Substances with which hydrogen reacts. Physical properties of hydrogen. Properties and applications of hydrogen. Characteristic by position in pshe

Hydrogen (H) is very light chemical element, with a content of 0.9% by mass in the Earth's crust, and 11.19% in water.

Characterization of hydrogen

In terms of ease, it is the first among gases. Under normal conditions it is tasteless, colorless, and absolutely odorless. When it enters the thermosphere, it flies into space due to its low weight.

In the entire universe, it is the most numerous chemical element (75% of the total mass of substances). So much so that many stars in outer space are composed entirely of it. For example, the sun. Its main component is hydrogen. And heat and light are the result of the release of energy when the nuclei of the material merge. Also in space there are whole clouds of its molecules of various sizes, densities and temperatures.

Physical properties

High temperature and pressure significantly change its qualities, but under normal conditions it:

Has a high thermal conductivity when compared with other gases,

Non-toxic and poorly soluble in water,

With a density of 0.0899 g / l at 0 ° C and 1 atm.,

It turns into a liquid at a temperature of -252.8 ° C

It becomes hard at -259.1 ° C.,

Specific heat of combustion 120.9.106 J / kg.

To turn into liquid or solid state high pressure and very low temperatures are required. In a liquefied state, it is fluid and light.

Chemical properties

Under pressure and when cooled (-252.87 g. C), hydrogen takes on a liquid state, which is lighter in weight than any analogue. It takes up less space in it than in gaseous form.

He is a typical non-metal. In laboratories, it is produced by reacting metals (such as zinc or iron) with dilute acids. Under normal conditions, it is inactive and reacts only with active non-metals. Hydrogen can separate oxygen from oxides, and reduce metals from compounds. He and his mixtures form a hydrogen bond with some elements.

The gas is readily soluble in ethanol and in many metals, especially palladium. Silver does not dissolve it. Hydrogen can be oxidized during combustion in oxygen or in air, and by interaction with halogens.

When combined with oxygen, water is formed. If the temperature is normal, then the reaction is slow, if above 550 ° C - with an explosion (turns into an explosive gas).

Finding hydrogen in nature

Although there is a lot of hydrogen on our planet, it is not easy to find it in its pure form. Few can be found during volcanic eruptions, during oil production and in the place of decomposition of organic matter.

More than half of the total amount is in the composition with water. It is also included in the structure of oil, various clays, combustible gases, animals and plants (the presence in each living cell is 50% by the number of atoms).

The hydrogen cycle in nature

Every year, a colossal amount (billions of tons) of plant residues is decomposed in water bodies and soil, and this decomposition splashes a huge mass of hydrogen into the atmosphere. It is also released during any fermentation caused by bacteria, combustion and, along with oxygen, participates in the water cycle.

Applications of hydrogen

The element is actively used by humanity in its activities, so we have learned how to obtain it on an industrial scale for:

Meteorology, chemical production;

Margarine production;

As rocket fuel (liquid hydrogen);

Electric power industry for cooling electric generators;

Welding and cutting of metals.

The mass of hydrogen is used in the production of synthetic gasoline (to improve the quality of low-quality fuel), ammonia, hydrogen chloride, alcohols, and other materials. Nuclear power actively uses its isotopes.

The drug "hydrogen peroxide" is widely used in metallurgy, electronics industry, pulp and paper production, in the bleaching of linen and cotton fabrics, for the manufacture of hair dyes and cosmetics, polymers and in medicine for treating wounds.

The "explosive" nature of this gas can be a deadly weapon - hydrogen bomb... Its explosion is accompanied by the release of a huge amount of radioactive substances and is destructive for all living things.

Contact between liquid hydrogen and skin threatens severe and painful frostbite.

Consider what hydrogen is. The chemical properties and production of this non-metal are studied in the course of inorganic chemistry at school. It is this element that heads the periodic system of Mendeleev, and therefore deserves a detailed description.

Opening an item at a glance

Before considering physical and Chemical properties hydrogen, let's find out how this important element was found.

