What is hydrogen? Boiling of hydrogen.

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 an integral part of many complex compounds, a 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 oxidizing and reducing properties. In addition, after donating an electron, it remains with 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, 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 of alkali 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 in large quantities it 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 volumes 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. The general formula is 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 its high importance for nature and humans, as well as for all living beings.

- this is the best solvent

As mentioned above, the common name for this substance is 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.

It is in the aquatic environment that 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.

Prevalence in nature. V. is widespread in nature; its content in the earth's crust (lithosphere and hydrosphere) is 1% by mass and 16% by number of atoms. V. is part of the most common substance on Earth - water (11.19% of V. by weight), in the composition of compounds that make up coal, oil, natural gases, clays, as well as animal and plant organisms (i.e., in the composition proteins, nucleic acids, fats, carbohydrates, etc.). In the free state, V. is extremely rare; it is found in small quantities in volcanic and other natural gases. Minor amounts of free hydrogen (0.0001% by number of atoms) are present in the atmosphere. In the near-Earth space, radiation forms the Earth's internal (“proton”) radiation belt in the form of a flow of protons. In space, V. is the most common element. In the form of plasma, it makes up about half the mass of the Sun and most stars, the bulk of the gases of the interstellar medium and gaseous nebulae. V. is present in the atmosphere of a number of planets and in comets in the form of free H2, methane CH4, ammonia NH3, water H2O, radicals such as CH, NH, OH, SiH, PH, etc. In the form of a flow of protons, energy is part of the corpuscular radiation of the Sun and cosmic rays.

Isotopes, atom and molecule. Ordinary vitriol consists of a mixture of two stable isotopes: light vitriol, or protium (1H), and heavy vitriol, or deuterium (2H, or D). In natural compounds, there are on average 6800 1H atoms per 1 2H atom. A radioactive isotope has been artificially produced - superheavy V., or tritium (3H, or T), with soft β-radiation and a half-life T1/2 = 12.262 years. In nature, tritium is formed, for example, from atmospheric nitrogen under the influence of cosmic ray neutrons; in the atmosphere it is negligibly small (4-10-15% of the total number of V atoms). An extremely unstable isotope 4H was obtained. The mass numbers of the isotopes 1H, 2H, 3H and 4H, respectively 1,2, 3 and 4, indicate that the nucleus of a protium atom contains only 1 proton, deuterium - 1 proton and 1 neutron, tritium - 1 proton and 2 neutrons, 4H - 1 proton and 3 neutrons. The large difference in the masses of the isotopes of V. determines a more noticeable difference in their physical and chemical properties than in the case of isotopes of other elements.

The V. atom has the simplest structure among the atoms of all other elements: it consists of a nucleus and one electron. The binding energy of an electron with a nucleus (ionization potential) is 13.595 eV. A neutral atom can also add a second electron, forming a negative ion H-; in this case, the binding energy of the second electron with a neutral atom (electron affinity) is 0.78 eV. Quantum mechanics makes it possible to calculate all possible energy levels of an atom and, therefore, give a complete interpretation of its atomic spectrum. The V atom is used as a model atom in quantum mechanical calculations of the energy levels of other, more complex atoms. Molecule B. H2 consists of two atoms connected by a covalent chemical bond. The energy of dissociation (i.e., decay into atoms) is 4.776 eV (1 eV = 1.60210-10-19 J). The interatomic distance at the equilibrium position of the nuclei is 0.7414-Å. At high temperatures, molecular hydrogen dissociates into atoms (the degree of dissociation at 2000°C is 0.0013, at 5000°C 0.95). Atomic V. is also formed in various chemical reactions (for example, by the action of Zn on hydrochloric acid). However, the existence of hydrogen in the atomic state lasts only a short time; the atoms recombine into H2 molecules.

