Hydrogen is what gas. Hydrogen - what is this substance? Chemical and physical properties of hydrogen

In the periodic system, it has its own specific position, which reflects the properties it exhibits and speaks of its electronic structure. However, among all 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 manifested properties. This is hydrogen. These features make it unique.

Hydrogen is not just an element, but also a simple substance, as well as an integral part of many complex compounds, a biogenic and organogenic element. Therefore, we 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 small 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 system.

1. The serial number of hydrogen is 1, the number of electrons is the same, respectively, the number of protons is the same. The atomic mass is 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 the outer allows it to successfully exhibit both oxidizing and reducing properties. In addition, after the donation of an electron, it remains a free orbital, which takes part in the formation of chemical bonds according to the donor-acceptor mechanism.
3. Hydrogen is a strong reducing agent. Therefore, the first group of the main subgroup is considered to be its main place, where it leads the most active metals - alkali.
4. However, when interacting with strong reducing agents, such as, for example, metals, it can also be an oxidizing agent, accepting an electron. These compounds are called hydrides. On this basis, 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 the benchmark for lightness.

Thus, it is obvious that the hydrogen atom is a completely unique, 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 H 2, and the graphic one - through a single sigma bond H-H. The mechanism of bond formation between atoms is covalent non-polar.

1. Steam reforming of methane.
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 melts do not lead to water discharge at the cathode.

Laboratory methods for producing hydrogen:

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

To collect the resulting hydrogen, it is necessary to keep the test tube turned 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 volatilizes quickly, and explodes when mixed with air in large quantities. Therefore, the tube must 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 cotton is deaf and quiet, then 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. In addition, it is environmentally friendly. However, its use in this area is currently limited. This is due to the 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 obtaining this gas are quite expensive, so first it is necessary to develop a special method of synthesis. One that will allow you to receive 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. Based on hydrogenation, soaps, margarines, and plastics are obtained. With the participation of hydrogen, methanol and ammonia are synthesized, as well as other compounds.
2. In the food industry - as an additive E949.
3. Aviation industry (rocket building, aircraft building).
4. Power industry.
5. Meteorology.
6. Fuel of an environmentally friendly type.

Obviously, hydrogen is as important as it is abundant in nature. An even greater role is played by the various compounds formed by it.

Hydrogen compounds

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

1. Hydrogen halides. The general formula is HHal. Of particular importance among them is hydrogen chloride. It is a gas that dissolves in water to form a hydrochloric acid solution. This acid is widely used in almost all chemical syntheses. And both organic and inorganic. Hydrogen chloride is a compound that has the empirical formula HCL and is one of the largest in terms of annual production in our country. Hydrogen halides also include hydrogen iodide, hydrogen fluoride, and hydrogen bromide. All of them form the corresponding acids.
2. Volatile Almost all of them are quite poisonous gases. For example, hydrogen sulfide, methane, silane, phosphine and others. However, they are very flammable.
3. Hydrides are compounds with metals. They belong to the class of salts.
4. Hydroxides: bases, acids and amphoteric compounds. Their composition necessarily includes 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 for hydrogen oxide. The empirical formula looks like this - H 2 O.
6. Hydrogen peroxide. This is the strongest 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.

Obviously, the variety of compounds of the element we are considering is very large. This once again confirms its high importance for nature and man, as well as for all living beings.

is the best solvent

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

It is in the aquatic environment that almost all chemical processes take place. Internal reactions of plastic and energy metabolism in living organisms are also carried out with the help of hydrogen oxide.

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

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

Depending on the isotope of hydrogen that is part of the molecule, there are three types of water.

1. Light or protium. An isotope with a mass number of 1. The formula is 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, the isotope is 3 H.

The reserves of fresh protium water on the planet are very important. It is already lacking in many countries. Methods are being developed to treat salt water in order to obtain drinking water.

Hydrogen peroxide is a universal remedy

This compound, as mentioned above, is an excellent oxidizing agent. However, with strong representatives it can also behave as a reducer. 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 the crystalline hydrate of the compound in question is a medical drug that is used to treat small wounds in order to decontaminate them. However, it has been proven that in this case, wound healing over time increases.

Hydrogen peroxide is also used in rocket fuel, in industry for disinfection and bleaching, as a foaming agent for the production of appropriate materials (foam, for example). In addition, peroxide helps clean aquariums, bleach hair, and whiten teeth. However, at the same time it harms the tissues, therefore it is not recommended by specialists for this purpose.

Hydrogen

HYDROGEN-A; m. A chemical element (H), a light, colorless and odorless gas that combines with oxygen to form water.

◁ Hydrogen, th, th. V connections. V bacteria. V-th bomb(a bomb of enormous destructive power, the explosive effect of which is based on a thermonuclear reaction). Hydrogenous, th, th.

hydrogen

(lat. Hydrogenium), a chemical element of group VII of the periodic system. In nature, there are two stable isotopes (protium and deuterium) and one radioactive isotope (tritium). The molecule is diatomic (H 2). Colorless and odorless gas; density 0.0899 g/l, t kip - 252.76°C. It combines with many elements to form water with oxygen. The most common element in space; makes up (in the form of plasma) more than 70% of the mass of the Sun and stars, the main part of the gases of the interstellar medium and nebulae. The hydrogen atom is part of many acids and bases, most organic compounds. They are used in the production of ammonia, hydrochloric acid, for the hydrogenation of fats, etc., in welding and cutting metals. Promising as a fuel (see. Hydrogen energy).