Chemists who worked in the sixteenth and seventeenth centuries repeatedly mentioned in their writings the combustible gas that is released when acids are exposed to active metals. In the second half of the eighteenth century, G. Cavendish managed to collect and analyze this gas, giving it the name "combustible gas".

The physical and chemical properties of hydrogen at that time were not studied. Only at the end of the eighteenth century did A. Lavoisier succeed in analyzing to establish that this gas can be obtained by analyzing water. A little later, he began to call the new element hydrogene, which means "giving birth to water." Hydrogen owes its modern Russian name to M.F.Soloviev.

Being in nature

The chemical properties of hydrogen can only be analyzed on the basis of its abundance in nature. This element is present in the hydro- and lithosphere, and is also a part of minerals: natural and associated gas, peat, oil, coal, oil shale. It is difficult to imagine an adult who would not know that hydrogen is an integral part of water.

In addition, this non-metal is found in animal organisms in the form of nucleic acids, proteins, carbohydrates, and fats. On our planet, this element is found in free form quite rarely, perhaps only in natural and volcanic gas.

In the form of plasma, hydrogen makes up about half the mass of stars and the Sun, and is also part of the interstellar gas. For example, in free form, as well as in the form of methane, ammonia, this non-metal is present in comets and even some planets.

Physical properties

Before considering the chemical properties of hydrogen, we note that under normal conditions it is a gaseous substance lighter than air and has several isotopic forms. It is almost insoluble in water and has a high thermal conductivity. Protium, which has a mass number of 1, is considered its lightest form. Tritium, which has radioactive properties, is formed in nature from atmospheric nitrogen when it is exposed to UV rays by neurons.

Features of the structure of the molecule

To consider the chemical properties of hydrogen, the reactions characteristic of it, let us dwell on the features of its structure. This diatomic molecule has a covalent non-polar chemical bond. The formation of atomic hydrogen is possible through the interaction of active metals with acid solutions. But in this form, this non-metal is able to exist only for a small time period, almost immediately it recombines into a molecular form.

Chemical properties

Consider the chemical properties of hydrogen. In most of the compounds that this chemical element forms, it exhibits an oxidation state of +1, which makes it similar to active (alkali) metals. The main chemical properties of hydrogen, which characterize it as a metal:

• interaction with oxygen to form water;
• reaction with halogens, accompanied by the formation of hydrogen halide;
• obtaining hydrogen sulfide when combined with sulfur.

Below is the equation of reactions characterizing the chemical properties of hydrogen. We draw attention to the fact that as a non-metal (with an oxidation state of -1), it acts only in a reaction with active metals, forming the corresponding hydrides with them.

At ordinary temperatures, hydrogen inactively interacts with other substances, so most of the reactions are carried out only after preliminary heating.

Let us dwell in more detail on some of the chemical interactions of the element that heads the periodic table of chemical elements of Mendeleev.

The reaction of water formation is accompanied by the release of 285.937 kJ of energy. At elevated temperatures (more than 550 degrees Celsius) this process accompanied by a strong explosion.

Among those chemical properties of gaseous hydrogen that have found significant application in industry, its interaction with metal oxides is of interest. It is through catalytic hydrogenation in modern industry that metal oxides are processed, for example, pure metal is isolated from iron scale (mixed iron oxide). This method allows for efficient processing of scrap metal.

The synthesis of ammonia, which involves the interaction of hydrogen with nitrogen in the air, is also in demand in the modern chemical industry. Among the conditions for the occurrence of this chemical interaction, we note pressure and temperature.

Conclusion

It is hydrogen that is inactive chemical under normal conditions. As the temperature rises, its activity increases significantly. This substance is in demand in organic synthesis. For example, ketones can be reduced to secondary alcohols by hydrogenation and aldehydes can be converted to primary alcohols. In addition, by hydrogenation, it is possible to convert unsaturated hydrocarbons of the ethylene and acetylene class into saturated compounds of the methane series. Hydrogen is rightfully considered a simple substance in demand in modern chemical production.

