Hydrogen - what is it? Properties and meaning. Covalent and organic compounds

In 1766, the English chemist G. Cavendish collected “combustible air” displaced by metals from acids and studied its properties. But only 15 years later it was proven that this “air” is part of water, and it was given the name “hydrogenium”, i.e. “giving birth to water”, “hydrogen”.

The share of hydrogen on Earth, including water and air, accounts for about 1% by mass. This is a very common and vital element. It is part of all plants and animals, as well as the most common substance on Earth - water.

Hydrogen is the most common element in the Universe. It stands at the beginning of a long and complex process of synthesis of elements in stars.

Solar energy is the main source of life on Earth. And the fundamental principle of this energy is thermonuclear reaction, occurring on the Sun in several stages. Its result is the formation of 4 hydrogen nuclei - protons - one helium nucleus and two positrons. This releases a huge amount of energy.

Man managed to reproduce on Earth a not very accurate semblance of the main solar reaction. Under terrestrial conditions, we can force only the heavy isotopes of hydrogen 2H - deuterium and 3H - tritium to enter into such a reaction. Ordinary hydrogen with atomic mass 1 - protium - is beyond our control in this sense. Controlled thermonuclear fusion as a limitless source of peaceful energy is not yet available to humans.

Hydrogen occupies a special place in the periodic table of elements. This is the element from which the periodic table begins. It usually stands in group I above lithium. Because the hydrogen atom has only one valence electron (and one electron in general). However, in modern editions of the periodic table, hydrogen is also placed in group VII above fluorine, since hydrogen has something in common with halogens. In addition, hydrogen is capable of forming compounds with metals - hydrides. In practice, the most important of these is the compound of lithium with heavy hydrogen, deuterium.

Isotopes of all elements have almost identical basic physical and chemical properties. But for the isotopes of hydrogen - protium, deuterium and tritium - they differ quite significantly. For example, the boiling points of protium, deuterium and tritium differ by several degrees. Therefore, isotopes of hydrogen are easier to separate than isotopes of any other element.

Hydrogen is a colorless gas, tasteless and odorless. It is the lightest of all gases, 14.4 times lighter than air. Hydrogen becomes liquid at -252.6°C and solid at -259.1°C.

Under normal conditions, the chemical activity of hydrogen is low; it reacts with fluorine, iodine and chlorine. But at elevated temperatures, hydrogen reacts with bromine, iodine, sulfur, selenium, tellurium, and in the presence of catalysts, with nitrogen, forming ammonia NH3. A mixture of 2 volumes of H2 and 1 volume of O2 - it is called detonating gas - explodes violently when ignited. Hydrogen burns in oxygen with a non-luminous flame, forming water.

At high temperatures, hydrogen is able to “remove” oxygen from the molecules of many compounds, including most metal oxides. For a chemist, hydrogen is, first of all, an excellent reducing agent, although it is still quite expensive. And it’s not easy to work with him. Therefore, on an industrial scale, reduction with hydrogen (for example, metals from oxides) is used very limitedly.

Hydrogen is widely used in the process of hydrogenation - the transformation of liquid fats into solid ones, for example, to obtain edible margarine from vegetable oils, as well as in a number of chemical syntheses. The largest consumers of hydrogen in chemical industry Ammonia and methyl alcohol production still remains.

There is increasing interest these days in hydrogen as a source of thermal energy. Indeed, the combustion of pure hydrogen releases significantly more heat than the combustion of the same amount of any fuel. Even designs for hydrogen fueled cars have appeared. In most of them, the source of hydrogen is solid hydrides of certain metals, which, under certain conditions, firmly retain the hydrogen bound to them. But as soon as these conditions are changed, for example, the temperature is increased above some, usually quite low, threshold, and hydrogen begins to be released into a device that replaces a carburetor in such a car. Of course, many still stand in the way of creating a mass-produced hydrogen car. technical difficulties. But, apparently, they will be overcome soon enough, since such fuel is energetically beneficial. In addition, combustion does not produce hydrogen. harmful impurities polluting the atmosphere, but only clean water is obtained.

Hydrogen is a chemical element with the symbol H and atomic number 1. With a standard atomic weight of about 1.008, hydrogen is the lightest element on the periodic table. Its monatomic form (H) is the most abundant chemical in the Universe, accounting for approximately 75% of the total baryon mass. Stars are mainly composed of hydrogen in a plasma state. The most common isotope of hydrogen, called protium (this name is rarely used, symbol 1H), has one proton and no neutrons. The widespread appearance of atomic hydrogen first occurred during the era of recombination. At standard temperatures and pressures, hydrogen is a colorless, odorless, tasteless, non-toxic, non-metallic, flammable diatomic gas with molecular formula H2. Because hydrogen readily forms covalent bonds with most nonmetallic elements, most hydrogen on Earth exists in molecular forms such as water or organic compounds. Hydrogen plays a particularly important role in acid-base reactions because most acid-based reactions involve the exchange of protons between soluble molecules. In ionic compounds, hydrogen can take the form of a negative charge (i.e., an anion), where it is known as a hydride, or as a positively charged (i.e., cation) form, denoted by the symbol H+. The hydrogen cation is described as consisting of a simple proton, but in reality hydrogen cations in ionic compounds are always more complex. As the only neutral atom for which the Schrödinger equation can be solved analytically, hydrogen (namely, the study of the energetics and bonding of its atom) played a key role in the development of quantum mechanics. Hydrogen gas was first produced artificially in the early 16th century by reacting acids with metals. In 1766-81. Henry Cavendish was the first to recognize that hydrogen gas was a discrete substance, and that it produced water when burned, giving it its name: in Greek, hydrogen means "water producer". Industrial hydrogen production primarily involves steam conversion of natural gas and, less commonly, more energy-intensive methods such as water electrolysis. Most of Hydrogen is used close to where it is produced, with the two most common uses being fossil fuel processing (eg hydrocracking) and ammonia production, mainly for the fertilizer market. Hydrogen is a concern in metallurgy because it can make many metals brittle, making the design of pipelines and storage tanks difficult.

Properties

Combustion

Hydrogen gas (dihydrogen or molecular hydrogen) is a flammable gas that will burn in air over a very wide range of concentrations from 4% to 75% by volume. The enthalpy of combustion is 286 kJ/mol:

2 H2 (g) + O2 (g) → 2 H2O (l) + 572 kJ (286 kJ/mol)

Hydrogen gas forms explosive mixtures with air in concentrations from 4-74% and with chlorine in concentrations up to 5.95%. Explosive reactions can be caused by sparks, heat or sunlight. The autoignition temperature of hydrogen, the temperature at which it ignites spontaneously in air, is 500 °C (932 °F). Pure hydrogen-oxygen flames emit ultraviolet radiation and with a high oxygen mixture are almost invisible to the naked eye, as evidenced by the faint plume of the Space Shuttle main engine compared to the highly visible plume of the Space Shuttle Solid Rocket Booster, which uses an ammonium perchlorate composite. A flame detector may be required to detect a burning hydrogen leak; such leaks can be very dangerous. A hydrogen flame is blue under other conditions, and resembles the blue flame of natural gas. The death of the airship "Hindenburg" is a sad famous example burning hydrogen, and the matter is still under discussion. The visible orange flames in this incident were caused by exposure to a mixture of hydrogen and oxygen combined with carbon compounds from the skin of the airship. H2 reacts with every oxidizing element. Hydrogen can react spontaneously when room temperature with chlorine and fluorine to form the corresponding hydrogen halides, hydrogen chloride and hydrogen fluoride, which are also potentially dangerous acids.

Electron energy levels

The ground state energy level of an electron in a hydrogen atom is −13.6 eV, which is equivalent to an ultraviolet photon with a wavelength of about 91 nm. Energy levels hydrogen can be calculated quite accurately using the Bohr model of the atom, which conceptualizes the electron as an "orbital" proton, analogous to earth's orbit Sun. However, the atomic electron and proton are held together electromagnetic force, and planets and celestial objects are held together by gravity. Due to the discretization of angular momentum postulated in early quantum mechanics by Bohr, the electron in Bohr's model can only occupy certain allowable distances from the proton and therefore only certain allowable energies. A more accurate description of the hydrogen atom comes from a purely quantum mechanical treatment, which uses the Schrödinger equation, the Dirac equation, or even the Feynman integrated circuit to calculate the probability density distribution of an electron around a proton. The most sophisticated processing methods can produce small effects of special relativity and vacuum polarization. In quantum machining, the electron in a hydrogen atom has no ground state at all torque, which illustrates how " planetary orbit" is different from the movement of an electron.

