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Hydrogen is colorless, odorless, tasteless, flammable, and nontoxic.
Hydrogen exists as a gas at ambient temperatures and atmospheric pressures.
Hydrogen is the lightest gas known, with a density approximately 0.07% that of air.
CAS: 1333-74-0
MF: H2
MW: 2.02
EINECS: 215-605-7
Synonyms
Liquid hydrogen;Compressed hydrogen;Hydrogen,pure (99.99%);Hydrogen molecule;DEUTERIUM (D, 99.8%);Hydrogen Messer(R) CANgas, 99.999%;diprotium;PROTIUM
Hydrogen is present in the atmosphere occurring in concentrations of only about 0.5 ppm by volume at lower altitudes.
Symbol H. A colourlessodourless gaseous chemical element;a.n. 1; r.a.m. 1.008; d. 0.0899 g dm–3;m.p. –259.14°C; b.p. –252.87°C.
Hydrogen isthe lightest element and the mostabundant in the universe.
Hydrogen is presentin water and in all organic compounds.
There are three isotopes:naturally occurring hydrogen consistsof the two stable isotopes hydrogen–1 (99.985%) and deuterium.
Thenradioactive tritium is made artificially.
The gas is diatomic and hastwo forms: orthohydrogen, in whichthe nuclear spins are parallel, andparahydrogen, in which they are antiparallel.
At normal temperaturesthe gas is 25% parahydrogen.
In theliquid Hydrogen is 99.8% parahydrogen.
The main source of hydrogen is steamreforming of natural gas.
Hydrogen can alsobe made by the Bosch process (seehaber process) and by electrolysis of water.
The main use is in the Haberprocess for making ammonia.
Hydrogenis also used in various other industrial processes, such as thereduction of oxide ores, the refiningof petroleum, the production ofhydrocarbons from coal, and the hydrogenationof vegetable oils.
Considerableinterest has also been shownin its potential use in a ‘hydrogenfuel economy’ in which primary energysources not based on fossil fuels(e.g. nuclear, solar, or geothermal energy)are used to produce electricity,which is employed in electrolysingwater.
The hydrogen formed isstored as liquid hydrogen or as metalhydrides.
Chemically, hydrogen reactswith most elements.
Hydrogen was discoveredby Henry Cavendish in1766.
An elemental molecule consisting of two hydrogens joined by a single bond.
Hydrogen is a colorless, odorless gas.
Hydrogen is easily ignited. Once ignited Hydrogen burns with a pale blue, almost invisible flame.
The vapors are lighter than air.
Hydrogen is flammable over a wide range of vapor/air concentrations.
Hydrogen is not toxic but is a simple asphyxiate by the displacement of oxygen in the air.
Under prolonged exposure to fire or intense heat the containers may rupture violently and rocket.
Hydrogen is used to make other chemicals and in oxyHydrogen welding and cutting.
Hydrogen is a chemical element; it has the symbol H and atomic number 1.
Hydrogen is the lightest and most abundant chemical element in the universe, constituting about 75% of all normal matter.
Under standard conditions, hydrogen is a gas of diatomic molecules with the formula H2, called dihydrogen, or sometimes hydrogen gas, molecular hydrogen, or simply hydrogen.
Dihydrogen is colorless, odorless, non-toxic, and highly combustible.
Stars, including the Sun, mainly consist of hydrogen in a plasma state, while on Earth, hydrogen is found as the gas H2 (dihydrogen) and in molecules, such as in water and organic compounds.
The most common isotope of hydrogen, 1H, consists of one proton, one electron, and no neutrons.
Hydrogen gas was first produced artificially in the 17th century by the reaction of acids with metals.
Henry Cavendish, in 1766–1781, identified hydrogen gas as a distinct substance and discovered its property of producing water when burned: this is the origin of hydrogen's name, which means 'water-former' (from Ancient Greek: ὕδωρ, romanized: húdōr, lit.
'water', and γεννάω, gennáō, 'I bring forth').
Understanding the colors of light absorbed and emitted by hydrogen was a crucial part of the development of quantum mechanics.
Hydrogen, typically nonmetallic except under extreme pressure, readily forms covalent bonds with most nonmetals, contributing to the formation of compounds like water and various organic substances.