Hydrogen H is a chemical element, one of the most abundant in our Universe. The mass of hydrogen as an element in the composition of substances is 75% of the total content of atoms of another type. He enters into the most important and vital connection on the planet - water. A distinctive feature of hydrogen is also the fact that it is the first element in the periodic system of chemical elements of D.I.Mendeleev.

Discovery and exploration

The first mention of hydrogen in the writings of Paracelsus dates back to the sixteenth century. But its separation from the gas mixture of air and the study of the combustible properties were carried out already in the seventeenth century by the scientist Lemery. Hydrogen was thoroughly studied by an English chemist, physicist and naturalist who empirically proved that the mass of hydrogen is the smallest in comparison with other gases. In the subsequent stages of the development of science, many scientists worked with him, in particular Lavoisier, who called him "giving birth to water."

Characteristic by position in PSCE

Element opening periodic table DI Mendeleev, is hydrogen. The physical and chemical properties of the atom exhibit a certain duality, since hydrogen is simultaneously attributed to the first group, the main subgroup, if it behaves like a metal and gives up a single electron in the process of a chemical reaction, and to the seventh - in the case of complete filling of the valence shell, that is, negative particle, which characterizes it as similar to halogens.

Features of the electronic structure of the element

Properties complex substances, of which it is included, and the simplest substance H 2 are primarily determined by the electronic configuration of the hydrogen. The particle has one electron with Z = (-1), which rotates in its orbit around the nucleus containing one proton with unit mass and positive charge (+1). Its electronic configuration is written as 1s 1, which means the presence of one negative particle on the very first and only s-orbital for the hydrogen.

When an electron is detached or given up, and the atom of this element has such a property that it makes it related to metals, a cation is obtained. Essentially, a hydrogen ion is a positive elementary particle. Therefore, the hydrogen deprived of an electron is simply called a proton.

Physical properties

In short, hydrogen is a colorless, slightly soluble gas with a relative atomic mass of 2, 14.5 times lighter than air, with a liquefaction temperature of -252.8 degrees Celsius.

It can be easily seen from experience that H 2 is the lightest. To do this, it is enough to fill three balls with various substances - hydrogen, carbon dioxide, ordinary air - and simultaneously release them from your hand. The one filled with CO 2 will reach the ground the fastest, after which the inflated air mixture will go down, and the one containing H 2 will rise to the ceiling.

The small mass and size of hydrogen particles justifies its ability to penetrate through various substances... On the example of the same ball, this is easy to be convinced of; in a couple of days it will deflate itself, since the gas will simply pass through the rubber. Also, hydrogen can accumulate in the structure of some metals (palladium or platinum), and evaporate from it when the temperature rises.

The property of low solubility of hydrogen is used in laboratory practice to isolate it by displacing hydrogen (the table below contains the main parameters) determine the scope of its application and methods of production.

Parameter of an atom or molecule of a simple substance	Meaning
Atomic mass (molar mass)	1.008 g / mol
Electronic configuration	1s 1
Crystal cell	Hexagonal
Thermal conductivity	(300 K) 0.1815 W / (m K)
Density at n. at.	0.08987 g / l
Boiling temperature	-252.76 ° C
Specific heat of combustion	120.9 10 6 J / kg
Melting temperature	-259.2 ° C
Water solubility	18.8 ml / l

Isotopic composition

Like many other representatives periodic system chemical elements, hydrogen has several natural isotopes, that is, atoms with the same number of protons in the nucleus, but a different number of neutrons - particles with zero charge and unit mass. Examples of atoms with a similar property are oxygen, carbon, chlorine, bromine, and others, including radioactive ones.

Physical properties hydrogen 1 H, the most common of the representatives of this group, differ significantly from the same characteristics of its counterparts. In particular, the characteristics of the substances in which they are included differ. So, there is ordinary and deuterated water, containing in its composition, instead of a hydrogen atom with a single proton, deuterium 2 H - its isotope with two elementary particles: positive and uncharged. This isotope is twice as heavy as conventional hydrogen, which explains the dramatic difference in the properties of the compounds they make up. In nature, deuterium is found 3200 times less frequently than hydrogen. The third representative is tritium 3 H, in the nucleus it has two neutrons and one proton.