HYDROGEN

HYDROGEN (lat. Hydrogenium), H, a chemical element with atomic number 1, atomic mass 1.00794. The chemical symbol for hydrogen, H, is read in our country as "ash", as this letter is pronounced in French.
Natural hydrogen consists of a mixture of two stable nuclides (cm. NUCLIDE) with mass numbers 1.007825 (99.985% in the mixture) and 2.0140 (0.015%). In addition, trace amounts of the radioactive nuclide, tritium, are always present in natural hydrogen. (cm. TRITIUM) 3 H (half-life T 1/2 12.43 years). Since the nucleus of a hydrogen atom contains only 1 proton (there cannot be less protons in the nucleus of an atom), it is sometimes said that hydrogen forms the natural lower boundary of the periodic system of elements of D. I. Mendeleev (although the element hydrogen itself is located in the uppermost part tables). The element hydrogen is located in the first period of the periodic table. It also belongs to the 1st group (group IA of alkali metals (cm. ALKALI METALS)), and to the 7th group (group VIIA of halogens (cm. HALOGENS)).
The masses of atoms in hydrogen isotopes differ greatly (by several times). This leads to noticeable differences in their behavior in physical processes (distillation, electrolysis, etc.) and to certain chemical differences (differences in the behavior of isotopes of one element are called isotope effects; for hydrogen, isotope effects are most significant). Therefore, unlike the isotopes of all other elements, hydrogen isotopes have special symbols and names. Hydrogen with a mass number of 1 is called light hydrogen, or protium (lat. Protium, from the Greek protos - the first), denoted by the symbol H, and its nucleus is called a proton (cm. PROTON (elementary particle)), symbol r. Hydrogen with a mass number of 2 is called heavy hydrogen, deuterium (cm. DEUTERIUM)(Latin Deuterium, from Greek deuteros - the second), the symbols 2 H, or D (read "de") are used to designate it, the nucleus d is the deuteron. A radioactive isotope with a mass number of 3 is called superheavy hydrogen, or tritium (lat. Tritum, from the Greek tritos - the third), the symbol 2 H or T (read "those"), the nucleus t is a triton.
Configuration of a single electron layer of a neutral unexcited hydrogen atom 1 s 1 . In compounds, it exhibits oxidation states +1 and, less often, -1 (valency I). The radius of the neutral hydrogen atom is 0.024 nm. The ionization energy of the atom is 13.595 eV, the electron affinity is 0.75 eV. On the Pauling scale, the electronegativity of hydrogen is 2.20. Hydrogen is one of the non-metals.
In its free form, it is a light, flammable gas without color, odor or taste.
Discovery history
The release of combustible gas during the interaction of acids and metals was observed in the 16th and 17th centuries at the dawn of the formation of chemistry as a science. The famous English physicist and chemist G. Cavendish (cm. Cavendish Henry) in 1766 he investigated this gas and called it "combustible air". When burned, "combustible air" gave water, but Cavendish's adherence to the theory of phlogiston (cm. PHLOGISTON) prevented him from drawing correct conclusions. French chemist A. Lavoisier (cm. Lavoisier Antoine Laurent) together with engineer J. Meunier (cm. MEUNIER Jean-Baptiste Marie Charles), using special gasometers, in 1783 carried out the synthesis of water, and then its analysis, decomposing water vapor with red-hot iron. Thus, he established that "combustible air" is part of the water and can be obtained from it. In 1787, Lavoisier came to the conclusion that "combustible air" is a simple substance, and therefore belongs to the number of chemical elements. He gave it the name hydrogene (from the Greek hydor - water and gennao - give birth) - "giving birth to water." The establishment of the composition of water put an end to the "phlogiston theory". The Russian name "hydrogen" was proposed by the chemist M.F. Solovyov (cm. SOLOVIEV Mikhail Fedorovich) in 1824. 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 the weight (mass) of the hydrogen atom was taken as a unit for comparing the atomic masses of elements. The mass of the hydrogen atom was assigned a value equal to 1.
Being in nature
Hydrogen accounts for about 1% of the mass of the earth's crust (10th place among all elements). Hydrogen is practically never found in its free form on our planet (its traces are found in the upper atmosphere), but it is distributed almost everywhere on Earth in the composition of water. The element hydrogen is a part of organic and inorganic compounds of living organisms, natural gas, oil, coal. It is contained, of course, in the composition of water (about 11% by weight), in various natural crystalline hydrates and minerals, which contain one or more OH hydroxo groups.
Hydrogen as an element dominates the Universe. It accounts for about half the mass of the Sun and other stars, it is present in the atmosphere of a number of planets.
Receipt
Hydrogen can be obtained in many ways. In industry, natural gases are used for this, as well as gases obtained from oil refining, coking and gasification of coal and other fuels. In the production of hydrogen from natural gas (the main component is methane), its catalytic interaction with water vapor and incomplete oxidation with oxygen are carried out:
CH 4 + H 2 O \u003d CO + 3H 2 and CH 4 + 1/2 O 2 \u003d CO 2 + 2H 2
The separation of hydrogen from coke gas and refinery gases is based on their liquefaction during deep cooling and removal from the mixture of gases that are more easily liquefied than hydrogen. In the presence of cheap electricity, hydrogen is obtained by electrolysis of water, passing current through alkali solutions. Under laboratory conditions, hydrogen is easily obtained by the interaction of metals with acids, for example, zinc with hydrochloric acid.
Physical and Chemical properties
Under normal conditions, hydrogen is a light (density under normal conditions 0.0899 kg / m 3) colorless gas. Melting point -259.15 °C, boiling point -252.7 °C. Liquid hydrogen (at the boiling point) has a density of 70.8 kg/m 3 and is the lightest liquid. The standard electrode potential H 2 / H - in an aqueous solution is taken equal to 0. Hydrogen is poorly soluble in water: at 0 ° C, the solubility is less than 0.02 cm 3 / ml, but it is highly soluble in some metals (sponge iron and others), especially good - in metallic palladium (about 850 volumes of hydrogen in 1 volume of metal). The heat of combustion of hydrogen is 143.06 MJ/kg.
Exists in the form of diatomic H 2 molecules. The dissociation constant of H 2 into atoms at 300 K is 2.56 10 -34. The dissociation energy of the H 2 molecule into atoms is 436 kJ/mol. The internuclear distance in the H 2 molecule is 0.07414 nm.
Since the nucleus of each H atom, which is part of the molecule, has its own spin (cm. SPIN), then molecular hydrogen can be in two forms: in the form of orthohydrogen (o-H 2) (both spins have the same orientation) and in the form of parahydrogen (p-H 2) (spins have different orientations). Under normal conditions, normal hydrogen is a mixture of 75% o-H 2 and 25% p-H 2 . The physical properties of p- and o-H 2 differ slightly from each other. Thus, if the boiling point pure o-n 2 20.45 K, then pure p-n 2 - 20.26 K. The transformation of o-H 2 into p-H 2 is accompanied by the release of 1418 J / mol of heat.
It has been repeatedly argued in the scientific literature that high pressures(above 10 GPa) and at low temperatures (about 10 K and below), solid hydrogen, which usually crystallizes in a hexagonal molecular-type lattice, can transform into a substance with metallic properties, possibly even a superconductor. However, there is still no unambiguous data on the possibility of such a transition.