Physical and chemical properties. V. is the lightest of all known substances (14.4 times lighter than air), density 0.0899 g/l at 0°C and 1 atm. Helium boils (liquefies) and melts (solidifies), respectively, at -252.6°C and -259.1°C (only helium has lower melting and boiling points). The critical temperature of water is very low (-240°C), so its liquefaction is fraught with great difficulties; critical pressure 12.8 kgf/cm2 (12.8 atm), critical density 0.0312 g/cm3. Of all gases, V. has the greatest thermal conductivity, equal to 0.174 W/(m-K) at 0°C and 1 atm, i.e. 4.16-0-4 cal/(s-cm-°C). The specific heat capacity of V. at 0°C and 1 atm Ср 14.208-103 J/(kg-K), i.e. 3.394 cal/(g-°C). V. is slightly soluble in water (0.0182 ml/g at 20°C and 1 atm), but well soluble in many metals (Ni, Pt, Pd, etc.), especially in palladium (850 volumes per 1 volume of Pd) . V.'s solubility 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 carbon with carbon (so-called decarbonization). Liquid V. is very light (density at -253°C 0.0708 g/cm3) and fluid (viscosity at -253°C 13.8 spuaz).

In most compounds, V. exhibits a valence (more precisely, oxidation state) +1, like sodium and other alkali metals; usually it is considered as an analogue of these metals, leading 1 gram. Mendeleev's system. However, in metal hydrides, the B ion is negatively charged (oxidation state -1), i.e., the Na+H- hydride is structured similarly to the Na+Cl- chloride. This and some other facts (the similarity of the physical properties of V. and halogens, the ability of halogens to replace V. in organic compounds) give grounds to classify V. also in the VII group of the periodic table (for more details, see the Periodic Table of Elements). Under normal conditions, molecular V. is relatively little active, directly combining only with the most active of nonmetals (with fluorine, and in the light with chlorine). However, when heated, it reacts with many elements. Atomic V. has increased chemical activity compared to molecular. With oxygen, V. forms water: H2 + 1/2O2 = H2O with the release of 285.937-103 J/mol, i.e. 68.3174 kcal/mol of heat (at 25°C and 1 atm). At normal temperatures the reaction proceeds extremely slowly, above 550°C it explodes. The explosive limits of a hydrogen-oxygen mixture are (by volume) from 4 to 94% H2, and of a hydrogen-air mixture - from 4 to 74% H2 (a mixture of 2 volumes of H2 and 1 volume of O2 is called detonating gas). V. is used to reduce many metals, as it removes oxygen from their oxides:

CuO + H2 = Cu + H2O,
Fe3O4 + 4H2 = 3Fe + 4H2O, etc.
With halogens, V. forms hydrogen halides, for example:
H2 + Cl2 = 2HCl.

At the same time, V. explodes with fluorine (even in the dark and at -252°C), reacts with chlorine and bromine only when illuminated or heated, and with iodine only when heated. V. reacts with nitrogen to form ammonia: 3H2 + N2 = 2NH3 only on a catalyst and at elevated temperatures and pressures. When heated, V. reacts vigorously with sulfur: H2 + S = H2S (hydrogen sulfide), much more difficult with selenium and tellurium. V. can react with pure carbon without a catalyst only at high temperatures: 2H2 + C (amorphous) = CH4 (methane). V. reacts directly with certain metals (alkali, alkaline earth, etc.), forming hydrides: H2 + 2Li = 2LiH. Of great practical importance are the reactions of hydrogen with carbon monoxide, in which various organic compounds are formed, depending on temperature, pressure, and catalyst, for example HCHO, CH3OH, etc. (see Carbon monoxide). Unsaturated hydrocarbons react with hydrogen, becoming saturated, for example: CnH2n + H2 = CnH2n+2 (see Hydrogenation).

Hydrogen storage.

Gladysheva Marina Alekseevna, 10A, school No. 75, Chernogolovka. Report at the conference "Start in Science", MIPT, 2004.