Methods for obtaining and isolating

Laboratory and industrial methods are quite different. So, in small quantities, gas is obtained mainly through reactions in which mineral substances are involved, and large-scale production in to a greater extent use organic synthesis.

The following chemical interactions are used in the laboratory:

In industrial interests, gas is obtained by such methods as:

1. Thermal decomposition of methane in the presence of a catalyst to its constituents simple substances(350 degrees reaches the value of such an indicator as temperature) - hydrogen H 2 and carbon C.
2. Passing vaporous water through coke at 1000 degrees Celsius to form carbon dioxide CO 2 and H 2 (the most common method).
3. Conversion of gaseous methane on a nickel catalyst at temperatures reaching 800 degrees.
4. Hydrogen is a by-product of electrolysis aqueous solutions potassium or sodium chlorides.

Chemical interactions: general provisions

The physical properties of hydrogen largely explain its behavior in reaction processes with this or that compound. The valency of hydrogen is 1, since it is located in the first group in the periodic table, and the oxidation state is different. In all compounds, except for hydrides, hydrogen in s.r. = (1+), in molecules of the type XH, XH 2, XH 3 - (1-).

The hydrogen gas molecule, formed by creating a generalized electron pair, consists of two atoms and is quite stable energetically, which is why it is somewhat inert under normal conditions and enters into a reaction when normal conditions change. Depending on the oxidation state of hydrogen in the composition of other substances, it can act as both an oxidizing agent and a reducing agent.

Substances with which it reacts and which forms hydrogen

Elemental interactions with the formation of complex substances (often at elevated temperatures):

1. Alkaline and alkaline earth metal + hydrogen = hydride.
2. Halogen + H 2 = hydrogen halide.
3. Sulfur + hydrogen = hydrogen sulfide.
4. Oxygen + H 2 = water.
5. Carbon + hydrogen = methane.
6. Nitrogen + H 2 = ammonia.

Interaction with complex substances:

1. Production of synthesis gas from carbon monoxide and hydrogen.
2. Reduction of metals from their oxides using Н 2.
3. Hydrogen saturation of unsaturated aliphatic hydrocarbons.

Hydrogen bond

The physical properties of hydrogen are such that, being in conjunction with an electronegative element, it allows it to form a special type of bond with the same atom from neighboring molecules that have lone electron pairs (for example, oxygen, nitrogen and fluorine). The clearest example, on which it is better to consider a similar phenomenon, is water. It can be said to be stitched with hydrogen bonds, which are weaker than covalent or ionic ones, but due to the fact that there are many of them, they have a significant effect on the properties of a substance. Essentially, hydrogen bonding is an electrostatic interaction that binds water molecules into dimers and polymers, justifying its high boiling point.

Hydrogen in mineral compounds

All contain a proton - a cation of an atom such as hydrogen. A substance whose acidic residue has an oxidation state greater than (-1) is called a polybasic compound. It contains several hydrogen atoms, which makes the dissociation in aqueous solutions multistage. Each subsequent proton is detached from the remainder of the acid more and more difficult. Its acidity is determined by the quantitative content of hydrogen in the medium.

Application in human activities

Cylinders with a substance, as well as containers with other liquefied gases, for example oxygen, have a specific appearance... They are painted a dark green with a bright red inscription "Hydrogen". Gas is pumped into a cylinder at a pressure of about 150 atmospheres. The physical properties of hydrogen, in particular the lightness of the gaseous aggregate state, are used to fill balloons, balloons, etc., in a mixture with helium.

Hydrogen, the physical and chemical properties of which people learned to use many years ago, is currently used in many industries. Most of it goes to the production of ammonia. Hydrogen also participates in (hafnium, germanium, gallium, silicon, molybdenum, tungsten, zirconium and others) from oxides, acting in the reaction as a reducing agent, hydrocyanic and hydrochloric acids, as well as an artificial liquid fuel. The food industry uses it to convert vegetable oils into solid fats.