Elementary molecular forms

There are two different spin isomers of diatomic hydrogen molecules, which differ in the relative spin of their nuclei. In the orthohydrogen form, the spins of the two protons are parallel and form a triplet state with a molecular spin quantum number of 1 (1/2 + 1/2); in the form of parahydrogen, the spins are antiparallel and form a singlet with a molecular spin quantum number of 0 (1/2 1/2). At standard temperature and pressure, hydrogen gas contains about 25% para form and 75% ortho form, also known as the "normal form". The equilibrium ratio of orthohydrogen to parahydrogen depends on temperature, but since the ortho form is an excited state and has higher energy than the para form, it is unstable and cannot be purified. At very low temperatures, the equilibrium state consists almost exclusively of the para form. Thermal properties The liquid and gas phases of pure parahydrogen differ significantly from the normal form properties due to differences in rotational heat capacities, which is discussed in more detail in spin isomers of hydrogen. Ortho/pairwise distinction is also found in other hydrogen-containing molecules or functional groups, such as water and methylene, but this has little significance for their thermal properties. Uncatalyzed interconversion between para and ortho H2 increases with increasing temperature; thus, rapidly condensed H2 contains large amounts of orthogonal form high energies, which very slowly converts to the para form. The ortho/para coefficient in condensed H2 is important factor in the preparation and storage of liquid hydrogen: the conversion from ortho to vapor is exothermic and provides sufficient heat to vaporize some of the hydrogen liquid, resulting in loss of liquefied material. Catalysts for ortho-para conversion, such as iron oxide, Activated carbon, platinized asbestos, rare earth metals, uranium compounds, chromium oxide or some nickel compounds are used in hydrogen cooling.

Phases

Hydrogen gas

Liquid hydrogen

Sludge hydrogen

Solid hydrogen

Metallic hydrogen

Connections

Covalent and organic compounds

While H2 is not very reactive under standard conditions, it forms compounds with most elements. Hydrogen can form compounds with elements that are more electronegative, such as halogens (eg F, Cl, Br, I) or oxygen; in these compounds, hydrogen takes on a partial positive charge. When bonding with fluorine, oxygen or nitrogen, hydrogen can participate in the form of a non-covalent bond medium strength with the hydrogen of other similar molecules, a phenomenon called hydrogen bonding, which has crucial for the stability of many biological molecules. Hydrogen also forms compounds with less electronegative elements such as metals and metalloids, where it takes on a partial negative charge. These compounds are often known as hydrides. Hydrogen forms a wide variety of compounds with carbon, called hydrocarbons, and an even larger variety of compounds with heteroatoms, which, due to their general communication with living things are called organic compounds. Is studying their properties organic chemistry, and their study in the context of living organisms is known as biochemistry. By some definitions, "organic" compounds must contain only carbon. However, most of them also contain hydrogen, and because it is the carbon-hydrogen bond that gives this class of compounds most of their specific chemical characteristics, carbon-hydrogen bonds are required in some definitions of the word "organic" in chemistry. Millions of hydrocarbons are known, and they are usually formed through complex synthetic pathways that rarely involve elemental hydrogen.

Hydrides

Hydrogen compounds are often called hydrides. The term "hydride" assumes that the H atom has taken on a negative or anionic character, designated H-, and is used when hydrogen forms a compound with a more electropositive element. The existence of a hydride anion, proposed by Gilbert N. Lewis in 1916 for the salt-containing hydrides of groups 1 and 2, was demonstrated by Moers in 1920 by electrolysis of molten lithium hydride (LiH), producing a stoichiometric amount of hydrogen at the anode. For hydrides other than Group 1 and 2 metals, the term is misleading given the low electronegativity of hydrogen. The exception to group 2 hydrides is BeH2, which is polymeric. In lithium aluminum hydride, the AlH-4 anion bears hydride centers firmly attached to Al(III). Although hydrides can form in almost all main group elements, the number and combination possible connections vary greatly; for example, more than 100 binary borane hydrides and only one binary aluminum hydride are known. Binary indium hydride has not yet been identified, although there are large complexes. In inorganic chemistry, hydrides can also serve as bridging ligands that link two metal centers in a coordination complex. This function is particularly characteristic of group 13 elements, especially in boranes (boron hydrides) and aluminum complexes, as well as in clustered carboranes.

Protons and acids

Oxidation of hydrogen removes its electron and produces H+, which contains no electrons and a nucleus that usually consists of a single proton. This is why H+ is often called a proton. This species is central to the discussion of acids. According to the Bronsted-Lowry theory, acids are proton donors and bases are proton acceptors. The bare proton, H+, cannot exist in solution or in ionic crystals because of its irresistible attraction to other atoms or molecules with electrons. Except for the high temperatures associated with plasma, such protons cannot be removed from the electron clouds of atoms and molecules and will remain attached to them. However, the term "proton" is sometimes used metaphorically to refer to positively charged or cationic hydrogen attached to other species in this manner, and as such is referred to as "H+" without any implication that any individual protons exist freely as a species. To avoid the appearance of a naked "solvated proton" in solution, acidic aqueous solutions are sometimes thought to contain a less unlikely fictitious species called the "hydronium ion" (H3O+). However, even in this case, such solvated hydrogen cations are more realistically perceived as organized clusters that form species close to H9O+4. Other oxonium ions are found when water is in acidic solution with other solvents. Despite its exotic appearance on Earth, one of the most common ions in the Universe is H+3, known as protonated molecular hydrogen or trihydrogen cation.

Isotopes

Hydrogen has three naturally occurring isotopes, designated 1H, 2H and 3H. Other, highly unstable nuclei (4H to 7H) have been synthesized in the laboratory but have not been observed in nature. 1H is the most abundant isotope of hydrogen with an abundance of over 99.98%. Because this isotope's nucleus consists of only one proton, it is given the descriptive but rarely used formal name protium. 2H, another stable isotope of hydrogen, is known as deuterium and contains one proton and one neutron in its nucleus. It is believed that all the deuterium in the Universe was produced during big bang and has existed from that time until now. Deuterium is not a radioactive element and does not pose a significant toxicity risk. Water enriched with molecules that include deuterium instead of normal hydrogen is called heavy water. Deuterium and its compounds are used as a non-radioactive tracer in chemical experiments and in solvents for 1H-NMR spectroscopy. Heavy water is used as a neutron moderator and coolant for nuclear reactors. Deuterium is also a potential fuel for commercial nuclear fusion. 3H is known as tritium and contains one proton and two neutrons in the nucleus. It is radioactive, decaying to helium-3 via beta decay with a half-life of 12.32 years. It is so radioactive that it can be used in luminous paint, making it useful in making watches with luminous dials, for example. The glass prevents small amounts of radiation from escaping. Small amounts of tritium are formed naturally when cosmic rays interact with atmospheric gases; tritium was also released during nuclear weapons testing. It is used in nuclear fusion reactions as an indicator of isotope geochemistry and in specialized self-powered lighting devices. Tritium has also been used in chemical and biological tagging experiments as a radioactive tracer. Hydrogen is the only element that has different names for its isotopes that are widely used today. During early learning radioactivity, various heavy radioactive isotopes were given their own names, but such names are no longer used, with the exception of deuterium and tritium. The symbols D and T (instead of 2H and 3H) are sometimes used for deuterium and tritium, but the corresponding symbol for protium P is already used for phosphorus and is therefore not available for protium. In its nomenclature guidelines, the International Union of Pure and Applied Chemistry allows the use of any of the symbols D, T, 2H, and 3H, although 2H and 3H are preferred. The exotic atom muonium (symbol Mu), consisting of an antimuon and an electron, is also sometimes considered to be a light radioisotope of hydrogen due to the mass difference between the antimuon and the electron, which was discovered in 1960. During the muon lifetime, 2.2 μs, muonium can be incorporated into compounds such as muonium chloride (MuCl) or sodium muonide (NaMu), similar to hydrogen chloride and sodium hydride, respectively.