High strength chemical bond between atoms in an H 2 molecule (which, for example, using the method of molecular orbitals, can be explained by the fact that in this molecule the electron pair is in the bonding orbital, and the loosening orbital is not populated with electrons) leads to the fact that at room temperature, gaseous hydrogen is chemically inactive . So, without heating, with simple mixing, hydrogen reacts (with an explosion) only with gaseous fluorine:
H 2 + F 2 \u003d 2HF + Q.
If a mixture of hydrogen and chlorine at room temperature is irradiated with ultraviolet light, then an immediate formation of hydrogen chloride HCl is observed. The reaction of hydrogen with oxygen occurs with an explosion if a catalyst, metallic palladium (or platinum), is introduced into the mixture of these gases. When ignited, a mixture of hydrogen and oxygen (the so-called explosive gas (cm. EXPLOSIVE GAS)) explodes, and an explosion can occur in mixtures in which the hydrogen content is from 5 to 95 volume percent. Pure hydrogen in air or in pure oxygen burns quietly with the release of a large amount of heat:
H 2 + 1 / 2O 2 \u003d H 2 O + 285.75 kJ / mol
If hydrogen interacts with other non-metals and metals, then only under certain conditions (heating, high pressure, the presence of a catalyst). Thus, hydrogen reacts reversibly with nitrogen at high blood pressure(20-30 MPa and more) and at a temperature of 300-400 ° C in the presence of a catalyst - iron:
3H 2 + N 2 = 2NH 3 + Q.
Also, only when heated, hydrogen reacts with sulfur to form hydrogen sulfide H 2 S, with bromine - to form hydrogen bromide HBr, with iodine - to form hydrogen iodide HI. Hydrogen reacts with coal (graphite) to form a mixture of hydrocarbons of various compositions. Hydrogen does not interact directly with boron, silicon, and phosphorus; compounds of these elements with hydrogen are obtained indirectly.
When heated, hydrogen is able to react with alkali, alkaline earth metals and magnesium to form compounds with an ionic bond character, which contain hydrogen in the oxidation state –1. So, when calcium is heated in a hydrogen atmosphere, a salt-like hydride of the composition CaH 2 is formed. Polymeric aluminum hydride (AlH 3) x - one of the strongest reducing agents - is obtained indirectly (for example, using organoaluminum compounds). With many transition metals (for example, zirconium, hafnium, etc.), hydrogen forms compounds of variable composition (solid solutions).
Hydrogen is able to react not only with many simple, but also with complex substances. First of all, it should be noted the ability of hydrogen to reduce many metals from their oxides (such as iron, nickel, lead, tungsten, copper, etc.). So, when heated to a temperature of 400-450 ° C and above, iron is reduced by hydrogen from any of its oxides, for example:
Fe 2 O 3 + 3H 2 \u003d 2Fe + 3H 2 O.
It should be noted that only metals located in the series of standard potentials beyond manganese can be reduced from oxides by hydrogen. More active metals (including manganese) are not reduced to metal from oxides.
Hydrogen is capable of adding to a double or triple bond to many organic compounds (these are the so-called hydrogenation reactions). For example, in the presence of a nickel catalyst, hydrogenation of ethylene C 2 H 4 can be carried out, and ethane C 2 H 6 is formed:
C 2 H 4 + H 2 \u003d C 2 H 6.
The interaction of carbon monoxide (II) and hydrogen in industry produces methanol:
2H 2 + CO \u003d CH 3 OH.
In compounds in which a hydrogen atom is connected to an atom of a more electronegative element E (E = F, Cl, O, N), hydrogen bonds are formed between the molecules (cm. HYDROGEN BOND)(two E atoms of the same or two different elements are interconnected through the H atom: E "... N ... E"", and all three atoms are located on the same straight line). Such bonds exist between the molecules of water, ammonia , methanol, etc. and lead to a noticeable increase in the boiling points of these substances, an increase in the heat of evaporation, etc.
Application
Hydrogen is used in the synthesis of ammonia NH 3 , hydrogen chloride HCl, methanol CH 3 OH, in the hydrocracking (cracking in a hydrogen atmosphere) of natural hydrocarbons, as a reducing agent in the production of certain metals. hydrogenation (cm. HYDROGENATION) natural vegetable oils get solid fat - margarine. Liquid hydrogen finds use as a rocket fuel and also as a coolant. A mixture of oxygen and hydrogen is used in welding.
At one time, it was suggested that in the near future the main source of energy production would be the reaction of hydrogen combustion, and hydrogen energy would replace traditional sources of energy production (coal, oil, etc.). At the same time, it was assumed that for the production of hydrogen on a large scale it would be possible to use the electrolysis of water. Water electrolysis is a rather energy-intensive process, and it is currently unprofitable to obtain hydrogen by electrolysis on an industrial scale. But it was expected that electrolysis would be based on the use of medium-temperature (500-600 ° C) heat, which occurs in large quantities during the operation of nuclear power plants. This heat is of limited use, and the possibility of obtaining hydrogen with its help would solve both the problem of ecology (when hydrogen is burned in air, the amount of environmentally harmful substances formed is minimal) and the problem of utilization of medium-temperature heat. However, after the Chernobyl disaster, the development nuclear energy coagulates everywhere, so that the specified source of energy becomes unavailable. Therefore, the prospects for the widespread use of hydrogen as an energy source are still shifting at least until the middle of the 21st century.
Features of circulation
Hydrogen is not poisonous, but when handling it, one must constantly take into account its high fire and explosion hazard, and the explosion hazard of hydrogen is increased due to the high ability of the gas to diffuse even through some solid materials. Before starting any heating operations in an atmosphere of hydrogen, you should make sure that it is clean (when igniting hydrogen in a test tube turned upside down, the sound should be dull, not barking).
Biological role
The biological significance of hydrogen is determined by the fact that it is part of water molecules and all the most important groups of natural compounds, including proteins, nucleic acids, lipids, carbohydrates. Approximately 10% of the mass of living organisms is hydrogen. The ability of hydrogen to form a hydrogen bond plays a crucial role in maintaining the spatial quaternary structure of proteins, as well as in implementing the principle of complementarity. (cm. COMPLEMENTARY) in the construction and functions of nucleic acids (that is, in the storage and implementation of genetic information), in general, in the implementation of "recognition" at the molecular level. Hydrogen (H + ion) takes part in the most important dynamic processes and reactions in the body - in biological oxidation, which provides living cells with energy, in photosynthesis in plants, in biosynthesis reactions, in nitrogen fixation and bacterial photosynthesis, in maintaining acid-base balance and homeostasis (cm. homeostasis), in membrane transport processes. Thus, along with oxygen and carbon, hydrogen forms the structural and functional basis of the phenomena of life.