Determined the chemical properties and use of hydrogen in various processes of hydrogenation and hydrogenation of fats, coal, hydrocarbons, oils and fuel oil. It is used to produce precious stones, incandescent lamps, forge and weld metal products under the influence of an oxygen-hydrogen flame.

Liquid

Hydrogen(lat. Hydrogenium; denoted by the symbol H) - the first element of the periodic table of elements. Widely distributed in nature. The cation (and nucleus) of the most abundant hydrogen isotope, 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).

Simple substance hydrogen - H 2 - light colorless gas. It is flammable and explosive when mixed with air or oxygen. Non-toxic. Let's dissolve in ethanol and a number of metals: iron, nickel, palladium, platinum.

History

The release of combustible gas during the interaction of acids and metals was observed in the XVI and XVII centuries at the dawn of the formation of chemistry as a science. Mikhail Vasilyevich Lomonosov also directly pointed to its separation, but already definitely realizing that it was not phlogiston. The English physicist and chemist Henry Cavendish investigated 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 correct conclusions. The French chemist Antoine Lavoisier, together with the engineer J. Meunier, using special gas meters, in 1783 synthesized water, and then analyzed it, decomposing water vapor with red-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.

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 taken together 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 differ significantly in size, density and temperature.

Earth's crust and living organisms

Mass fraction of hydrogen in earth crust is 1% - this is the tenth most common element. However, its role in nature is determined not by mass, but by the number of atoms, the proportion of which among other elements is 17% (second place after oxygen, the proportion of atoms of which is ~ 52%). Therefore, the importance of hydrogen in the chemical processes taking place on Earth is almost as great as oxygen. Unlike oxygen, which exists on Earth in both bound and free states, practically 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 a 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.

Receiving

Industrial methods for obtaining simple substances depend on the form in which the corresponding element is found in nature, that is, what can be the raw materials for its production. So, oxygen, available in a free state, is obtained by a physical method - by separation from liquid air. Almost all hydrogen is in the form of compounds, therefore, to obtain it, they use chemical methods... In particular, decomposition reactions can be used. One of the methods for producing hydrogen is the reaction of water decomposition by electric current.

The main industrial method for producing hydrogen is the reaction of methane with water, which is part of natural gas. It is carried out at high temperature(it is easy to make sure that when methane is passed 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, it is not necessary to use natural raw materials, but to select those starting substances from which it is easier to isolate the required substance. For example, in a laboratory, oxygen is not obtained from the air. The same applies to the production of hydrogen. One of laboratory methods the production of hydrogen, which is sometimes used in industry, is the decomposition of water by electric current.

Usually in the laboratory, hydrogen is produced by the interaction of zinc with hydrochloric acid.

In industry

1.Electrolysis of aqueous solutions of salts:

2NaCl + 2H 2 O → H 2 + 2NaOH + Cl 2

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

H 2 O + C? H 2 + 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 + 4H 2

4. Cracking and reforming of hydrocarbons in the process of oil refining.

In the laboratory

1.The action of dilute acids on metals. To carry out such a 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.The action of alkalis on zinc or aluminum:

2Al + 2NaOH + 6H 2 O → 2Na + 3H 2

Zn + 2KOH + 2H 2 O → K 2 + H 2

5.By electrolysis. During the electrolysis of aqueous solutions of alkalis or acids, hydrogen is evolved 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. Orthohydrogen molecule o-H 2 (m.p. -259.10 ° C, bp. -252.56 ° C) nuclear spins are directed in the same way (parallel), p-H 2 (m.p. -259.32 ° C, bp. -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-H 2.

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 entirely 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 equilibrium at room temperature is formed (ortho-pair: 75:25). Without a catalyst, the transformation occurs slowly (under conditions of the interstellar medium - with characteristic times up to cosmological), which makes it possible to study the properties of individual modifications.