The attractiveness of hydrogen as a universal energy carrier is determined by its environmental friendliness, flexibility and efficiency of energy conversion processes involving its participation. Technologies for multi-scale hydrogen production are quite well developed and have an almost unlimited raw material base. However, the low density of hydrogen gas, the low temperature of its liquefaction, as well as the high explosion hazard, combined with a negative impact on the properties of structural materials, bring to the fore the problems of developing effective and safe hydrogen storage systems - these are the problems that are currently hindering the development of hydrogen energy and technology .

In accordance with the classification of the US Department of Energy, hydrogen fuel storage methods can be divided into 2 groups:

The first group includes physical methods that use physical processes (mainly compression or liquefaction) to convert hydrogen gas into a compact state. Hydrogen stored using physical methods consists of H 2 molecules , weakly interacting with the storage environment. The following physical methods for storing hydrogen have been implemented today:

Compressed hydrogen gas:

gas cylinders;

stationary massive storage systems, including underground tanks;

storage in pipelines;

glass microspheres.

Liquid hydrogen: stationary and transport cryogenic containers.

IN chemical methods, hydrogen storage is ensured by physical or chemical processes of its interaction with certain materials. These methods are characterized by the strong interaction of molecular or atomic hydrogen with the material of the storage medium. This group of methods mainly includes the following:

Adsorption:

zeolites and related compounds;

Activated carbon;

hydrocarbon nanomaterials.

Absorption per volume of material(metal hydrides)

Chemical interaction:

alonates;

fullerenes and organic hydrides;

ammonia;

sponge iron;

water-reactive alloys based on aluminum and silicon.

Hydrogen gas storage is no more complex problem than natural gas storage. In practice, gas tanks, natural underground reservoirs (aquifers, depleted oil and gas fields), and storage facilities created by underground atomic explosions are used for this purpose. The fundamental possibility of storing hydrogen gas in salt caverns created by dissolving salt with water through boreholes has been proven.

To store hydrogen gas at pressures up to 100 MPa, welded vessels with two- or multi-layer walls are used. The inner wall of such a vessel is made of austenitic stainless steel or other material compatible with hydrogen under high pressure conditions, the outer layers are made of high-strength steels. For these purposes, seamless thick-walled vessels made of low-carbon steels designed for pressures of up to 40 - 70 MPa are also used.

The storage of hydrogen gas in gas holders with a water pool (wet gas holders), constant pressure piston gas holders (dry gas holders), and constant volume gas holders (high pressure tanks) has become widespread. Cylinders are used to store small quantities of hydrogen.

It should be borne in mind that wet as well as dry (piston) gas tanks of welded construction do not have sufficient tightness. According to the technical conditions, hydrogen leakage is allowed during normal operation of wet gas tanks with a capacity of up to 3000 m3 3 – about 1.65%, and with a capacity from 3000 m 3 and more - about 1.1% per day (based on the nominal volume of the gas tank).

One of the most promising ways to store large quantities of hydrogen is to store it in aquifers. Annual losses with this storage method range from 1 to 3%. This amount of losses is confirmed by the experience of natural gas storage.

Hydrogen gas can be stored and transported in steel vessels under pressure up to 20 MPa. Such containers can be transported to the point of consumption on automobile or railway platforms, both in standard containers and in specially designed containers.

For storage and transportation of small quantities of compressed hydrogen at temperatures from –50 to +60 0 C use steel seamless cylinders of small capacity up to 12 dm 3 and average capacity 20 – 50 dm 3 with working pressure up to 20 MPa. The valve body is made of brass. The cylinders are painted dark green and have the inscription “Hydrogen” in red.

Hydrogen storage cylinders are quite simple and compact. However, to store 2 kg N 2 bolts weighing 33 kg are required. Progress in materials science makes it possible to reduce the mass of the cylinder material to 20 kg per 1 kg of hydrogen, and in the future it is possible to reduce it to 8–10 kg. So far, the mass of hydrogen when stored in cylinders is approximately 2–3% of the mass of the cylinder itself.