encyclopedic Dictionary. 2009 .

Synonyms:

See what "hydrogen" is in other dictionaries:

Table of nuclides General information Name, symbol Hydrogen 4, 4H Neutrons 3 Protons 1 Nuclide properties Atomic mass 4.027810 (110) ... Wikipedia

Table of nuclides General information Name, symbol Hydrogen 5, 5H Neutrons 4 Protons 1 Nuclide properties Atomic mass 5.035310 (110) ... Wikipedia

Table of nuclides General information Name, symbol Hydrogen 6, 6H Neutrons 5 Protons 1 Nuclide properties Atomic mass 6.044940 (280) ... Wikipedia

Table of nuclides General information Name, symbol Hydrogen 7, 7H Neutrons 6 Protons 1 Nuclide properties Atomic mass 7.052750 (1080) ... Wikipedia

Hydrogen (Hydrogenium) was discovered in the first half of the 16th century by the German physician and naturalist Paracelsus. In 1776, G. Cavendish (England) established its properties and pointed out the differences from other gases. Lavoisier was the first to obtain hydrogen from water and proved that water is a chemical combination of hydrogen and oxygen (1783).

Hydrogen has three isotopes: protium, deuterium or D and tritium or T. Their mass numbers are 1, 2 and 3. Protium and deuterium are stable, tritium is radioactive (half-life 12.5 years). In natural compounds, deuterium and protium are on average contained in a ratio of 1:6800 (according to the number of atoms). Tritium is found in nature in negligible amounts.

The nucleus of a hydrogen atom contains one proton. The nuclei of deuterium and tritium include, in addition to the proton, one and two neutrons, respectively.