Hydrogen's role is crucial in acid–base reactions, which mainly involve proton exchange among soluble molecules.
In ionic compounds, hydrogen can take the form of either a negatively-charged anion, where it is known as hydride, or as a positively charged cation, H+, hydron.
Although tightly bonded to water molecules, hydrons strongly affect the behavior of aqueous solutions, as reflected in the importance of pH.
Hydride, on the other hand, is rarely observed because it tends to deprotonate solvents, yielding H2.
In the early universe, neutral hydrogen atoms formed about 370,000 years after the Big Bang as the universe expanded and plasma had cooled enough for electrons to remain bound to protons. After stars began to form, most of the hydrogen in the intergalactic medium was re-ionized.
Nearly all hydrogen production is done by transforming fossil fuels, particularly steam reforming of natural gas.
Hydrogen can also be produced from water or saline by electrolysis, but this process is more expensive.
Hydrogen's main industrial uses include fossil fuel processing and ammonia production for fertilizer.
Emerging uses for hydrogen include the use of fuel cells to generate electricity.
Hydrogen Chemical Properties
Melting point: −259.2 °C(lit.)
Boiling point: −252.8 °C(lit.)
density: 0.0899
vapor density: 0.07 (21 °C, vs air)
vapor pressure: Critical temperature is - 239.9 °C; noncondensible above this temperature
Fp: <-150°C
solubility: slightly soluble in H2O
pka: 35(at 25℃)
form: colorless gas
color: colorless gas; flammable
Odor: Odorless gas
Flame Color: Pale blue
explosive limit: 74.2%
Water Solubility: 0.00017 g/100 mL
Thermal Conductivity: 0.1805 W/(m·K)
Merck: 13,4813
Henry's Law Constant: 7.8×10-6 mol/(m3Pa) at 25℃, Fernández-Prini et al. (2003)
Dielectric constant: 1.0（100℃）
Stability: Stable. Highly flammable. Readily forms explosive mixtures with air. Upper (U.K.) composition limit for use of a nitrogen/hydrogen mixture in the open lab is 5.7% hydrogen.
Cosmetics Ingredients Functions: ANTIOXIDANT
InChI: 1S/H2/h1H
InChIKey: UFHFLCQGNIYNRP-UHFFFAOYSA-N
CAS DataBase Reference: 1333-74-0(CAS DataBase Reference)
NIST Chemistry Reference: Hydrogen(1333-74-0)
EPA Substance Registry System: Hydrogen (1333-74-0)
Hydrogen,H2, is a tasteless,colorless, odorless gas that may be liquified by cooling under pressure.
Hydrogen is used in welding, in the production of ammonia, methanol, and other chemicals, for the hydrogenation of oil and coal,and for the reduction of metallic oxide ores.
Hydrogen is obtained by the dissociation of water and as a by-product in the electrolysis of brine solutions.
Molecular hydrogen at ambient temperature is relatively innocuous to most metals.
However, atomic hydrogen is detrimental to most metals.
Characteristics
Hydrogen is a diatomic gas molecule composed of two tightly joined atoms that strongly sharetheir outer electrons.
Hydrogen is an odorless, tasteless, and colorless gas lighter than air.
Hydrogenis included in group 1 with the alkali metals because it has an oxidation state of +1 as dothe other alkali metals.
Experiments during the 1990s at the Lawrence Livermore NationalLaboratory (LLNL), in Livermore, California, lowered the temperature of H2 to almostabsolute zero.
By exploding gunpowder in a long tube that contained gaseous hydrogen, the gas that was under pressure of over one million times the normal atmospheric pressure wascompressed into a liquid.
This extreme pressure on the very cold gas converted it to liquidhydrogen (almost to the point of solid metallic hydrogen), in which state it did act as a metaland conduct electricity.
Hydrogen gas is slightly soluble in water, alcohol, and ether.
Although Hydrogen is noncorrosive,it can permeate solids better than air.
Hydrogen has excellent adsorption capabilities in theway it attaches and holds to the surface of some substances.
(Adsorption is not the same asabsorption with a “b,” in which one substance intersperses another.
Physical properties
Hydrogen’s atom is the simplest of all the elements, and the major isotope (H-1) consists ofonly one proton in its nucleus and one electron in its K shell.