Large quantities of hydrogen can be stored in large pressurized gas tanks. Gas tanks are usually made of carbon steel. The working pressure in them usually does not exceed 10 MPa. Due to the low density of hydrogen gas, storing it in such containers is beneficial only in relatively small quantities. Increasing the pressure above the specified value, for example, to hundreds of mega Pascals, firstly, causes difficulties associated with hydrogen corrosion of carbon steels, and, secondly, leads to a significant increase in the cost of such containers.

For storing very large quantities of hydrogen, a cost-effective method is to store depleted gas and aquifers. There are more than 300 underground gas storage facilities in the United States.

Hydrogen gas in very large quantities is stored in salt caverns 365 m deep at a hydrogen pressure of 5 MPa, in porous water-filled structures containing up to 20 10 6 m 3 hydrogen.

Experience of long-term storage (more than 10 years) in underground gas storage facilities of gas containing 50% hydrogen has shown the full possibility of its storage without noticeable leaks. Layers of clay soaked in water can provide hermetically sealed storage due to the weak dissolution of hydrogen in water.

Liquid hydrogen storage

Among the many unique properties of hydrogen that are important to consider when storing it in liquid form, one is especially important. Hydrogen in the liquid state is found in a narrow temperature range: from the boiling point of 20K to the freezing point of 17K, when it turns into a solid state. If the temperature rises above its boiling point, hydrogen instantly changes from liquid to gas.

To prevent local overheating, vessels that are filled with liquid hydrogen should be pre-cooled to a temperature close to the boiling point of hydrogen, only then can they be filled with liquid hydrogen. To do this, cooling gas is passed through the system, which is associated with high consumption of hydrogen to cool the container.

The transition of hydrogen from liquid to gaseous state is associated with inevitable losses from evaporation. The cost and energy content of the evaporated gas is significant. Therefore, organizing the use of this gas from an economic and safety point of view is necessary. According to the conditions for safe operation of a cryogenic vessel, it is necessary that after reaching the maximum operating pressure in the container, the gas space is at least 5%.

There are a number of requirements for liquid hydrogen storage tanks:

the design of the tank must ensure strength and reliability, long-term safe operation;

the consumption of liquid hydrogen for pre-cooling the storage facility before filling it with liquid hydrogen should be minimal;

The storage tank must be equipped with a means for rapid filling with liquid hydrogen and rapid dispensing of the stored product.

The main part of the cryogenic hydrogen storage system is thermally insulated vessels, the mass of which is approximately 4 - 5 times less per 1 kg of stored hydrogen than with cylinder storage under high pressure. In cryogenic storage systems for liquid hydrogen, 1 kg of hydrogen accounts for 6–8 kg of the mass of a cryogenic vessel, and in terms of volumetric characteristics, cryogenic vessels correspond to the storage of gaseous hydrogen under a pressure of 40 MPa.

Liquid hydrogen is stored in large quantities in special storage facilities with a volume of up to 5 thousand m 3 . Large spherical storage facility for liquid hydrogen with a volume of 2850 m 3 has an internal diameter of the aluminum sphere of 17.4 m 3 .

Storage and transportation of hydrogen in a chemically bound state

The advantages of storing and transporting hydrogen in the form of ammonia, methanol, ethanol over long distances are the high density of the volumetric hydrogen content. However, in these forms of hydrogen storage, the storage medium is used once. The liquefaction temperature of ammonia is 239.76 K, the critical temperature is 405 K, so at normal temperature, ammonia liquefies at a pressure of 1.0 MPa and can be transported through pipes and stored in liquid form. Basic The ratios are given below:

1 m 3 N 2 (g) » 0.66 m 3 NH 3 » 0?75 dm 3 H 2 (l);

1 t NH 3 » 1975 m 3 N 2 + 658 m 3 N 2 – 3263 MJ;

2NH 3 ?N 2 + 3H 2 – 92 kJ.