Story

Opening and Use

In 1671, Robert Boyle discovered and described the reaction between iron filings and dilute acids that produces hydrogen gas. In 1766, Henry Cavendish was the first to recognize hydrogen gas as a discrete substance, calling the gas "flammable air" due to its metal-acid reaction. He theorized that "flammable air" was virtually identical to a hypothetical substance called "phlogiston", and again discovered in 1781 that the gas produced water when burned. It is believed that he was the one who discovered hydrogen as an element. In 1783, Antoine Lavoisier gave the element the name hydrogen (from the Greek ὑδρο-hydro meaning "water" and -γενής genes meaning "creator") when he and Laplace reproduced Cavendish's data that burning hydrogen produced water. Lavoisier produced hydrogen for his conservation of mass experiments by reacting a stream of steam with metallic iron through an incandescent lamp heated by fire. Anaerobic oxidation of iron by water protons at high temperatures can be schematically represented by a set of the following reactions:

Fe + H2O → FeO + H2

2 Fe + 3 H2O → Fe2O3 + 3 H2

3 Fe + 4 H2O → Fe3O4 + 4 H2

Many metals, such as zirconium, undergo a similar reaction with water to produce hydrogen. Hydrogen was liquefied for the first time by James Dewar in 1898 using regenerative refrigeration and his invention, the vacuum flask. IN next year it produced solid hydrogen. Deuterium was discovered in December 1931 by Harold Urey, and tritium was prepared in 1934 by Ernest Rutherford, Mark Oliphant, and Paul Harteck. Heavy water, which consists of deuterium instead of ordinary hydrogen, was discovered by Urey's group in 1932. François Isaac de Rivaz built the first Rivaz engine, the engine internal combustion, propelled by hydrogen and oxygen, in 1806. Edward Daniel Clark invented the hydrogen gas tube in 1819. The Döbereiner flint (the first full-fledged lighter) was invented in 1823. The first hydrogen balloon was invented by Jacques Charles in 1783. Hydrogen provided the rise of the first reliable form air traffic after the invention of the first hydrogen-propelled airship in 1852 by Henri Giffard. The German Count Ferdinand von Zeppelin promoted the idea of ​​rigid airships propelled into the air by hydrogen, which were later called Zeppelins; the first of these first flew in 1900. Regularly scheduled flights began in 1910 and by the outbreak of the First World War in August 1914 they carried 35,000 passengers without major incident. During the war, hydrogen airships were used as observation platforms and bombers. The first non-stop transatlantic flight was made by the British airship R34 in 1919. Regular passenger service resumed in the 1920s, and the discovery of helium reserves in the United States was expected to improve travel safety, but the US government refused to sell the gas for this purpose, so H2 was used in the Hindenburg airship, which was destroyed in a fire in Milan in New York. -Jersey May 6, 1937. The incident was broadcast live on radio and filmed. It was widely assumed that the cause of the ignition was a hydrogen leak, but subsequent studies indicate that the aluminized fabric covering was ignited by static electricity. But by this time, hydrogen's reputation as a lifting gas was already damaged. That same year, the first hydrogen-cooled turbogenerator, with hydrogen gas as a coolant in the rotor and stator, entered service in 1937 in Dayton, Ohio, by Dayton Power & Light Co.; Due to the thermal conductivity of hydrogen gas, it is the most common gas for use in this field today. The nickel-hydrogen battery was first used in 1977 on board the US Navigation Technology Satellite-2 (NTS-2). The ISS, Mars Odyssey and Mars Global Surveyor are equipped with nickel-hydrogen batteries. In the dark portion of its orbit, the Hubble Space Telescope is also powered by nickel-hydrogen batteries, which were finally replaced in May 2009, more than 19 years after launch and 13 years after they were designed.

Role in quantum theory

Due to its simple atomic structure consisting of only a proton and an electron, the hydrogen atom, along with the spectrum of light created from or absorbed by it, was central to the development of the theory of atomic structure. In addition, the study of the corresponding simplicity of the hydrogen molecule and the corresponding H+2 cation led to an understanding of the nature of the chemical bond, which was quickly followed by the physical treatment of the hydrogen atom in quantum mechanics in mid-2020. One of the first quantum effects that were clearly observed (but not understood at the time) was Maxwell's observation involving hydrogen half a century before the full quantum mechanical theory appeared. Maxwell noted that specific heat H2 irreversibly leaves the diatomic gas below room temperature and begins to increasingly resemble the specific heat of the monatomic gas at cryogenic temperatures. According to quantum theory, this behavior arises from the spacing of the (quantized) rotational energy levels, which are particularly widely spaced in H2 due to its low mass. These widely spaced levels prevent thermal energy from being equally divided into rotational motion in hydrogen at low temperatures. Diatom gases, which are made of heavier atoms, do not have such widely spaced levels and do not exhibit the same effect. Antihydrogen is the antimaterial analogue of hydrogen. It consists of an antiproton with a positron. Antihydrogen is the only type of antimatter atom that has been produced as of 2015.

Being in nature

Hydrogen is the most abundant chemical element in the universe, making up 75% of normal matter by mass and more than 90% by number of atoms. (Most of the mass of the universe, however, is not in the form of this chemical element, but is thought to have as yet undetected forms of mass such as dark matter and dark energy.) This element is found in great abundance in stars and gas giants. H2 molecular clouds are associated with star formation. Hydrogen plays a vital role in the powering of stars through the proton-proton reaction and nuclear fusion of the CNO cycle. Throughout the world, hydrogen occurs primarily in atomic and plasma states with properties completely different from those of molecular hydrogen. As a plasma, the electron and proton of hydrogen are not bound to each other, resulting in very high electrical conductivity and high emissivity (producing light from the Sun and other stars). Charged particles are strongly influenced by magnetic and electric fields. For example, in the solar wind they interact with the Earth's magnetosphere, creating Birkeland currents and Polar Lights. Hydrogen is in neutral atomic state in the interstellar medium. The large amounts of neutral hydrogen found in decaying Lyman-alpha systems are thought to dominate the cosmological baryon density of the Universe up to redshift z = 4. Under normal conditions on Earth, elemental hydrogen exists as a diatomic gas, H2. However, hydrogen gas is very rare in the Earth's atmosphere (1 ppm by volume) due to its light weight, which allows it to overcome Earth's gravity more easily than more heavy gases. However, hydrogen is the third most abundant element on the Earth's surface, existing primarily in the form chemical compounds, such as hydrocarbons and water. Hydrogen gas is produced by some bacteria and algae and is a natural component of flute, as is methane, which is an increasingly important source of hydrogen. A molecular form called protonated molecular hydrogen (H+3) is found in the interstellar medium, where it is generated by the ionization of molecular hydrogen from cosmic rays. This charged ion has also been observed in the upper atmosphere of the planet Jupiter. The ion is relatively stable in the environment due to its low temperature and density. H+3 is one of the most abundant ions in the Universe and plays a significant role in the chemistry of the interstellar medium. Neutral triatomic hydrogen H3 can only exist in an excited form and is unstable. On the contrary, positive molecular ion Hydrogen (H+2) is a rare molecule in the Universe.

Hydrogen production

H2 is produced in chemical and biological laboratories, often as a byproduct of other reactions; in industry for the hydrogenation of unsaturated substrates; and in nature as a means of displacing reducing equivalents in biochemical reactions.

Steam reforming

Hydrogen can be produced in several ways, but economically the most important processes involve removing hydrogen from hydrocarbons, as about 95% of hydrogen production in 2000 came from steam reforming. Commercially, large volumes of hydrogen are usually produced by steam reforming of natural gas. At high temperatures (1000-1400 K, 700-1100 °C or 1300-2000 °F), steam (water vapor) reacts with methane to produce carbon monoxide and H2.

CH4 + H2O → CO + 3 H2

This reaction works best when low pressures, but, nevertheless, it can also be carried out at high pressures (2.0 MPa, 20 atm or 600 inches of mercury). This is because high pressure H2 is the most popular product and pressurized deheating systems work better at higher pressures. The mixture of products is known as "syngas" because it is often used directly to produce methanol and related compounds. Hydrocarbons other than methane can be used to produce synthesis gas with various product ratios. One of the many complications of this highly optimized technology is the formation of coke or carbon:

CH4 → C + 2 H2

Therefore, steam reforming typically uses excess H2O. Additional hydrogen can be recovered from the steam using carbon monoxide through a water gas displacement reaction, especially using an iron oxide catalyst. This reaction is also a common industrial source of carbon dioxide:

CO + H2O → CO2 + H2

Other important methods for H2 include partial oxidation of hydrocarbons:

2 CH4 + O2 → 2 CO + 4 H2

And a coal reaction that can serve as a prelude to the shear reaction described above:

C + H2O → CO + H2

Sometimes hydrogen is produced and consumed in the same industrial process, without separation. In the Haber process for producing ammonia, hydrogen is generated from natural gas. Electrolysis of brine to produce chlorine also produces hydrogen as a by-product.