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

The hydrogen molecule is diatomic - Н 2. Under normal conditions, it is a colorless, odorless and tasteless gas. Density 0.08987 g / l (n.u.), 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 readily 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 associated with its ability to diffuse through them; diffusion through a carbonaceous alloy (for example, steel) is sometimes accompanied by the destruction of the alloy due to the interaction of hydrogen with carbon (the 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 / cm 3) and fluid (viscosity at -253 ° C 13.8 cpoise). The critical parameters of hydrogen are very low: the temperature is −240.2 ° C and the pressure is 12.8 atm. This explains the difficulties in liquefying hydrogen. In the liquid state, equilibrium hydrogen consists of 99.79% para-H 2, 0.21% ortho-H 2.

Solid hydrogen, melting point -259.2 ° C, density 0.0807 g / cm 3 (at -262 ° C) - snow-like mass, crystals of hexagonal system, 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, respectively, 99.9885 ± 0.0070% and 0.0115 ± 0.0070%. This ratio may vary slightly depending on the source and method of producing hydrogen.

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

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

Natural hydrogen consists of H 2 and HD (hydrogen deuteride) 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 point, K / kPa	Critical point, 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. Heteroisotopic hydrogen (HD, HT, DT) have no ortho and para modifications.

Chemical properties

Fraction of dissociated hydrogen molecules

The hydrogen molecules H 2 are quite strong, and a lot of energy must be expended in order for hydrogen to react:

H 2 = 2H - 432 kJ

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

Ca + H 2 = CaH 2

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

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

О 2 + 2Н 2 = 2Н 2 О

It can “take” 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 proceeds with an explosion in the dark and at any temperature,

Cl 2 + H 2 → 2HCl, the reaction proceeds with an explosion, only in the light.

Reacts with soot under strong heating:

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- salty, 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 reduction 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 (e.g. Wilkinson's catalyst) or heterogeneous (e.g. Raney nickel, palladium-carbon).

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

Hydrogen Geochemistry

Free hydrogen H 2 is relatively rare in terrestrial gases, but in the form of water it plays an extremely important role in geochemical processes.

Hydrogen can be part of minerals in the form of ammonium ion, hydroxyl ion and crystal water.

In the atmosphere, hydrogen is continuously formed as a result of the decomposition of water by solar radiation. Having a small mass, hydrogen molecules have a high speed of diffusion movement (it is close to the second cosmic speed) and, falling into the upper layers of the atmosphere, can fly into space.

Features of treatment

When mixed with air, hydrogen forms an explosive mixture - the so-called explosive 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 the air contains about 21% oxygen. Also hydrogen is fire hazardous. Liquid hydrogen can cause severe frostbite if it comes into contact with the skin.

Explosive concentrations of hydrogen with 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-scale wholesale supplies fluctuates in the range of $ 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 food additive E949(packing gas)

Food industry

Aviation industry

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

Fuel

Hydrogen is used as propellant.

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

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

"Liquid hydrogen"("LH") is a liquid aggregate state of hydrogen, with a low specific gravity 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 the state of aggregation to gaseous is 848: 1 at 20 ° C.

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

History

The first documented use of artificial cooling in 1756 was carried out by the English scientist William Cullen, Gaspard Monge was the first to obtain the 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 a 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 the cascade Joule-Thomson expansion effect and regenerative cooling in 1876. In 1885, the Polish physicist and chemist Zygmund Wrobblewski published a critical temperature of 33 K for hydrogen and a critical pressure of 13.3 atm. and a boiling point at 23 K. Hydrogen was first liquefied by James Dewar in 1898 using regenerative refrigeration and his invention, the Dewar flask. The first synthesis of the stable isomer of liquid hydrogen - parahydrogen - was carried out by Paul Hartek and Karl Bonhoeffer in 1929.