The hydrogen molecule consists of two atoms. Here are some properties that characterize the hydrogen atom and molecule:

Atom ionization energy, eV 13.60

Affinity of an atom to an electron, eV 0.75

Relative electronegativity 2.1

Radius of an atom, nm 0.046

Internuclear distance in a molecule, nm 0.0741

Standard ethalpy of dissociation of molecules at 436.1

115. Hydrogen in nature. Obtaining hydrogen.

Hydrogen in the free state is found on Earth only in small quantities. Sometimes it is released along with other gases during volcanic eruptions, as well as from boreholes during oil extraction. But in the form of compounds, hydrogen is very common. This can be seen already from the fact that it makes up a ninth of the mass of water. Hydrogen is a constituent of all plant and animal organisms, oil, hard and brown coal, natural gases, and a number of minerals. The share of hydrogen from the entire mass of the earth's crust, including water and air, accounts for about 1%. However, when recalculated as a percentage of the total number of atoms, the hydrogen content in the earth's crust is 17%.

Hydrogen is the most abundant element in space. It accounts for about half the mass of the Sun and most other stars. It is contained in gaseous nebulae, in interstellar gas, and is part of the stars. In the interior of stars, the nuclei of hydrogen atoms are converted into the nuclei of helium atoms. This process proceeds with the release of energy; for many stars, including the Sun, it serves as the main source of energy. The rate of the process, i.e., the number of hydrogen nuclei that turn into helium nuclei in one cubic meter in one second, is small. Therefore, the amount of energy released per unit time per unit volume is small. However, due to the enormous mass of the Sun, the total amount of energy generated and emitted by the Sun is very large. It corresponds to a decrease in the mass of the Sun by about a second.

In industry, hydrogen is produced mainly from natural gas. This gas, which consists mainly of methane, is mixed with water vapor and oxygen. When a mixture of gases is heated to in the presence of a catalyst, a reaction occurs, which can be schematically represented by the equation:

The resulting mixture of gases is separated. Hydrogen is purified and either used on site or transported in pressurized steel cylinders.

An important industrial method for producing hydrogen is also its isolation from coke oven gas or from petroleum refining gases. It is carried out by deep cooling, in which all gases, except hydrogen, are liquefied.

In laboratories, hydrogen is produced mostly by electrolysis of aqueous solutions. The concentration of these solutions is chosen to match their maximum electrical conductivity. The electrodes are usually made from sheet nickel. This metal does not corrode in alkali solutions, even being an anode. If necessary, the resulting hydrogen is purified from water vapor and traces of oxygen. Of the other laboratory methods, the most common method is the extraction of hydrogen from solutions of sulfuric or hydrochloric acids by the action of zinc on them. The reaction is usually carried out in a Kipp apparatus (Fig. 105).

DEFINITION

Hydrogen is the first element in the Periodic Table. Designation - H from the Latin "hydrogenium". Located in the first period, group IA. Refers to non-metals. The nuclear charge is 1.

Hydrogen is one of the most common chemical elements - its share is about 1% of the mass of all three shells of the earth's crust (atmosphere, hydrosphere and lithosphere), which, when converted to atomic percentages, gives a figure of 17.0.

The main amount of this element is in a bound state. Thus, water contains about 11 wt. %, clay - about 1.5%, etc. In the form of compounds with carbon, hydrogen is part of oil, combustible natural gases and all organisms.

Hydrogen is a colorless and odorless gas (a diagram of the structure of the atom is shown in Fig. 1). Its melting and boiling points are very low (-259 o C and -253 o C, respectively). At a temperature (-240 o C) and under pressure, hydrogen is able to liquefy, and with the rapid evaporation of the resulting liquid, it turns into solid state(transparent crystals). It is slightly soluble in water - 2:100 by volume. Hydrogen is characterized by solubility in some metals, for example, in iron.

Rice. 1. The structure of the hydrogen atom.

Atomic and molecular weight of hydrogen

DEFINITION

Relative atomic mass element is the ratio of the mass of an atom of a given element to 1/12 of the mass of a carbon atom.

The relative atomic mass is dimensionless and is denoted by A r (subscript "r" is the initial letter English word relative, which in translation means "relative"). The relative atomic mass of atomic hydrogen is 1.008 amu.

The masses of molecules, just like the masses of atoms, are expressed in atomic mass units.

DEFINITION

molecular weight substance is called the mass of the molecule, expressed in atomic mass units. Relative molecular weight substances call the ratio of the mass of a molecule of a given substance to 1/12 of the mass of a carbon atom, the mass of which is 12 a.m.u.

It is known that the hydrogen molecule is diatomic - H 2 . The relative molecular weight of a hydrogen molecule will be equal to:

M r (H 2) \u003d 1.008 × 2 \u003d 2.016.

Isotopes of hydrogen

Hydrogen has three isotopes: protium 1 H, deuterium 2 H or D and tritium 3 H or T. Their mass numbers are 1, 2 and 3. Protium and deuterium are stable, tritium is radioactive (half-life 12.5 years). In natural compounds, deuterium and protium are on average contained in a ratio of 1:6800 (according to the number of atoms). Tritium is found in nature in negligible amounts.

The nucleus of the hydrogen atom 1 H contains one proton. The nuclei of deuterium and tritium include, in addition to the proton, one and two neutrons.

Hydrogen ions

A hydrogen atom can either donate its single electron to form a positive ion (which is a "naked" proton), or it can add one electron, turning into a negative ion, which has a helium electronic configuration.