Metallic acid

In the laboratory, H2 is usually prepared by reacting dilute non-oxidizing acids with certain reactive metals such as zinc with a Kipp apparatus.

Zn + 2 H + → Zn2 + + H2

Aluminum can also produce H2 when treated with bases:

2 Al + 6 H2O + 2 OH- → 2 Al (OH) -4 + 3 H2

Electrolysis of water is a simple way to produce hydrogen. A low voltage current flows through the water and oxygen gas is produced at the anode, while hydrogen gas is produced at the cathode. Typically the cathode is made from platinum or another inert metal when producing hydrogen for storage. If, however, the gas is to be burned in situ, the presence of oxygen is desirable to aid combustion and therefore both electrodes will be made of inert metals. (For example, iron oxidizes and therefore reduces the amount of oxygen produced). Theoretical maximum efficiency(electricity used in relation to energy value hydrogen produced) is in the range of 80-94%.

2 H2O (L) → 2 H2 (g) + O2 (g)

An alloy of aluminum and gallium in the form of granules added to water can be used to produce hydrogen. This process also produces aluminum oxide, but the expensive gallium, which prevents oxide skin from forming on the pellets, can be reused. This has important potential implications for the hydrogen economy, as hydrogen can be produced locally and does not need to be transported.

Thermochemical properties

There are over 200 thermochemical cycles that can be used to separate water, about a dozen of these cycles such as the iron oxide cycle, cerium(IV) oxide cycle, zinc-zinc oxide cycle, sulfur iodine cycle, copper cycle and chlorine and hybrid sulfur cycle are under research and testing to produce hydrogen and oxygen from water and heat without the use of electricity. A number of laboratories (including in France, Germany, Greece, Japan and the USA) are developing thermo chemical methods obtaining hydrogen from solar energy and water.

Anaerobic corrosion

Under anaerobic conditions, iron and steel alloys are slowly oxidized by water protons while being reduced to molecular hydrogen (H2). Anaerobic corrosion of iron leads first to the formation of iron hydroxide (green rust) and can be described by the following reaction: Fe + 2 H2O → Fe (OH) 2 + H2. In turn, under anaerobic conditions, iron hydroxide (Fe (OH) 2) can be oxidized by water protons to form magnetite and molecular hydrogen. This process is described by the Shikorra reaction: 3 Fe (OH) 2 → Fe3O4 + 2 H2O + H2 iron hydroxide → magnesium + water + hydrogen. Well-crystallized magnetite (Fe3O4) is thermodynamically more stable than iron hydroxide (Fe (OH) 2). This process occurs during anaerobic corrosion of iron and steel in anoxic groundwater and during the restoration of soils below the water table.

Geological origin: serpentinization reaction

In the absence of oxygen (O2) in deep geological conditions prevailing far from the Earth's atmosphere, hydrogen (H2) is formed during the process of serpentinization by anaerobic oxidation by water protons (H+) of iron silicate (Fe2+) present in crystal lattice fayalite (Fe2SiO4, olivine-iron end-member). The corresponding reaction leading to the formation of magnetite (Fe3O4), quartz (SiO2) and hydrogen (H2): 3Fe2SiO4 + 2 H2O → 2 Fe3O4 + 3 SiO2 + 3 H2 fayalite + water → magnetite + quartz + hydrogen. This reaction is very similar to the Shikorra reaction observed during the anaerobic oxidation of iron hydroxide in contact with water.

Formation in transformers

Of all dangerous gases generated in power transformers, hydrogen is the most common and is generated in most fault cases; thus, hydrogen production is an early sign serious problems in the life cycle of a transformer.

Applications

Consumption in various processes

Large quantities of H2 are needed in the petroleum and chemical industries. The largest uses of H2 are for the processing (“upgrading”) of fossil fuels and for the production of ammonia. In petrochemical plants, H2 is used in hydrodealkylation, hydrodesulfurization and hydrocracking. H2 has several others important applications. H2 is used as a hydrogenating agent, particularly to increase the saturation levels of unsaturated fats and oils (found in items such as margarine), and in the production of methanol. It is also a source of hydrogen in the production of hydrochloric acid. H2 is also used as a reducing agent for metal ores. Hydrogen is highly soluble in many rare earth and transition metals and is soluble in both nanocrystalline and amorphous metals. The solubility of hydrogen in metals depends on local distortions or impurities in the crystal lattice. This can be useful when hydrogen is purified by passing through hot palladium disks, but the high solubility of the gas is a metallurgical problem that contributes to the embrittlement of many metals, complicating the design of pipelines and storage tanks. In addition to its use as a reagent, H2 has wide applications in physics and technology. It is used as a shielding gas in welding techniques such as atomic hydrogen welding. H2 is used as rotor coolant in electrical generators in power plants because it has the highest thermal conductivity of any gas. Liquid H2 is used in cryogenic research, including superconductivity research. Because H2 is lighter than air, being slightly more than 1/14 the density of air, it was once widely used as a lifting gas in balloons and airships. In newer applications, hydrogen is used in pure form or mixed with nitrogen (sometimes called forming gas) as a tracer gas for instant leak detection. Hydrogen is used in the automotive, chemical, energy, aerospace and telecommunications industries. Hydrogen is an approved food additive (E 949) that allows leak testing of foods, among other antioxidant properties. Rare isotopes of hydrogen also have specific uses. Deuterium (hydrogen-2) is used in nuclear fission applications as a slow neutron moderator and in nuclear fusion reactions. Deuterium compounds are used in the fields of chemistry and biology to study the isotope effects of reactions. Tritium (hydrogen-3) produced in nuclear reactors, is used in the production of hydrogen bombs, as an isotope tracer in the biological sciences, and as a radiation source in luminous paints. The triple point temperature of equilibrium hydrogen is the defining fixed point on the ITS-90 temperature scale at 13.8033 kelvin.

Cooling medium

Hydrogen is commonly used in power plants as a coolant in generators due to a number of favorable properties that are a direct result of its light diatomic molecules. These include low density, low viscosity, and the highest specific heat capacity and thermal conductivity of any gas.

Energy carrier

Hydrogen is not an energy resource, except in the hypothetical context of commercial fusion power plants using deuterium or tritium, a technology that is currently far from mature. The sun's energy comes from nuclear fusion of hydrogen, but this process is difficult to achieve on Earth. Elemental hydrogen from solar, biological or electrical sources requires more energy to produce it than is consumed when burning it, so in these cases hydrogen functions as an energy carrier, similar to a battery. Hydrogen can be produced from fossil sources (such as methane), but these sources are exhaustible. The energy density per unit volume of both liquid hydrogen and compressed gaseous hydrogen at any practically achievable pressure is significantly less than that of traditional sources energy, although the energy density per unit mass of fuel is higher. However, elemental hydrogen has been widely discussed in the energy context as a possible future economy-wide energy carrier. For example, CO2 sequestration followed by carbon capture and storage can be carried out at the point of H2 production from fossil fuels. Hydrogen used in transport will burn relatively cleanly, with some NOx emissions but no carbon emissions. However, the infrastructure costs associated with a full conversion to a hydrogen economy will be significant. Fuel cells can convert hydrogen and oxygen directly into electricity more efficiently than internal combustion engines.

Semiconductor industry

Hydrogen is used to saturate the dangling bonds of amorphous silicon and amorphous carbon, which helps stabilize the properties of the material. It is also a potential electron donor in various oxide materials, including ZnO, SnO2, CdO, MgO, ZrO2, HfO2, La2O3, Y2O3, TiO2, SrTiO3, LaAlO3, SiO2, Al2O3, ZrSiO4, HfSiO4 and SrZrO3.

Biological reactions

H2 is a product of some anaerobic metabolism and is produced by several microorganisms, usually through reactions catalyzed by iron- or nickel-containing enzymes called hydrogenases. These enzymes catalyze a reversible redox reaction between H2 and its components - two protons and two electrons. The creation of hydrogen gas occurs by transferring the reducing equivalents produced by the fermentation of pyruvate into water. The natural cycle of hydrogen production and consumption by organisms is called the hydrogen cycle. Water splitting, the process by which water is broken down into its constituent protons, electrons and oxygen, occurs in light reactions in all photosynthetic organisms. Some such organisms, including the algae Chlamydomonas Reinhardtii and cyanobacteria, have evolved a second stage in dark reactions in which protons and electrons are reduced to form H2 gas by specialized hydrogenases in the chloroplast. Attempts have been made to genetically modify cyanobacterial hydrases to efficiently synthesize H2 gas even in the presence of oxygen. Efforts have also been made using genetically modified algae in a bioreactor.

