triple point: 3.00 mN/m, @ bp: 1.94 mN/m; isothermal compressibility @ triple point: -0.0110 MPa, @ bp: -0.0199 MPa Mp: 13.947 K; vapor pressure @ mp: 7.20 kPa; vapor pressure @ 10 K: 0.231 kPa; density @ mp: 43.01X10+3 mol/cu cm; heat of fusion @ mp: 117.2 J/mol; heat of sublimation @ mp: 1028.4 J/mol; critical pressure @ 10 K: 20.79 J/mol.K; enthalpy @ mp: 321.6 J/mol; internal energy @ mp: 317.9 J/mol; entropy @ mp: 20.3 J/mol.K; thermal conductivity @ mp: 9.0 mW/cm.K; dielectric constant @ mp: 1.287; heat of dissociation @ 0 K: 430.889 kJ/mol . Dipole moment: 0 |
| Molecular Weight | 2.02 |
| Density | 0.069 (GAS) (AIR= 1); 0.0700 @ BP (LIQ); 0.0763 @ 13 K (SOLID) |
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Chemical and Physical Properties |
ATOMIC NUMBER 1; VALENCE 1; ELEMENTAL STATE: H2; ISOTOPES: (1)H (PROTIUM 99.9844%), (2)H (DEUTERIUM 0.0156%), (3)H (TRITIUM, TRACES ONLY); IONIZATION POTENTIAL OF H ATOM IS 13.59 ELECTRON VOLTS; ACCELERATED PROTONS BRING ABOUT EXTREMELY VARIED NUCLEAR REACTIONS; 1 L OF GAS @ 0 DEG C WEIGHS 0.08987 G LIGHTEST OF ALL GASES; LIFTING POWER OF 1 CU FT HYDROGEN GAS IS ABOUT 0.076 LB @ 0 DEG C, 760 MM HG MP & BP OF PARA-HYDROGEN ARE ABOUT 0.1 DEG C LOWER THAN THOSE OF NORMAL HYDROGEN ORTHO-HYDROGEN MOLECULES HAVE A PARALLEL SPIN; PARA, AN ANTIPARALLEL SPIN BURNS WITH PALE BLUE FLAME IN PRESENCE OF OXYGEN TRIPLE POINT TEMP: 13.8 DEG K; TRIPLE POINT PRESSURE: 0.069 ATM; HEAT OF FUSION: 13.9 CAL/G; CRITICAL TEMP: 33 K; CRITICAL PRESSURE: 12.4 ATM; HEAT OF VAPORIZATION: 106.5 CAL/G /P-HYDROGEN/ TRIPLE POINT TEMP: 13.9 K; TRIPLE POINT PRESSURE: 0.071 ATM /N-HYDROGEN/ SPECIFIC VOLUME: 193 CU FT/LB @ 21.1 DEG C; DIATOMIC GAS Heat of fusion: 28 cal/g mole Forms cmpd with almost every other element Compressibility factor @ 0 deg C: 1.00042; adiabatic compressibility @ 300 K: 7.03 MPa; coefficient of volume expansion @ 300 K: 0.00333/K; critical volume @ 0 deg C: 20.30 J/mol.K; enthalpy @ 0 deg C: 7749.2 J/mol; internal energy @ 0 deg C: 5477.1 J/mol; entropy @ 0 deg C: 139.59 J/mol.K; velocity of sound @ 0 deg C: 1246 m/sec; thermal conductivity @ 0 deg C: 1.739 mW/cm.K; dielectric constant @ 0 deg C: 1.000271; isothermal compressibility @ 300 K: -9.86 MPa; self diffusion coefficient @ 0 deg C: 1.285 sq cm/sec; gas diffusivity in water @ 25 deg C: 4.8X10-5 sq cm/sec; Lennard-Jones parameters: collision diameter, 2.928X10+10 m, interaction parameter, 37.00 K; heat of dissociation @ 298.16 K: 435.881 kJ/mol |
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Environmental Fate |
HYDROGEN OCCURS CHIEFLY IN COMBINATION WITH OXYGEN IN WATER, BUT IT IS ALSO PRESENT IN ORG MATTER SUCH AS LIVING PLANTS, PETROLEUM, COAL ETC. IT IS PRESENT AS FREE ELEMENT IN THE ATMOSPHERE, BUT ONLY TO THE EXTENT OF LESS THAN 1 PPM, BY VOLUME. HYDROGEN FROM NATURAL SOURCES CONSISTS OF MORE THAN 99.8% PROTIUM. |
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