Spin isomers of hydrogen

Hydrogen at room temperature consists mainly of the spin isomer, orthohydrogen. After production, liquid hydrogen is in a metastable state and must be converted to a parahydrogenic form in order to avoid the explosive exothermic reaction that occurs when it changes at low temperatures. Conversion to the parahydrogen phase is usually performed using catalysts such as iron oxide, chromium oxide, activated carbon, platinum-coated asbestos, rare earth metals, or by using 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 structures, the creators of the equipment on "ZhV" can use or only modify systems using liquefied natural gas ("LNG"). However, due to the lower bulk energy density, combustion requires a higher volume of hydrogen than natural gas. If liquid hydrogen is used instead of "CNG" in reciprocating engines, a more cumbersome fuel system is usually required. With direct injection, the increased intake losses reduce the cylinder filling.

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

Advantages

The advantage of using hydrogen is the "zero emission" 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 respect to liquid oxygen, but requires more caution due to the fire hazard. Even with thermally insulated containers, it is difficult to keep it at the low temperature required to keep it liquid (it usually evaporates at a rate of 1% per day). When handling it, you must also 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 that is used for jet acceleration of launch vehicles and spacecraft... In most hydrogen-fueled liquid propellant rocket engines, it is first used to regeneratively cool the nozzle and other parts of the engine, before it is mixed with an oxidizer and burned to produce thrust. Used modern H 2 / O 2 engines consume a re-enriched fuel mixture, which results in some unburned hydrogen in the exhaust. In addition to increasing the specific impulse of the engine by reducing the molecular weight, it further reduces the 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. For 2009, there is only one launch vehicle (LV "Delta-4"), 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 on 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 slushy hydrogen, that is, the semi-frozen form of "ZhV".

Lecture 29

Hydrogen. Water

Lecture plan:

Water. Chemical and physical properties

The role of hydrogen and water in nature

Hydrogen as a chemical element

Hydrogen is the only element of DI Mendeleev's periodic table, the location of which is ambiguous. His chemical symbol recorded twice in the periodic table: in both IA and VIIA groups. This is due to the fact that hydrogen has a number of properties that unite it as with alkali metals and with halogens (Table 14).

Table 14

Comparison of the properties of hydrogen with the properties of alkali metals and halogens

Similarity to alkali metals	Similarity to halogens
On the outside energy level hydrogen atoms contain one electron. Hydrogen belongs to s-elements	Until the completion of the outer and only level, hydrogen atoms, like halogen atoms, lack one electron
Hydrogen exhibits reducing properties. As a result of oxidation, hydrogen obtains the oxidation state +1, which is most often found in its compounds.	Hydrogen, like halogens, in compounds with alkali and alkaline earth metals has an oxidation state of -1, which confirms its oxidizing properties.
The presence in space of solid hydrogen with a metal crystal lattice is assumed.	Like fluorine and chlorine, hydrogen is a gas under normal conditions. Its molecules, like halogen molecules, are diatomic and formed due to a covalent non-polar bond

In nature, hydrogen exists in the form of three isotopes with mass numbers 1, 2 and 3: protium 1 1 H, deuterium 2 1 D and tritium 3 1 T. The first two are stable isotopes, and the third is radioactive. The natural mixture of isotopes is dominated by protium. The quantitative ratios between the isotopes H: D: T are 1: 1.46 10 -5: 4.00 10 -15.

Compounds of hydrogen isotopes differ in properties from each other. So, for example, the boiling point and freezing point of light protium water (H 2 O) are, respectively, equal to - 100 о С and 0 о С, and deuterium (D 2 O) - 101.4 о С and 3.8 о С. involving light water is higher than heavy water.

In the Universe, hydrogen is the most abundant element - it accounts for about 75% of the mass of the Universe or over 90% of all its atoms. Hydrogen is a part of water in its most important geological shell of the Earth - the hydrosphere.

Hydrogen forms, along with carbon, all organic substances, that is, it is part of the living shell of the Earth - the biosphere. In the earth's crust - the lithosphere - the mass content of hydrogen is only 0.88%, that is, it takes 9th place among all elements. Air shell of the Earth - the atmosphere contains less than a millionth part of the total volume, attributable to molecular hydrogen. It is found only in the upper atmosphere.