It has its own specific position in the periodic table, which reflects the properties it exhibits and speaks about its electronic structure. However, among all of them there is one special atom that occupies two cells at once. It is located in two groups of elements that are completely opposite in their properties. This is hydrogen. Such features make it unique.

Hydrogen is not just an element, but also a simple substance, as well as component many complex compounds, biogenic and organogenic element. Therefore, let us consider its characteristics and properties in more detail.

Hydrogen as a chemical element

Hydrogen is an element of the first group of the main subgroup, as well as the seventh group of the main subgroup in the first minor period. This period consists of only two atoms: helium and the element we are considering. Let us describe the main features of the position of hydrogen in the periodic table.

1. The atomic number of hydrogen is 1, the number of electrons is the same, and, accordingly, the number of protons is the same. Atomic mass - 1.00795. There are three isotopes of this element with mass numbers 1, 2, 3. However, the properties of each of them are very different, since an increase in mass even by one for hydrogen is immediately double.
2. The fact that it contains only one electron on its outer surface allows it to successfully exhibit both oxidative and restorative properties. In addition, after donating an electron, it remains with a free orbital, which takes part in the formation chemical bonds according to the donor-acceptor mechanism.
3. Hydrogen is a strong reducing agent. Therefore, its main place is considered to be the first group of the main subgroup, where it heads the most active metals - alkali.
4. However, when interacting with strong reducing agents, such as metals, it can also be an oxidizing agent, accepting an electron. These compounds are called hydrides. According to this feature, it heads the subgroup of halogens with which it is similar.
5. Due to its very small atomic mass, hydrogen is considered the lightest element. In addition, its density is also very low, so it is also a benchmark for lightness.

Thus, it is obvious that the hydrogen atom is a completely unique element, unlike all other elements. Consequently, its properties are also special, and the simple and complex substances formed are very important. Let's consider them further.

Simple substance

If we talk about this element as a molecule, then we must say that it is diatomic. That is, hydrogen (a simple substance) is a gas. Its empirical formula will be written as H2, and its graphical formula will be written through a single sigma H-H relationship. The mechanism of bond formation between atoms is covalent nonpolar.

1. Steam methane reforming.
2. Coal gasification - the process involves heating coal to 1000 0 C, resulting in the formation of hydrogen and high-carbon coal.
3. Electrolysis. This method can only be used for aqueous solutions of various salts, since the melts do not lead to a discharge of water at the cathode.

Laboratory methods for producing hydrogen:

1. Hydrolysis of metal hydrides.
2. The effect of dilute acids on active metals and medium activity.
3. Interaction between alkaline and alkaline earth metals with water.

To collect the hydrogen produced, you must hold the test tube upside down. After all, this gas cannot be collected in the same way as, for example, carbon dioxide. This is hydrogen, it is much lighter than air. It evaporates quickly, and large quantities Explodes when mixed with air. Therefore, the test tube should be inverted. After filling it, it must be closed with a rubber stopper.

To check the purity of the collected hydrogen, you should bring a lit match to the neck. If the clap is dull and quiet, it means the gas is clean, with minimal air impurities. If it is loud and whistling, it is dirty, with a large proportion of foreign components.

Areas of use

When hydrogen is burned, such a large amount of energy (heat) is released that this gas is considered the most profitable fuel. Moreover, it is environmentally friendly. However, to date its application in this area is limited. This is due to ill-conceived and unsolved problems of synthesizing pure hydrogen, which would be suitable for use as fuel in reactors, engines and portable devices, as well as residential heating boilers.

After all, the methods for producing this gas are quite expensive, so first it is necessary to develop a special synthesis method. One that will allow you to obtain the product in large volume and at minimal cost.

There are several main areas in which the gas we are considering is used.

1. Chemical syntheses. Hydrogenation is used to produce soaps, margarines, and plastics. With the participation of hydrogen, methanol and ammonia, as well as other compounds, are synthesized.
2. In the food industry - as additive E949.
3. Aviation industry (rocket science, aircraft manufacturing).
4. Electric power industry.
5. Meteorology.
6. Environmentally friendly fuel.

Obviously, hydrogen is as important as it is abundant in nature. The various compounds it forms play an even greater role.

Hydrogen compounds

These are complex substances containing hydrogen atoms. There are several main types of such substances.

1. Hydrogen halides. General formula- HHal. Of particular importance among them is hydrogen chloride. It is a gas that dissolves in water to form a solution of hydrochloric acid. This acid is widely used in almost all chemical syntheses. Moreover, both organic and inorganic. Hydrogen chloride is a compound with the empirical formula HCL and is one of the largest produced in our country annually. Hydrogen halides also include hydrogen iodide, hydrogen fluoride and hydrogen bromide. They all form the corresponding acids.
2. Volatile Almost all of them are quite poisonous gases. For example, hydrogen sulfide, methane, silane, phosphine and others. At the same time, they are very flammable.
3. Hydrides are compounds with metals. They belong to the class of salts.
4. Hydroxides: bases, acids and amphoteric compounds. They necessarily contain hydrogen atoms, one or more. Example: NaOH, K 2, H 2 SO 4 and others.
5. Hydrogen hydroxide. This compound is better known as water. Another name is hydrogen oxide. The empirical formula looks like this - H 2 O.
6. Hydrogen peroxide. This is a strong oxidizing agent, the formula of which is H 2 O 2.
7. Numerous organic compounds: hydrocarbons, proteins, fats, lipids, vitamins, hormones, essential oils and others.

It is obvious that the variety of compounds of the element we are considering is very large. This once again confirms it high value for nature and humans, as well as for all living beings.

- this is the best solvent

As mentioned above, the common name of this substance- water. Consists of two hydrogen atoms and one oxygen, connected by covalent polar bonds. The water molecule is a dipole, this explains many of the properties it exhibits. In particular, it is a universal solvent.

Exactly at aquatic environment Almost all chemical processes occur. Internal reactions of plastic and energy metabolism in living organisms are also carried out using hydrogen oxide.

Water is rightfully considered the most important substance on the planet. It is known that no living organism can live without it. On Earth it can exist in three states of aggregation:

• liquid;
• gas (steam);
• solid (ice).

Depending on the isotope of hydrogen included in the molecule, three types of water are distinguished.

1. Light or protium. An isotope with mass number 1. Formula - H 2 O. This is the usual form that all organisms use.
2. Deuterium or heavy, its formula is D 2 O. Contains the isotope 2 H.
3. Super heavy or tritium. The formula looks like T 3 O, isotope - 3 H.

The reserves of fresh protium water on the planet are very important. There is already a shortage of it in many countries. Methods are being developed for treating salt water to produce drinking water.

Hydrogen peroxide is a universal remedy

This compound, as mentioned above, is an excellent oxidizing agent. However, with strong representatives he can also behave as a restorer. In addition, it has a pronounced bactericidal effect.

Another name for this compound is peroxide. It is in this form that it is used in medicine. A 3% solution of crystalline hydrate of the compound in question is a medical medicine that is used to treat small wounds for the purpose of disinfecting them. However, it has been proven that this increases the healing time of the wound.

Hydrogen peroxide is also used in rocket fuel, in industry for disinfection and bleaching, and as a foaming agent for the production of appropriate materials (foam, for example). Additionally, peroxide helps clean aquariums, bleach hair, and whiten teeth. However, it causes harm to tissues, so it is not recommended by specialists for these purposes.

Liquid

Hydrogen(lat. Hydrogenium; indicated by the symbol H) is the first element of the periodic table of elements. Widely distributed in nature. The cation (and nucleus) of the most common isotope of hydrogen, 1 H, is the proton. The properties of the 1 H nucleus make it possible to widely use NMR spectroscopy in the analysis of organic substances.

Three isotopes of hydrogen have their own names: 1 H - protium (H), 2 H - deuterium (D) and 3 H - tritium (radioactive) (T).

The simple substance hydrogen - H 2 - is a light colorless gas. When mixed with air or oxygen, it is flammable and explosive. Non-toxic. Soluble in ethanol and a number of metals: iron, nickel, palladium, platinum.