The complete detachment of an electron from a hydrogen atom requires the expenditure of a very large ionization energy:

H + 315 kcal = H + + e.

As a result, in the interaction of hydrogen with metalloids, not ionic, but only polar bonds arise.

The tendency of a neutral atom to attach an excess electron is characterized by the value of its electron affinity. In hydrogen, it is rather weakly expressed (however, this does not mean that such a hydrogen ion cannot exist):

H + e \u003d H - + 19 kcal.

Hydrogen molecule and atom

The hydrogen molecule consists of two atoms - H 2 . Here are some properties that characterize the hydrogen atom and molecule:

Examples of problem solving

EXAMPLE 1

Exercise	Prove that there are hydrides of the general formula EN x containing 12.5% ​​hydrogen.
Solution	Calculate the masses of hydrogen and the unknown element, taking the mass of the sample as 100 g: m(H) = m(EN x)×w(H); m(H) = 100 × 0.125 = 12.5 g. m (E) \u003d m (EN x) - m (H); m (E) \u003d 100 - 12.5 \u003d 87.5 g. Let's find the amount of hydrogen substance and an unknown element, denoting the molar mass of the latter as "x" (the molar mass of hydrogen is 1 g / mol):

Hydrogen is a chemical element with 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 mass of a baryon. Stars are mostly composed of hydrogen in the 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 in the era of recombination. At standard temperatures and pressures, hydrogen is a colorless, odorless, tasteless, non-toxic, non-metallic, flammable diatomic gas with the molecular formula H2. Since hydrogen readily forms covalent bonds with most non-metallic elements, most of the 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., anion) and is known as a hydride, or as a positively charged (i.e., cation) species, denoted by the symbol H+. The hydrogen cation is described as being made up of a simple proton, but the actual 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 energy and binding of its atom) has played a key role in the development of quantum mechanics. Hydrogen gas was first produced artificially in the early 16th century by the reaction of acids with metals. In 1766-81. Henry Cavendish was the first to recognize that hydrogen gas is a discrete substance, and that it produces water when burned, hence its name: hydrogen in Greek means "water producer". The industrial production of hydrogen is mainly associated with the steam conversion of natural gas and, less frequently, with more energy-intensive methods such as water electrolysis. Most hydrogen is used near 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 brittle many metals, making it difficult to design pipelines and storage tanks.

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 spontaneous ignition temperature in air, is 500 °C (932 °F) . Pure hydrogen-oxygen flames emit ultraviolet radiation and with a high oxygen mixture are nearly 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 leak of burning hydrogen; such leaks can be very dangerous. Hydrogen flame under other conditions is blue, and resembles the blue flame of natural gas. The sinking of the airship "Hindenburg" is a notorious example of hydrogen burning, and the case is still under discussion. The visible orange flame in this incident was caused by exposure to a mixture of hydrogen and oxygen combined with carbon compounds from the airship's skin. H2 reacts with every oxidizing element. Hydrogen can spontaneously react at room temperature with chlorine and fluorine to form the corresponding hydrogen halides, hydrogen chloride and hydrogen fluoride, which are also potentially hazardous 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, similar to the Earth's orbit of the Sun. However, the atomic electron and proton are held together by electromagnetic force, while planets and celestial objects are held together by gravity. Due to the discretization of angular momentum postulated in the early quantum mechanics Bohr, the electron in the Bohr model can occupy only 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 that 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 complex processing methods allow you to get small effects special theory relativity and vacuum polarization. In quantum machining, the electron in the ground state hydrogen atom has no torque at all, illustrating how a "planetary orbit" differs from the motion of an electron.

Elementary molecular forms

There are two different spin isomers of diatomic hydrogen molecules that 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 parahydrogen form, 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% of the para form and 75% of the 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 a 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 normal form properties due to differences in rotational heat capacities, which is discussed in more detail in hydrogen spin isomers. The ortho/pair difference also occurs in other hydrogen-containing molecules or functional groups such as water and methylene, but this is of little significance for their thermal properties. The uncatalyzed interconversion between para and ortho H2 increases with increasing temperature; thus, rapidly condensed H2 contains large quantities high energy orthogonal form, which is very slowly converted to the para form. The ortho/para ratio in condensed H2 is an important factor in the preparation and storage of liquid hydrogen: the conversion from ortho to para is exothermic and provides enough heat to vaporize some of the hydrogen liquid, resulting in the 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, the hydrogen takes on a partial positive charge. When bonded to fluorine, oxygen, or nitrogen, hydrogen can participate in the form of a medium-strength non-covalent bond with the hydrogen of other similar molecules, a phenomenon called hydrogen bonding, which is critical to 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 greater variety of compounds with heteroatoms, which, because of their common association with living things, are called organic compounds. The study of their properties is 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 also contain hydrogen, and since it is the carbon-hydrogen bond that gives this class of compounds much 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 by complex synthetic pathways that rarely involve elemental hydrogen.