Dissociators for the decomposition of ammonia (crackers), which occurs at temperatures of approximately 1173 - 1073 K and atmospheric pressure, use a spent iron catalyst to synthesize ammonia. To produce one kg of hydrogen, 5.65 kg of ammonia is consumed. As for the heat consumption for the dissociation of ammonia when using this heat from the outside, the heat of combustion of the resulting hydrogen can be up to 20% higher than the heat of combustion of the ammonia used in the decomposition process. If hydrogen obtained in the process is used for the dissociation process, then the efficiency of such a process (the ratio of the heat of the resulting gas to the heat of combustion of the consumed ammonia) does not exceed 60 - 70%.

Hydrogen from methanol can be obtained according to two schemes: either by catalytic decomposition:

CH 3 OH? CO+2H 2 – 90 kJ

followed by catalytic conversion of CO or catalytic steam conversion in one stage:

H 2 O + CH 3 OH? CO 2 + 3H 2 – 49 kJ.

Typically, the process uses a zinc-chromium catalyst for methanol synthesis. The process occurs at 573 – 673 K. Methanol can be used as fuel for conversion processes. In this case, the efficiency of the hydrogen production process is 65–70% (the ratio of the heat of the produced hydrogen to the heat of combustion of the consumed methanol); if heat for the process of producing hydrogen is supplied from the outside, the heat of combustion of hydrogen obtained by catalytic decomposition is 22%, and that of hydrogen obtained by steam reforming is 15% higher than the heat of combustion of consumed methanol.

It should be added to the above that when creating an energy-technological scheme using waste heat and the use of hydrogen obtained from methanol, ammonia or ethanol, it is possible to obtain a process efficiency higher than when using these products as synthetic liquid fuels. Thus, with direct combustion of methanol and a gas turbine unit, the efficiency is 35%, when, due to the heat of exhaust gases, evaporation and catalytic conversion of methanol and combustion of the CO + H mixture are carried out 2 The efficiency increases to 41.30%, and when carrying out steam reforming and combustion of the resulting hydrogen - up to 41.9%.

Hydride hydrogen storage system

By storing hydrogen in hydride form, there is no need for bulky and heavy cylinders required when storing compressed hydrogen gas, or difficult to manufacture and expensive vessels for storing liquid hydrogen. When storing hydrogen in the form of hydrides, the volume of the system is reduced by approximately 3 times compared to the volume of storage in cylinders. Hydrogen transportation is simplified. There are no costs for conversion and liquefaction of hydrogen.

Hydrogen can be obtained from metal hydrides by two reactions: hydrolysis and dissociation.

By hydrolysis it is possible to obtain twice as much hydrogen as is present in the hydride. However, this process is practically irreversible. The method of producing hydrogen by thermal dissociation of a hydride makes it possible to create hydrogen batteries, for which a slight change in temperature and pressure in the system causes a significant change in the equilibrium of the hydride formation reaction.

Stationary devices for storing hydrogen in the form of hydrides do not have strict restrictions on mass and volume, so the limiting factor in the choice of a particular hydride will, in all likelihood, be its cost. For some applications, vanadium hydride may be useful, since it dissociates well at a temperature close to 270 K. Magnesium hydride is relatively inexpensive, but has a relatively high dissociation temperature of 560 - 570 K and a high heat of formation. The iron-titanium alloy is relatively inexpensive, and its hydride dissociates at temperatures of 320 - 370 K with a low heat of formation. The use of hydrides has significant safety advantages. A damaged hydrogen hydride vessel poses significantly less danger than a damaged liquid hydrogen tank or pressure vessel filled with hydrogen.

Currently, at the Institute of Chemical Physics of the Russian Academy of Sciences in Chernogolovka, work is underway to create hydrogen batteries based on metal hydrides.