Story

The release of flammable gas during the interaction of acids and metals was observed in the 16th and XVII centuries at the dawn of the formation of chemistry as a science. Mikhail Vasilyevich Lomonosov also directly pointed out its isolation, but he was already definitely aware that it was not phlogiston. The English physicist and chemist Henry Cavendish examined this gas in 1766 and called it “combustible air.” When burned, the “combustible air” produced water, but Cavendish’s adherence to the phlogiston theory prevented him from drawing the correct conclusions. The French chemist Antoine Lavoisier, together with the engineer J. Meunier, using special gasometers, in 1783 carried out the synthesis of water, and then its analysis, decomposing water vapor with hot iron. Thus, he established that “combustible air” is part of water and can be obtained from it.

origin of name

Lavoisier gave hydrogen the name hydrogène - “giving birth to water.” The Russian name “hydrogen” was proposed by the chemist M. F. Soloviev in 1824 - by analogy with Slomonosov’s “oxygen”.

Prevalence

Hydrogen is the most abundant element in the Universe. It accounts for about 92% of all atoms (8% are helium atoms, the share of all other elements combined is less than 0.1%). Thus, hydrogen is the main constituent of stars and interstellar gas. Under conditions of stellar temperatures (for example, the surface temperature of the Sun is ~ 6000 °C), hydrogen exists in the form of plasma; in interstellar space, this element exists in the form of individual molecules, atoms and ions and can form molecular clouds that vary significantly in size, density and temperature.

Earth's crust and living organisms

The mass fraction of hydrogen in the earth's crust is 1% - it is the tenth most abundant element. However, its role in nature is determined not by mass, but by the number of atoms, the share of which among other elements is 17% (second place after oxygen, the share of atoms of which is ~ 52%). Therefore, the value of hydrogen in chemical processes occurring on Earth is almost as great as oxygen. Unlike oxygen, which exists on Earth in both bound and free states, almost all hydrogen on Earth is in the form of compounds; Only a very small amount of hydrogen in the form of a simple substance is contained in the atmosphere (0.00005% by volume).

Hydrogen is part of almost all organic substances and is present in all living cells. In living cells, hydrogen accounts for almost 50% of the number of atoms.

Receipt

Industrial methods for producing simple substances depend on the form in which the corresponding element is found in nature, that is, what can be the raw material for its production. Thus, oxygen available in a free state is obtained physically- separation from liquid air. Hydrogen is almost all in the form of compounds, so chemical methods are used to obtain it. In particular, decomposition reactions can be used. One way to produce hydrogen is through the decomposition of water by electric current.

The main industrial method for producing hydrogen is the reaction of methane, which is part of natural gas, with water. It is carried out at high temperature (it is easy to verify that when passing methane even through boiling water, no reaction occurs):

CH 4 + 2H 2 O = CO 2 + 4H 2 −165 kJ

In the laboratory, to obtain simple substances, they do not necessarily use natural raw materials, but choose those starting materials from which it is easier to isolate the required substance. For example, in the laboratory, oxygen is not obtained from the air. The same applies to the production of hydrogen. One of the laboratory methods for producing hydrogen, which is sometimes used in industry, is the decomposition of water by electric current.

Typically, hydrogen is produced in the laboratory by reacting zinc with hydrochloric acid.

In industry

1.Electrolysis of aqueous salt solutions:

2NaCl + 2H 2 O → H 2 + 2NaOH + Cl 2

2.Passing water vapor over hot coke at a temperature of about 1000 °C:

H2O+C? H2+CO

3. From natural gas.

Steam conversion:

CH 4 + H 2 O ? CO + 3H 2 (1000 °C)

Catalytic oxidation with oxygen:

2CH 4 + O 2 ? 2CO + 4H2

4. Cracking and reforming of hydrocarbons during oil refining.

In the laboratory

1.The effect of dilute acids on metals. To carry out this reaction, zinc and dilute hydrochloric acid are most often used:

Zn + 2HCl → ZnCl 2 + H 2

2.Interaction of calcium with water:

Ca + 2H 2 O → Ca(OH) 2 + H 2

3.Hydrolysis of hydrides:

NaH + H 2 O → NaOH + H 2

4.Effect of alkalis on zinc or aluminum:

2Al + 2NaOH + 6H 2 O → 2Na + 3H 2

Zn + 2KOH + 2H 2 O → K 2 + H 2

5.Using electrolysis. During the electrolysis of aqueous solutions of alkalis or acids, hydrogen is released at the cathode, for example:

2H 3 O + + 2e − → H 2 + 2H 2 O

Physical properties

Hydrogen can exist in two forms (modifications) - in the form of ortho- and para-hydrogen. In an orthohydrogen molecule o-H 2 (mp −259.10 °C, bp −252.56 °C) nuclear spins are directed identically (parallel), and for parahydrogen p-H 2 (melting point −259.32 °C, boiling point −252.89 °C) - opposite to each other (antiparallel). Equilibrium mixture o-H 2 and p-H 2 at a given temperature is called equilibrium hydrogen e-H2.

Hydrogen modifications can be separated by adsorption on active carbon at liquid nitrogen temperature. At very low temperatures, the equilibrium between orthohydrogen and parahydrogen is almost completely shifted towards the latter. At 80 K the ratio of forms is approximately 1:1. When heated, desorbed parahydrogen is converted into orthohydrogen until a mixture is formed that is equilibrium at room temperature (ortho-para: 75:25). Without a catalyst, the transformation occurs slowly (in the conditions of the interstellar medium - with characteristic times up to cosmological), which makes it possible to study the properties of individual modifications.

Hydrogen is the lightest gas, it is 14.5 times lighter than air. Obviously, the smaller the mass of the molecules, the higher their speed at the same temperature. As the lightest molecules, hydrogen molecules move faster than the molecules of any other gas and thus can transfer heat from one body to another faster. It follows that hydrogen has the highest thermal conductivity among gaseous substances. Its thermal conductivity is approximately seven times higher than the thermal conductivity of air.

The hydrogen molecule is diatomic - H2. Under normal conditions, it is a colorless, odorless, and tasteless gas. Density 0.08987 g/l (n.s.), boiling point −252.76 °C, specific heat of combustion 120.9×10 6 J/kg, slightly soluble in water - 18.8 ml/l. Hydrogen is highly soluble in many metals (Ni, Pt, Pd, etc.), especially in palladium (850 volumes per 1 volume of Pd). The solubility of hydrogen in metals is related to its ability to diffuse through them; Diffusion through a carbon alloy (for example, steel) is sometimes accompanied by destruction of the alloy due to the interaction of hydrogen with carbon (so-called decarbonization). Practically insoluble in silver.

Liquid hydrogen exists in a very narrow temperature range from −252.76 to −259.2 °C. It is a colorless liquid, very light (density at −253 °C 0.0708 g/cm3) and fluid (viscosity at −253 °C 13.8 spuaz). The critical parameters of hydrogen are very low: temperature −240.2 °C and pressure 12.8 atm. This explains the difficulties in liquefying hydrogen. IN liquid state equilibrium hydrogen consists of 99.79% para-H2, 0.21% ortho-H2.

Solid hydrogen, melting point −259.2 °C, density 0.0807 g/cm 3 (at −262 °C) - snow-like mass, hexagonal crystals, space group P6/mmc, cell parameters a=3,75 c=6.12. At high pressure, hydrogen transforms into a metallic state.

Isotopes

Hydrogen occurs in the form of three isotopes, which have individual names: 1 H - protium (H), 2 H - deuterium (D), 3 H - tritium (radioactive) (T).

Protium and deuterium are stable isotopes with mass numbers 1 and 2. Their content in nature is 99.9885 ± 0.0070% and 0.0115 ± 0.0070%, respectively. This ratio may vary slightly depending on the source and method of producing hydrogen.

The hydrogen isotope 3H (tritium) is unstable. Its half-life is 12.32 years. Tritium occurs naturally in very small quantities.

The literature also provides data on hydrogen isotopes with mass numbers of 4 - 7 and half-lives of 10 -22 - 10 -23 s.

Natural hydrogen consists of H 2 and HD (deuterium hydrogen) molecules in a ratio of 3200:1. The content of pure deuterium hydrogen D 2 is even less. The ratio of the concentrations of HD and D 2 is approximately 6400:1.

Of all isotopes chemical elements The physical and chemical properties of hydrogen isotopes differ most greatly from each other. This is due to the largest relative change in atomic masses.

	Temperature melting, K	Temperature boiling, K	Triple dot, K/kPa	Critical dot, K/kPa	Density liquid/gas, kg/m³

Deuterium and tritium also have ortho- and para-modifications: p-D 2 , o-D 2 , p-T 2, o-T 2 . Heteroisotope hydrogen (HD, HT, DT) does not have ortho- and para-modifications.