hydrides

Hydrogen compounds are often called hydrides. The term "hydride" suggests that the H atom has acquired 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 group 1 and 2 salt-containing hydrides, was demonstrated by Moers in 1920 by electrolysis of molten lithium hydride (LiH), producing a stoichiometric amount of hydrogen per anode. For hydrides other than group 1 and 2 metals, the term is misleading given the low electronegativity of hydrogen. An exception in group 2 hydrides is BeH2, which is polymeric. In lithium aluminum hydride, the AlH-4 anion carries hydride centers firmly attached to Al(III). Although hydrides can form in almost all main group elements, the number and combination of possible compounds vary greatly; for example, over 100 binary borane hydrides and only one binary aluminum hydride are known. Binary indium hydride has not yet been identified, although large complexes exist. In inorganic chemistry, hydrides can also serve as bridging ligands that link two metal centers in a coordination complex. This function is especially 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 gives H+, which contains no electrons and no nucleus, which usually consists of a single proton. This is why H+ is often referred to as a proton. This view is central to the discussion of acids. According to the Bronsted-Lowry theory, acids are proton donors and bases are proton acceptors. The naked 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 plasmas, 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 designated "H+" without any meaning 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" (H 3 O+). However, even in this case, such solvated hydrogen cations are more realistically perceived as organized clusters that form species close to H 9O+4. Other oxonium ions are found when water is in an acidic solution with other solvents. Despite being exotic on Earth, one of the most common ions in the universe is H+3, known as protonated molecular hydrogen or the 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 common isotope of hydrogen, with an abundance of over 99.98%. Since the nucleus of this isotope consists of only one proton, it is given the descriptive but rarely used formal name protium. 2H, the other stable isotope of hydrogen, is known as deuterium and contains one proton and one neutron in the nucleus. It is believed that all the deuterium in the universe was produced during the Big Bang and has existed since that time until now. Deuterium is not a radioactive element and does not pose a significant toxicity hazard. Water enriched in molecules that include deuterium instead of normal hydrogen is called heavy water. Deuterium and its compounds are used as a non-radioactive label 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 into 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 a small amount of radiation from escaping. A small amount of tritium is produced naturally by the interaction of cosmic rays with atmospheric gases; tritium was also released during testing nuclear weapons. 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 labeling experiments as a radioactive label. Hydrogen is the only element that has different names for its isotopes that are in common use today. During the early study of radioactivity, various heavy radioactive isotopes were given 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 thus not available for protium. In its nomenclature guidelines, the International Union of Pure and Applied Chemistry allows any of the symbols from D, T, 2H, and 3H to be used, although 2H and 3H are preferred. The exotic atom muonium (symbol Mu), consisting of an antimuon and an electron, is also sometimes considered a light radioisotope of hydrogen due to the mass difference between the antimuon and the electron, which was discovered in 1960. During the lifetime of the muon, 2.2 μs, muonium can enter compounds such as muonium chloride (MuCl) or sodium muonide (NaMu), similarly to hydrogen chloride and sodium hydride, respectively.

Story

Discovery and use

In 1671, Robert Boyle discovered and described the reaction between iron filings and dilute acids that results in hydrogen gas. In 1766, Henry Cavendish was the first to recognize hydrogen gas as a discrete substance, naming the gas "flammable air" because of the metal-acid reaction. He suggested that "flammable air" was in fact identical to a hypothetical substance called "phlogiston" and found again in 1781 that the gas produced water when burned. It is believed that it was he 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 water was formed when hydrogen was burned. Lavoisier produced hydrogen for his conservation of mass experiments by reacting a stream of steam with metallic iron through an incandescent lamp heated in a fire. The anaerobic oxidation of iron by water protons at high temperature 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 first liquefied by James Dewar in 1898 using regenerative refrigeration and his invention, the vacuum flask. The following year, he produced solid hydrogen. Deuterium was discovered in December 1931 by Harold Uray and tritium was prepared in 1934 by Ernest Rutherford, Mark Oliphant and Paul Harteck. Heavy water, which is made up of deuterium instead of ordinary hydrogen, was discovered by Yurey'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. Döbereiner's steel (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 of air traffic after Henri Giffard's invention of the first hydrogen-lifted airship in 1852. The German Count Ferdinand von Zeppelin promoted the idea of ​​rigid airships lifted into the air by hydrogen, which were later called Zeppelins; the first of these flew for the first time in 1900. Regularly scheduled flights began in 1910 and by the outbreak of World War I in August 1914 they had 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 supposed to improve aviation safety, but the US government refused to sell gas for this purpose, so H2 was used in the Hindenburg airship, which was destroyed in the Milan fire in New Jersey May 6, 1937. The incident was broadcast live on the radio and videotaped. It was widely assumed that the cause of the ignition was a hydrogen leak, however subsequent studies indicate that the aluminized fabric coating was ignited by static electricity. But by this time, hydrogen's reputation as a lifting gas had already been damaged. That same year, the first hydrogen-cooled turbogenerator with hydrogen gas as the coolant in the rotor and stator went into operation in 1937 in Dayton, Ohio, by the 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 aboard 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 part 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