Bibliography :

1. Directory. "Hydrogen. Properties, receipt, storage, transportation, application.” Moscow “Chemistry” - 1989

2. “Review of hydrogen storage methods.” Institute of Materials Science Problems of the National Academy of Sciences of Ukraine. http://shp.by.ru/sci/fullerene/rorums/ichms/2003/

• Designation - H (Hydrogen);
• Latin name - Hydrogenium;
• Period - I;
• Group - 1 (Ia);
• Atomic mass - 1.00794;
• Atomic number - 1;
• Atomic radius = 53 pm;
• Covalent radius = 32 pm;
• Electron distribution - 1s 1;
• melting temperature = -259.14°C;
• boiling point = -252.87°C;
• Electronegativity (according to Pauling/according to Alpred and Rochow) = 2.02/-;
• Oxidation state: +1; 0; -1;
• Density (no.) = 0.0000899 g/cm 3 ;
• Molar volume = 14.1 cm 3 /mol.

Binary compounds of hydrogen with oxygen:

Hydrogen (“giving birth to water”) was discovered by the English scientist G. Cavendish in 1766. It is the simplest element in nature - a hydrogen atom has a nucleus and one electron, which is probably why hydrogen is the most abundant element in the Universe (accounting for more than half the mass of most stars).

About hydrogen we can say that “the spool is small, but expensive.” Despite its “simplicity,” hydrogen provides energy to all living beings on Earth - a continuous thermonuclear reaction takes place on the Sun during which one helium atom is formed from four hydrogen atoms, this process is accompanied by the release of a colossal amount of energy (for more details, see Nuclear fusion).

In the earth's crust, the mass fraction of hydrogen is only 0.15%. Meanwhile, the overwhelming majority (95%) of all chemical substances known on Earth contain one or more hydrogen atoms.

In compounds with non-metals (HCl, H 2 O, CH 4 ...), hydrogen gives up its only electron to more electronegative elements, exhibiting an oxidation state of +1 (more often), forming only covalent bonds (see Covalent bond).

In compounds with metals (NaH, CaH 2 ...), hydrogen, on the contrary, accepts another electron into its only s-orbital, thus trying to complete its electronic layer, exhibiting an oxidation state of -1 (less often), often forming an ionic bond (see Ionic bond), because the difference in electronegativity of the hydrogen atom and the metal atom can be quite large.

H 2

In the gaseous state, hydrogen exists in the form of diatomic molecules, forming a nonpolar covalent bond.

Hydrogen molecules have:

• great mobility;
• great strength;
• low polarizability;
• small size and weight.

Properties of hydrogen gas:

• the lightest gas in nature, colorless and odorless;
• poorly soluble in water and organic solvents;
• dissolves in small amounts in liquid and solid metals (especially platinum and palladium);
• difficult to liquefy (due to its low polarizability);
• has the highest thermal conductivity of all known gases;
• when heated, it reacts with many non-metals, exhibiting the properties of a reducing agent;
• at room temperature it reacts with fluorine (an explosion occurs): H 2 + F 2 = 2HF;
• reacts with metals to form hydrides, exhibiting oxidizing properties: H 2 + Ca = CaH 2 ;

In compounds, hydrogen exhibits its reducing properties much more strongly than its oxidizing properties. Hydrogen is the most powerful reducing agent after coal, aluminum and calcium. The reducing properties of hydrogen are widely used in industry to obtain metals and nonmetals (simple substances) from oxides and gallides.

Fe 2 O 3 + 3H 2 = 2Fe + 3H 2 O

Reactions of hydrogen with simple substances

Hydrogen accepts an electron, playing a role reducing agent, in reactions:

• With oxygen(when ignited or in the presence of a catalyst), in a ratio of 2:1 (hydrogen:oxygen) an explosive detonating gas is formed: 2H 2 0 +O 2 = 2H 2 +1 O+572 kJ
• With gray(when heated to 150°C-300°C): H 2 0 +S ↔ H 2 +1 S
• With chlorine(when ignited or irradiated with UV rays): H 2 0 +Cl 2 = 2H +1 Cl
• With fluorine: H 2 0 +F 2 = 2H +1 F
• With nitrogen(when heated in the presence of catalysts or at high pressure): 3H 2 0 +N 2 ↔ 2NH 3 +1

Hydrogen donates an electron, playing a role oxidizing agent, in reactions with alkaline And alkaline earth metals with the formation of metal hydrides - salt-like ionic compounds containing hydride ions H - these are unstable white crystalline substances.