Chemical properties

Fraction of dissociated hydrogen molecules

Hydrogen molecules H2 are quite strong, and in order for hydrogen to react, a lot of energy must be expended:

H 2 = 2H − 432 kJ

Therefore, at ordinary temperatures, hydrogen reacts only with very active metals, for example with calcium, forming calcium hydride:

Ca + H 2 = CaH 2

and with the only non-metal - fluorine, forming hydrogen fluoride:

Hydrogen reacts with most metals and non-metals at elevated temperatures or under other influences, for example, lighting:

O 2 + 2H 2 = 2H 2 O

It can “take away” oxygen from some oxides, for example:

CuO + H 2 = Cu + H 2 O

The written equation reflects the reducing properties of hydrogen.

N 2 + 3H 2 → 2NH 3

Forms hydrogen halides with halogens:

F 2 + H 2 → 2HF, the reaction occurs explosively in the dark and at any temperature,

Cl 2 + H 2 → 2HCl, the reaction proceeds explosively, only in the light.

It interacts with soot under high heat:

C + 2H 2 → CH 4

Interaction with alkali and alkaline earth metals

When interacting with active metals, hydrogen forms hydrides:

2Na + H 2 → 2NaH

Ca + H 2 → CaH 2

Mg + H 2 → MgH 2

Hydrides- salt-like, solid substances, easily hydrolyzed:

CaH 2 + 2H 2 O → Ca(OH) 2 + 2H 2

Interaction with metal oxides (usually d-elements)

Oxides are reduced to metals:

CuO + H 2 → Cu + H 2 O

Fe 2 O 3 + 3H 2 → 2Fe + 3H 2 O

WO 3 + 3H 2 → W + 3H 2 O

Hydrogenation of organic compounds

Molecular hydrogen is widely used in organic synthesis for the reduction of organic compounds. These processes are called hydrogenation reactions. These reactions are carried out in the presence of a catalyst at elevated pressure and temperature. The catalyst can be either homogeneous (eg Wilkinson Catalyst) or heterogeneous (eg Raney nickel, palladium on carbon).

Thus, in particular, during the catalytic hydrogenation of unsaturated compounds such as alkenes and alkynes, saturated compounds are formed - alkanes.

Geochemistry of hydrogen

Free hydrogen H2 is relatively rare in terrestrial gases, but in the form of water it takes an extremely important part in geochemical processes.

Hydrogen can be present in minerals in the form of ammonium ion, hydroxyl ion and crystalline water.

In the atmosphere, hydrogen is continuously produced as a result of the decomposition of water solar radiation. Having a low mass, hydrogen molecules have a high speed of diffusion motion (it is close to the second cosmic speed) and, when they enter the upper layers of the atmosphere, they can fly into outer space.

Features of treatment

Hydrogen, when mixed with air, forms an explosive mixture - the so-called detonating gas. This gas is most explosive when volumetric ratio hydrogen and oxygen 2:1, or hydrogen and air approximately 2:5, since air contains approximately 21% oxygen. Hydrogen is also a fire hazard. Liquid hydrogen can cause severe frostbite if it comes into contact with the skin.

Explosive concentrations of hydrogen and oxygen occur from 4% to 96% by volume. When mixed with air from 4% to 75(74)% by volume.

Economy

The cost of hydrogen for large wholesale supplies ranges from $2-5 per kg.

Application

Atomic hydrogen is used for atomic hydrogen welding.

Chemical industry

• In the production of ammonia, methanol, soap and plastics
• In the production of margarine from liquid vegetable oils
• Registered as a dietary supplement E949(packaging gas)

Food industry

Aviation industry

Hydrogen is very light and always rises in the air. Once upon a time, airships and Balloons filled with hydrogen. But in the 30s. XX century There were several disasters during which airships exploded and burned. Nowadays, airships are filled with helium, despite its significantly higher cost.

Fuel

Hydrogen is used as rocket fuel.

Research is underway on the use of hydrogen as a fuel for cars and trucks. Hydrogen engines do not pollute the environment and emit only water vapor.

Hydrogen-oxygen fuel cells use hydrogen to directly convert the energy of a chemical reaction into electrical energy.

"Liquid Hydrogen"(“LH”) is the liquid state of hydrogen, with a low specific density of 0.07 g/cm³ and cryogenic properties with a freezing point of 14.01 K (−259.14 °C) and a boiling point of 20.28 K (−252.87 °C). It is a colorless, odorless liquid, which when mixed with air is classified as explosive with a flammability range of 4-75%. The spin ratio of isomers in liquid hydrogen is: 99.79% - parahydrogen; 0.21% - orthohydrogen. The expansion coefficient of hydrogen when changing its state of aggregation to gaseous is 848:1 at 20°C.

As with any other gas, liquefaction of hydrogen leads to a decrease in its volume. After liquefaction, liquid liquid is stored in thermally insulated containers under pressure. Liquid hydrogen Liquid hydrogen, LH2, LH 2) is actively used in industry, as a form of gas storage, and in the space industry, as rocket fuel.

Story

The first documented use of artificial refrigeration was carried out by the English scientist William Cullen in 1756, Gaspard Monge was the first to obtain a liquid state of sulfur oxide in 1784, Michael Faraday was the first to obtain liquefied ammonia, the American inventor Oliver Evans was the first to develop a refrigeration compressor in 1805, Jacob Perkins was the first to patent cooling machine in 1834 and John Gorey was the first to patent an air conditioner in the United States in 1851. Werner Siemens proposed the concept of regenerative cooling in 1857, Karl Linde patented equipment for producing liquid air using a cascade "Joule-Thomson expansion effect" and regenerative cooling in 1876. In 1885, Polish physicist and chemist Zygmunt Wroblewski published the critical temperature of hydrogen 33 K, the critical pressure 13.3 atm. and boiling point at 23 K. Hydrogen was first liquefied by James Dewar in 1898 using regenerative cooling and his invention, the Dewar flask. The first synthesis of a stable isomer of liquid hydrogen, parahydrogen, was carried out by Paul Harteck and Carl Bonhoeffer in 1929.

Spin isomers of hydrogen

Hydrogen at room temperature consists primarily of a spin isomer, orthohydrogen. After production, liquid hydrogen is in a metastable state and must be converted to the parahydrogen form in order to avoid the explosive exothermic reaction that occurs when it changes at low temperatures. Conversion to the parahydrogen phase is usually accomplished using catalysts such as iron oxide, chromium oxide, activated carbon, platinum-coated asbestos, rare earth metals, or through the use of uranium or nickel additives.

Usage

Liquid hydrogen can be used as a form of fuel storage for internal combustion engines and fuel cells. Various submarines (projects "212A" and "214", Germany) and hydrogen transport concepts have been created using this aggregate form of hydrogen (see for example "DeepC" or "BMW H2R"). Due to the proximity of the designs, the creators of LHV equipment can use or only modify systems using liquefied natural gas (LNG). However, due to the lower bulk density combustion energy requires a larger volume of hydrogen than natural gas. If liquid hydrogen is used instead of "CNG" in piston engines, a more bulky fuel system is usually required. With direct injection, increased losses in the intake tract reduce cylinder filling.

Liquid hydrogen is also used to cool neutrons in neutron scattering experiments. The masses of the neutron and the hydrogen nucleus are almost equal, so the exchange of energy during an elastic collision is most effective.

Advantages

The advantage of using hydrogen is the “zero emissions” of its use. The product of its interaction with air is water.

Obstacles

One liter of “ZhV” weighs only 0.07 kg. That is, its specific gravity is 70.99 g/l at 20 K. Liquid hydrogen requires cryogenic storage technology, such as special thermally insulated containers and requires special handling, which is typical for all cryogenic materials. It is close in this regard to liquid oxygen, but requires greater caution due to the fire hazard. Even with insulated containers, it is difficult to keep it at the low temperatures required to keep it liquid (it typically evaporates at a rate of 1% per day). When handling it, you also need to follow the usual safety precautions when working with hydrogen - it is cold enough to liquefy air, which is explosive.

Rocket fuel

Liquid hydrogen is a common component of rocket fuels, which is used to propel launch vehicles and spacecraft. In most liquid hydrogen rocket engines, it is first used to regeneratively cool the nozzle and other engine parts before it is mixed with an oxidizer and burned to produce thrust. Modern engines using H 2 /O 2 components consume a fuel mixture over-enriched in hydrogen, which leads to a certain amount of unburned hydrogen in the exhaust. In addition to increasing the specific impulse of the engine by reducing molecular weight, this also reduces erosion of the nozzle and combustion chamber.