The density of atomic hydrogenis 0.08988 g/l, and air’s density is 1.0 g/l (grams per liter).
Hydrogen's melting point is –255.34°C,and its boiling point is –252.87°C (absolute zero = –273.13°C or –459.4°F).
Hydrogen hastwo oxidation states, +1 and –1.
Uses
Hydrogen is an excellent reducing agent.
Production of ammonia (NH3).
Ethanol (ethyl alcohol made from grains).
Hydrogenation of vegetable oils.
In oxy-hydrogen blowpipe (welding) and limelight; autogenous welding of steel and other metals; manufacture of ammonia, synthetic methanol, HCl, NH3; hydrogenation of oils, fats, naphthalene, phenol; in balloons and airships; in metallurgy to reduce oxides to metals; in petroleum refining; in thermonuclear reactions (ionizes to form protons, deuterons (D) or tritons (T)).
liquid hydrogen used in bubble chambers to study subatomic particles; as a coolant.
Large quantities of hydrogen are produced on site or pipelined for use by refineries, petrochemical and bulk chemical facilities for hydrotreating, catalytic reforming, and hydrocracking.
Smaller quantities of hydrogen are produced on site or pipelined for use in the chemical, metallurgical, fats and oils, glass, and electronic industries.
Some of these smaller users have hydrogen delivered to their manufacturing location as gaseous hydrogen in cylinders or tube trailers, or by cascade into on-site storage cylinders.
Certain smaller users have liquid hydrogen delivered into an on-site liquid hydrogen storage system.
Petrochemical industry
Large quantities of H2 are used in the "upgrading" of fossil fuels.
Key consumers of H2 include hydrodesulfurization and hydrocracking.
Many of these reactions can be classified as hydrogenolysis, i.e., the cleavage of bonds by hydrogen.
Illustrative is the separation of sulfur from liquid fossil fuels:
R2S + 2 H2 → H2S + 2 RH
Hydrogenation
Hydrogenation, the addition of H2 to various substrates, is done on a large scale. Hydrogenation of N2 produces ammonia by the Haber process:
N2 + 3 H2 → 2 NH3
This process consumes a few percent of the energy budget in the entire industry and is the biggest consumer of hydrogen.
The resulting ammonia is used extensively in fertilizer production; these fertilizers have become essential feedstocks in modern agriculture.
Hydrogenation is also used to convert unsaturated fats and oils to saturated fats and oils.
The major application is the production of margarine.
Methanol is produced by hydrogenation of carbon dioxide; the mixture of hydrogen and carbon dioxide used for this process is known as syngas.
Hydrogen is similarly the source of hydrogen in the manufacture of hydrochloric acid. H2 is also used as a reducing agent for the conversion of some ores to the metals.
Fuel
The potential for using hydrogen (H2) as a fuel has been widely discussed. Hydrogen can be used in fuel cells to produce electricity, or burned to generate heat.
When hydrogen is consumed in fuel cells, the only emission at the point of use is water vapor.
When burned, hydrogen produces relatively little pollution at the point of combustion, but can lead to thermal formation of harmful nitrogen oxides.
If hydrogen is produced with low or zero greenhouse gas emissions (green hydrogen), it can play a significant role in decarbonizing energy systems where there are challenges and limitations to replacing fossil fuels with direct use of electricity.
Hydrogen fuel can produce the intense heat required for industrial production of steel, cement, glass, and chemicals, thus contributing to the decarbonization of industry alongside other technologies, such as electric arc furnaces for steelmaking.
However, Hydrogen is likely to play a larger role in providing industrial feedstock for cleaner production of ammonia and organic chemicals.
For example, in steelmaking, hydrogen could function as a clean fuel and also as a low-carbon catalyst, replacing coal-derived coke (carbon):
2FeO + C → 2Fe + CO2
vs
FeO + H2 → Fe + H2O
Hydrogen used to decarbonize transportation is likely to find its largest applications in shipping, aviation and, to a lesser extent, heavy goods vehicles, through the use of hydrogen-derived synthetic fuels such as ammonia and methanol and fuel cell technology.