Because of its simple atomic structure of only a proton and an electron, the hydrogen atom, along with the spectrum of light created from or absorbed by it, has been central to the development of atomic structure theory. 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 soon followed the physical treatment of the hydrogen atom in quantum mechanics in mid-2020. One of the first quantum effects that was clearly observed (but not understood at that time) was Maxwell's observation involving hydrogen half a century before there was a full quantum mechanical theory. Maxwell noted that specific heat H2 irreversibly departs from the diatomic gas below room temperature and begins to more and more resemble the specific heat capacity of the monatomic gas at cryogenic temperatures. According to quantum theory, this behavior arises from the spacing of (quantized) rotational energy levels, which are especially widely spaced in H2 due to its low mass. These widely spaced levels prevent an equal division of thermal energy into rotational motion in hydrogen at low temperatures. Diatom gases, which are composed 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 obtained 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 over 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 undiscovered 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 turning stars on through the proton-proton reaction and nuclear fusion of the CNO cycle. Throughout the world, hydrogen occurs mainly in atomic and plasma states with properties quite 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 (generating light from the Sun and other stars). Charged particles are strongly affected by magnetic and electric fields. For example, in the solar wind, they interact with the Earth's magnetosphere, creating Birkeland currents and the aurora. Hydrogen is in a neutral atomic state in the interstellar medium. The large amount of neutral hydrogen found in evanescent Liman-alpha systems is believed 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 the Earth's gravity more easily than heavier gases. However, hydrogen is the third most abundant element on the Earth's surface, existing primarily in the form of chemical compounds such as hydrocarbons and water. Hydrogen gas is produced by some bacteria and algae and is a natural component of the 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 environment due to low temperature and density. H+3 is one of the most abundant ions in the universe and plays a prominent role in the chemistry of the interstellar medium. Neutral triatomic hydrogen H3 can exist only in an excited form and is unstable. In contrast, the positive molecular hydrogen ion (H+2) is a rare molecule in the universe.

Hydrogen production

H2 is produced in chemical and biological laboratories, often as a by-product 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 the removal of 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 (steam) reacts with methane to produce carbon monoxide and H2.

CH4 + H2O → CO + 3 H2

This reaction works best at low pressures, but can still 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 superheat cleaning systems perform better at higher pressures. The product mixture is known as "synthesis gas" 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 usually uses an excess of H2O. Additional hydrogen can be recovered from the steam using carbon monoxide through a water gas shift 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 the partial oxidation of hydrocarbons:

2 CH4 + O2 → 2 CO + 4 H2

And the coal reaction, which can serve as a prelude to the shift 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 the production of ammonia, hydrogen is generated from natural gas. Salt solution electrolysis to produce chlorine also produces hydrogen as a by-product.

metallic acid

In the laboratory, H2 is usually made 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

Water electrolysis is a simple way to produce hydrogen. A low voltage current flows through the water and oxygen gas is generated at the anode while hydrogen gas is generated at the cathode. Typically, the cathode is made from platinum or another inert metal in the production of hydrogen for storage. If, however, the gas is to be burned in situ, the presence of oxygen is desirable to promote combustion, and therefore both electrodes will be made of inert metals. (For example, iron oxidizes and therefore reduces the amount of oxygen released). The theoretical maximum efficiency (electricity used in relation to the energy value of 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 alumina, but the expensive gallium, which prevents oxide skin from forming on the pellets, can be reused. This has important potential implications for the economics of hydrogen, since hydrogen can be produced locally and does not need to be transported.

Thermochemical properties

There are more than 200 thermochemical cycles that can be used to separate water, about a dozen of these cycles, such as the iron oxide cycle, the cerium (IV) oxide cycle, the cerium (III) oxide cycle, the zinc-zinc oxide cycle, the sulfur iodine cycle, the copper cycle, and chlorine and sulfur hybrid 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 those in France, Germany, Greece, Japan and the USA) are developing thermochemical methods for producing hydrogen from solar energy and water.

Anaerobic corrosion

Under anaerobic conditions, iron and steel alloys are slowly oxidized by water protons while being reduced in 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 the anaerobic corrosion of iron and steel in anoxic conditions. groundwater and when restoring soils below the groundwater level.

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 in the process of serpentinization by anaerobic oxidation by water protons (H+) of iron silicate (Fe2 +) present in the crystal lattice of fayalite (Fe2SiO4, olivine-iron minal). 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 closely resembles the Shikorra reaction observed in the anaerobic oxidation of iron hydroxide in contact with water.

Formation in transformers

Of all the hazardous gases produced in power transformers, hydrogen is the most common and is generated in the majority of faults; thus, the formation of hydrogen is an early sign of 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 greatest use of H2 is 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 other important uses. H2 is used as a hydrogenating agent, in particular to increase the saturation level of unsaturated fats and oils (found in items such as margarine), and in methanol production. 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 embrittles many metals, complicating the design of pipelines and storage tanks. In addition to being used as a reagent, H2 has a wide range of applications in physics and engineering. It is used as a shielding gas in welding methods such as atomic hydrogen welding. H2 is used as a 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 research into superconductivity. Because H2 is lighter than air, at just over 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 neat 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 a permitted food additive (E 949) that allows food leak testing, 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 field of chemistry and biology in the study of the isotope effects of the reaction. Tritium (hydrogen-3), produced in nuclear reactors, is used in the manufacture of hydrogen bombs, as an isotope marker 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 refrigerant 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 currently far from mature. The energy of the Sun comes from the 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 it takes to burn it, so in these cases the hydrogen functions as an energy carrier, similar to a battery. Hydrogen can be obtained 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 conventional energy sources, 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 could be done at the point of production of H2 from fossil fuels. Hydrogen used in transport will burn relatively cleanly, with some NOx emissions but no carbon emissions. However, the infrastructure cost associated with a full conversion to a hydrogen economy will be substantial. Fuel cells can turn 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 to 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 types of 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 two protons and two electrons components. The creation of hydrogen gas occurs by transferring reducing equivalents produced by the fermentation of pyruvate to 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.