Production and use of hydrogen

For the first time, hydrogen was obtained in the 16th century by the medieval physician and alchemist Paracelsus, when an iron plate was immersed in sulfuric acid, and in 1766 the English chemist Henry Cavendish proved that hydrogen is obtained not only by the interaction of iron with sulfuric acid, but also other metals with other acids. Cavendish also described for the first time the properties of hydrogen.

V laboratory hydrogen conditions are obtained:

1. Interaction of metals with acid:

Zn + 2HCl → ZnCl 2 + H 2

2. Interaction of alkali and alkaline earth metals with water

2Na + 2H 2 O → 2NaOH + H 2

Ca + 2H 2 O → Ca (OH) 2 + H 2

V industry hydrogen is obtained in the following ways:

1. Electrolysis of aqueous solutions of salts, acids and alkalis. Most often used solution table salt:

2NaCl + 2H 2 O → el. current H 2 + Cl 2 + NaOH

2. Recovery of water vapor with hot coke:

С + Н 2 О → t СО + Н 2

The resulting mixture of carbon monoxide and hydrogen is called water gas (synthesis gas), and is widely used for the synthesis of various chemical products (ammonia, methanol, etc.). To extract hydrogen from water gas, carbon monoxide is converted into carbon dioxide, when heated with water vapor:

CO + H 2 → t CO 2 + H 2

3. Heating methane in the presence of water vapor and oxygen. This method is currently the main one:

2СН 4 + О 2 + 2Н 2 О → t 2СО 2 + 6Н 2

Hydrogen is widely used for:

1.industrial synthesis of ammonia and hydrogen chloride;

2. production of methanol and synthetic liquid fuel in the composition of synthesis gas (2 volumes of hydrogen and 1 volume of CO);

3. hydrotreating and hydrocracking of petroleum fractions;

4. hydrogenation of liquid fats;

5. cutting and welding of metals;

6. obtaining tungsten, molybdenum and rhenium from their oxides;

7. space engines as fuel.

8. In thermonuclear reactors, hydrogen isotopes are used as fuel.

Physical and chemical properties of hydrogen

Hydrogen is a colorless, tasteless and odorless gas. Density at n.u. 0.09 g / l (14 times lighter than air). Hydrogen is poorly soluble in water (only 2 volumes of gas per 100 volumes of water), but it is well absorbed by d-metals - nickel, platinum, palladium (up to 900 volumes of hydrogen dissolves in one volume of palladium).

V chemical reactions hydrogen exhibits both reducing and oxidizing properties. Most often, hydrogen acts as a reducing agent.

1. Interaction with non-metals... Hydrogen forms volatile hydrogen compounds with non-metals (see Lecture 25).

With halogens the reaction rate and the conditions of the course change from fluorine to iodine: hydrogen reacts with fluorine with an explosion even in the dark, with chlorine the reaction proceeds quite calmly with a slight irradiation with light, with bromine and iodine the reactions are reversible and proceed only when heated:

H 2 + F 2 → 2HF

H 2 + Cl 2 → hν 2HCl

H 2 + I 2 → t 2HI

With oxygen and with sulfur, hydrogen reacts with slight heating. A mixture of oxygen and hydrogen in a 1: 2 ratio is called oxyhydrogen gas:

Н 2 + О 2 → t Н 2 О

H 2 + S → t H 2 S

With nitrogen, phosphorus and carbon the reaction takes place under heating, at elevated pressure and in the presence of a catalyst. The reactions are reversible:

3H 2 + N 2 → cat., P, t2NH 3

2H 2 + 3P → cat., P, t3PH 3

H 2 + C → cat., P, t CH 4

2. Interaction with complex substances. At high temperatures, hydrogen reduces metals from their oxides:

CuO + H 2 → t Cu + H 2 O

3. At interaction with alkaline and alkaline earth metals hydrogen exhibits oxidizing properties:

2Na + H 2 → 2NaH

Ca + H 2 → CaH 2

4. Interaction with organic matter. Hydrogen actively interacts with many organic substances, such reactions are called hydrogenation reactions. Such reactions will be discussed in more detail in the III part of the collection "Organic chemistry".