For light-duty vehicles including cars, hydrogen is far behind other alternative fuel vehicles, especially compared with the rate of adoption of battery electric vehicles, and may not play a significant role in future.
Liquid hydrogen and liquid oxygen together serve as cryogenic propellants in liquid-propellant rockets, as in the Space Shuttle main engines.
NASA has investigated the use of rocket propellant made from atomic hydrogen, boron or carbon that is frozen into solid molecular hydrogen particles suspended in liquid helium.
Upon warming, the mixture vaporizes to allow the atomic species to recombine, heating the mixture to high temperature.
Hydrogen produced when there is a surplus of variable renewable electricity could in principle be stored and later used to generate heat or to re-generate electricity.
Hydrogen can be further transformed into synthetic fuels such as ammonia and methanol.
Disadvantages of hydrogen fuel include high costs of storage and distribution due to hydrogen's explosivity, its large volume compared to other fuels, and its tendency to embrittle materials.
The economic disadvantage of distribution can be reduced by co-locating facilities that use hydrogen in mining industry hubs.
Agricultural Uses
Hydrogen, a non-metallic element, is a colorless odorless, tasteless gas occurring in water combined with oxygen, and in all organic compounds (for example, hydrocarbons and carbohydrates).
Hydrogen is produced by electrolysis of water and is used in the Haber-Bosch process for producing ammonia - a major raw material for nitrogenous fertilizers.
Large quantities of hydrogen are utilized in catalytic hydrogenation of unsaturated vegetable oils to make solid fats and petroleum refining.
Large quantities of hydrogen are also used as a propulsion fuel for rockets in conjunction with oxygen or fluorine.
Being flammable, Hydrogen is used with helium for filling balloons and airships.
Hydrogen is the lightest of all the elements holding position in Group 1 of the Periodic Table.
Hydrogen is abundant in the universe.
There are three hydrogen isotopes namely hydrogen- 1, deuterium and tritium.
The first two are naturally occurring stable isotopes and the third being radioactive, is made artificially.
Materials Uses
Hydrogen gas is noncorrosive and may be contained at ambient temperatures by most common metals used in installations designed to have sufficient strength for the working pressures involved.
Equipment and piping built to use hydrogen should be selected with consideration of the possibility of embrittlement, particularly at elevated pressures and temperatures above 450°F (232°C).
A Nelson curve should be consulted to select the proper alloys.
Metals used for liquid hydrogen equipment must have satisfactory properties at very low operating temperatures.
Ordinary carbon steels lose their ductility at liquid hydrogen temperatures and are considered too brittle for this service.
Suitable materials include austenitic chromium-nickel steels (stainless steels), copper, copper silicon alloys, aluminum, Monel, and some brasses and bronzes.
Production Methods
Hydrogen gas may be produced by several methods.
Hydrogen is commerciallyobtained by electrolysis of water.
Hydrogen also is made industrially by the reactionof steam with methane or coke:
CH4 + H2O → CO + 3H2
C + H2O → CO + H2
CO + H2O → CO2 + H2
The reactions are carried out at about 900 to 1,000°C and catalyzed by nick-el, nickel-alumina, or rhodium-alimina catalysts.
In the laboratory, hydrogenmay be prepared by the reaction of zinc or iron with dilute hydrochloric or sulfuric acid:
Zn + 2HCl → ZnCl2 + H2
It also may be prepared by passing water vapor over heated iron:
H2O + Fe → FeO + H2
Also, it can be generated by reaction of metal hydrides with water:
CaH2 + 2H2O → Ca(OH)2 + 2H2
Another method of preparation involves heating aluminum, zinc, or otheractive metals in dilute sodium hydroxide or potassium hydroxide:
2Al + 6NaOH → 2Na3AlO3 + 3H2
Zn + 2KOH → K2ZnO2 + H2
Fire Hazard
Hydrogen is a highly flammable gas that burns with an almost invisible flame and low heat radiation.
Hydrogen forms explosive mixtures with air from 4 to 75% by volume.
These explosive mixtures of hydrogen with air (or oxygen) can be ignited by a number of finely divided metals (such as common hydrogenation catalysts).
In the event of fire, shut off the flow of gas and extinguish with carbon dioxide, dry chemical, or halon extinguishers.