Ca+H 2 = CaH 2 -1 2Na+H 2 0 = 2NaH -1

It is not typical for hydrogen to exhibit an oxidation state of -1. When reacting with water, the hydrides decompose, reducing water to hydrogen. The reaction of calcium hydride with water is as follows:

CaH 2 -1 +2H 2 +1 0 = 2H 2 0 +Ca(OH) 2

Reactions of hydrogen with complex substances

• at high temperatures, hydrogen reduces many metal oxides: ZnO+H 2 = Zn+H 2 O
• methyl alcohol is obtained by the reaction of hydrogen with carbon monoxide (II): 2H 2 +CO → CH 3 OH
• In hydrogenation reactions, hydrogen reacts with many organic substances.

The equations of chemical reactions of hydrogen and its compounds are discussed in more detail on the page “Hydrogen and its compounds - equations of chemical reactions involving hydrogen.”

Applications of hydrogen

• in nuclear energy, hydrogen isotopes are used - deuterium and tritium;
• in the chemical industry, hydrogen is used for the synthesis of many organic substances, ammonia, hydrogen chloride;
• in the food industry, hydrogen is used in the production of solid fats through the hydrogenation of vegetable oils;
• for welding and cutting metals, the high combustion temperature of hydrogen in oxygen (2600°C) is used;
• in the production of some metals, hydrogen is used as a reducing agent (see above);
• since hydrogen is a light gas, it is used in aeronautics as a filler for balloons, aerostats, and airships;
• Hydrogen is used as a fuel mixed with CO.

Recently, scientists have been paying a lot of attention to the search for alternative sources of renewable energy. One of the promising areas is “hydrogen” energy, in which hydrogen is used as fuel, the combustion product of which is ordinary water.

Methods for producing hydrogen

Industrial methods for producing hydrogen:

• methane conversion (catalytic reduction of water vapor) with water vapor at high temperature (800°C) on a nickel catalyst: CH 4 + 2H 2 O = 4H 2 + CO 2 ;
• conversion of carbon monoxide with water vapor (t=500°C) on a Fe 2 O 3 catalyst: CO + H 2 O = CO 2 + H 2 ;
• thermal decomposition of methane: CH 4 = C + 2H 2;
• gasification of solid fuels (t=1000°C): C + H 2 O = CO + H 2 ;
• electrolysis of water (a very expensive method that produces very pure hydrogen): 2H 2 O → 2H 2 + O 2.

Laboratory methods for producing hydrogen:

• action on metals (usually zinc) with hydrochloric or dilute sulfuric acid: Zn + 2HCl = ZCl 2 + H 2 ; Zn + H 2 SO 4 = ZnSO 4 + H 2;
• interaction of water vapor with hot iron filings: 4H 2 O + 3Fe = Fe 3 O 4 + 4H 2.

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 17th 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 importance of hydrogen in chemical processes occurring on Earth is almost as great as that of 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, which is available in a free state, is obtained physically - by separation from liquid air. Almost all hydrogen is 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 (under conditions of the interstellar medium - with characteristic times up to cosmological ones), 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 the 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 the isotopes of chemical elements, the physical and chemical properties of hydrogen isotopes differ from each other the most. 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, such as 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 by 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 the volume ratio of hydrogen and oxygen is 2:1, or hydrogen and air is 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(packing gas)

Food industry

Aviation industry

Hydrogen is very light and always rises in the air. Once upon a time, airships and balloons were 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 volumetric energy density, combustion 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”.