Such obstacles to the use of LH in other areas, such as cryogenic nature and low density, are also a limiting factor for use in this case. As of 2009, there is only one launch vehicle (Delta-4 launch vehicle), which is entirely a hydrogen rocket. Basically, “ZhV” is used either on the upper stages of rockets or on blocks, which perform a significant part of the work of launching the payload into space in a vacuum. As one of the measures to increase the density of this type of fuel, there are proposals to use sludge-like hydrogen, that is, a semi-frozen form of “liquid hydrogen”.

In the periodic table, hydrogen is located in two groups of elements that are completely opposite in their properties. This feature make it completely unique. Hydrogen is not just an element or substance, but is also an integral part of many complex compounds, organogenic and biogenic element. Therefore, let's look at its properties and characteristics in more detail.

The release of flammable gas during the interaction of metals and acids was observed back in the 16th century, that is, during the formation of chemistry as a science. The famous English scientist Henry Cavendish studied the substance starting in 1766 and gave it the name “combustible air”. When burned, this gas produced water. Unfortunately, the scientist’s adherence to the theory of phlogiston (hypothetical “ultrafine matter”) prevented him from coming to the right conclusions.

The French chemist and naturalist A. Lavoisier, together with the engineer J. Meunier and with the help of special gasometers, synthesized water in 1783, and then analyzed it through the decomposition of water vapor with hot iron. Thus, scientists were able to come to the right conclusions. They found that “combustible air” is not only part of water, but can also be obtained from it.

In 1787, Lavoisier suggested that the gas under study was simple substance and, accordingly, is one of the primary chemical elements. He called it hydrogene (from the Greek words hydor - water + gennao - I give birth), i.e. “giving birth to water.”

The Russian name “hydrogen” was proposed in 1824 by the chemist M. Soloviev. The determination of the composition of water marked the end of the “phlogiston theory.” At the turn of the 18th and 19th centuries, it was found that the hydrogen atom is very light (compared to the atoms of other elements) and its mass was taken as the main unit of comparison atomic masses, receiving a value of 1.

Physical properties

Hydrogen is the lightest substance known to science (it is 14.4 times lighter than air), its density is 0.0899 g/l (1 atm, 0 °C). This material melts (solidifies) and boils (liquefies), respectively, at -259.1 ° C and -252.8 ° C (only helium has lower boiling and melting temperatures).

The critical temperature of hydrogen is extremely low (-240 °C). For this reason, its liquefaction is a rather complex and costly process. The critical pressure of the substance is 12.8 kgf/cm², and the critical density is 0.0312 g/cm³. Among all gases, hydrogen has the highest thermal conductivity: at 1 atm and 0 °C it is equal to 0.174 W/(mxK).

The specific heat capacity of the substance under the same conditions is 14.208 kJ/(kgxK) or 3.394 cal/(rx°C). This element is slightly soluble in water (about 0.0182 ml/g at 1 atm and 20 °C), but well soluble in most metals (Ni, Pt, Pa and others), especially in palladium (about 850 volumes per volume of Pd ).

The latter property is associated with its ability to diffuse, and diffusion through a carbon alloy (for example, steel) can be accompanied by the destruction of the alloy due to the interaction of hydrogen with carbon (this process is called decarbonization). In the liquid state, the substance is very light (density - 0.0708 g/cm³ at t° = -253 °C) and fluid (viscosity - 13.8 spoise under the same conditions).

In many compounds, this element exhibits a +1 valency (oxidation state), like sodium and other alkali metals. It is usually considered as an analogue of these metals. Accordingly, he heads group I of the periodic system. In metal hydrides, the hydrogen ion exhibits a negative charge (the oxidation state is -1), that is, Na+H- has a structure similar to Na+Cl- chloride. In accordance with this and some other facts (proximity physical properties element “H” and halogens, the ability to replace it with halogens in organic compounds) Hydrogene belongs to group VII of the periodic system.

Under normal conditions, molecular hydrogen has low activity, directly combining only with the most active of non-metals (with fluorine and chlorine, with the latter - in the light). In turn, when heated, it interacts with many chemical elements.

Atomic hydrogen has increased chemical activity (compared to molecular hydrogen). With oxygen it forms water according to the formula:

Н₂ + ½О₂ = Н₂О,

releasing 285.937 kJ/mol of heat or 68.3174 kcal/mol (25 °C, 1 atm). Under normal temperature conditions, the reaction proceeds rather slowly, and at t° >= 550 °C it is uncontrollable. The explosive limits of a hydrogen + oxygen mixture by volume are 4–94% H₂, and a hydrogen + air mixture is 4–74% H₂ (a mixture of two volumes of H₂ and one volume of O₂ is called detonating gas).

This element is used to reduce most metals, as it removes oxygen from oxides:

Fe₃O₄ + 4H₂ = 3Fe + 4H₂O,

CuO + H₂ = Cu + H₂O, etc.

Hydrogen forms hydrogen halides with different halogens, for example:

H₂ + Cl₂ = 2HCl.

However, when reacting with fluorine, hydrogen explodes (this also happens in the dark, at -252 ° C), with bromine and chlorine it reacts only when heated or illuminated, and with iodine - only when heated. When interacting with nitrogen, ammonia is formed, but only on the catalyst, when high blood pressure and temperature:

ЗН₂ + N₂ = 2NN₃.

When heated, hydrogen reacts actively with sulfur:

H₂ + S = H₂S (hydrogen sulfide),

and much more difficult with tellurium or selenium. Hydrogen reacts with pure carbon without a catalyst, but at high temperatures:

2H₂ + C (amorphous) = CH₄ (methane).

This substance reacts directly with some of the metals (alkali, alkaline earth and others), forming hydrides, for example:

H₂ + 2Li = 2LiH.

Important practical significance have interactions between hydrogen and carbon(II) monoxide. In this case, depending on the pressure, temperature and catalyst, different organic compounds are formed: HCHO, CH₃OH, etc. Unsaturated hydrocarbons during the reaction become saturated, for example:

С n Н₂ n + Н₂ = С n Н₂ n ₊₂.

Hydrogen and its compounds play an exceptional role in chemistry. It determines the acidic properties of the so-called. protic acids, tends to form with different elements hydrogen bonding, which has a significant impact on the properties of many inorganic and organic compounds.

Hydrogen production

The main types of raw materials for industrial production This element includes oil refining gases, natural combustible and coke oven gases. It is also obtained from water through electrolysis (in places where electricity is available). One of the most important methods for producing material from natural gas is the catalytic interaction of hydrocarbons, mainly methane, with water vapor (so-called conversion). For example:

CH₄ + H₂O = CO + ZN₂.

Incomplete oxidation of hydrocarbons with oxygen:

CH₄ + ½O₂ = CO + 2H₂.

The synthesized carbon monoxide (II) undergoes conversion:

CO + H₂O = CO₂ + H₂.

Hydrogen produced from natural gas is the cheapest.

For the electrolysis of water, direct current is used, which is passed through a solution of NaOH or KOH (acids are not used to avoid corrosion of the equipment). In laboratory conditions, the material is obtained by electrolysis of water or as a result of the reaction between hydrochloric acid and zinc. However, ready-made factory material in cylinders is more often used.

From oil refining gases and coke oven gas this element isolated by removing all other components of the gas mixture, since they liquefy more easily during deep cooling.

This material began to be produced industrially at the end of the 18th century. Then it was used for filling balloons. At the moment, hydrogen is widely used in industry, mainly in the chemical industry, for the production of ammonia.

Mass consumers of the substance are producers of methyl and other alcohols, synthetic gasoline and many other products. They are obtained by synthesis from carbon monoxide (II) and hydrogen. Hydrogene is used for the hydrogenation of heavy and solid liquid fuels, fats, etc., for the synthesis of HCl, hydrotreating of petroleum products, as well as in metal cutting/welding. The most important elements for nuclear energy are its isotopes - tritium and deuterium.

Biological role of hydrogen

About 10% of the mass of living organisms (on average) comes from this element. It is part of water and the most important groups of natural compounds, including proteins, nucleic acids, lipids, and carbohydrates. What is it used for?

This material plays a decisive role: in maintaining the spatial structure of proteins (quaternary), in implementing the principle of complementarity of nucleic acids (i.e., in the implementation and storage of genetic information), and in general in “recognition” at the molecular level.

The hydrogen ion H+ takes part in important dynamic reactions/processes in the body. Including: in biological oxidation, which provides living cells with energy, in biosynthesis reactions, in photosynthesis in plants, in bacterial photosynthesis and nitrogen fixation, in maintaining acid-base balance and homeostasis, in membrane transport processes. Along with carbon and oxygen, it forms the functional and structural basis of life phenomena.