History of the discovery of hydrogen

If it is the most common chemical element on Earth, then hydrogen is the most common element in the entire Universe. Ours (and other stars) consists of about half hydrogen, and as for interstellar gas, it consists of 90% hydrogen atoms. This chemical element also occupies a significant place on Earth, because together with oxygen it is part of water, and its very name “hydrogen” comes from two ancient Greek words: “water” and “giving birth”. In addition to water, hydrogen is present in most organic matter and cells, without it, as without oxygen, Life itself would be unthinkable.

History of the discovery of hydrogen

The first among scientists to notice hydrogen was the great alchemist and physician of the Middle Ages, Theophrastus Paracelsus. In his alchemical experiments, in the hope of finding the “philosopher’s stone,” by mixing with acids, Paracelsus obtained some previously unknown flammable gas. True, it was never possible to separate this gas from the air.

Only a century and a half after Paracelsus, the French chemist Lemery managed to separate hydrogen from air and prove its flammability. True, Lemery never realized that the gas he obtained was pure hydrogen. In parallel, the Russian scientist Lomonosov was also engaged in similar chemical experiments, but the real breakthrough in the study of hydrogen was made by the English chemist Henry Cavendish, who is rightfully considered the discoverer of hydrogen.

In 1766, Cavendish succeeded in obtaining pure hydrogen, which he called “combustible air.” Another 20 years later, the talented French chemist Antoine Lavoisier was able to synthesize water and isolate from it this very “flammable air” - hydrogen. And by the way, it was Lavoisier who suggested hydrogen its name - “Hydrogenium”, also known as “hydrogen”.

Antoine Lavoisier with his wife, who helped him conduct chemical experiments, including the synthesis of hydrogen.

At the heart of the arrangement chemical elements V periodic table Mendeleev's atomic weight is calculated relative to the atomic weight of hydrogen. That is, in other words, hydrogen and its atomic weight is the cornerstone of the periodic table, the fulcrum on the basis of which the great chemist created his system. Therefore, it is not surprising that hydrogen occupies an honorable first place in the periodic table.

In addition, hydrogen has the following characteristics:

• The atomic mass of hydrogen is 1.00795.
• Hydrogen has three isotopes, each of which has individual properties.
• Hydrogen is a light element with low density.
• Hydrogen has reducing and oxidizing properties.
• When it comes into contact with metals, hydrogen accepts their electron and becomes an oxidizing agent. Such compounds are called hydrates.

Hydrogen is a gas; its molecule consists of two atoms.

This is what a hydrogen molecule looks like schematically.

Molecular hydrogen, formed from such diatomic molecules, explodes when brought to a burning match. During an explosion, a hydrogen molecule breaks down into atoms, which turn into helium nuclei. This is exactly what happens on the Sun and other stars - due to the constant disintegration of hydrogen molecules, our star burns and warms us with its heat.

Physical properties of hydrogen

Hydrogen has the following physical properties:

• The boiling point of hydrogen is 252.76 °C;
• And at a temperature of 259.14 °C it already begins to melt.
• Hydrogen is slightly soluble in water.
• Pure hydrogen is a very dangerous explosive and flammable substance.
• Hydrogen is 14.5 times lighter than air.

Chemical properties of hydrogen

Since hydrogen can be in different situations Both an oxidizing agent and a reducing agent, it is used to carry out reactions and syntheses.

The oxidizing properties of hydrogen interact with active (usually alkali and alkaline earth) metals, the result of these interactions is the formation of hydrides - salt-like compounds. However, hydrides are also formed during the reactions of hydrogen with low-reactive metals.

The reducing properties of hydrogen have the ability to reduce metals to simple substances from their oxides, in the industry this is called hydrogenothermy.

How to get hydrogen?

Among the industrial means of producing hydrogen are:

• coal gasification,
• steam reforming of methane,
• electrolysis.

In the laboratory, hydrogen can be obtained:

• during the hydrolysis of metal hydrides,
• when alkali and alkaline earth metals react with water,
• when dilute acids interact with active metals.

Applications of hydrogen

Since hydrogen is 14 times lighter than air, it old times they were stuffed with Balloons and airships. But after a series of disasters that occurred with airships, designers had to look for a replacement for hydrogen (remember, pure hydrogen is an explosive substance, and the slightest spark was enough to cause an explosion).

The explosion of the Hindenburg airship in 1937, the cause of the explosion was precisely the ignition of hydrogen (due to a short circuit) on which this huge airship was flying.

Therefore, for similar aircraft instead of hydrogen, they began to use helium, which is also lighter than air; obtaining helium is more labor-intensive, but it is not as explosive as hydrogen.

Hydrogen is also used for cleaning various types fuels, especially those based on oil and petroleum products.

Hydrogen, video

And finally, an educational video on the topic of our article.

Characteristics of s-elements

The block of s-elements includes 13 elements, common to which is the building of an external energy level in their s-sublevel atoms.

Although hydrogen and helium are classified as s-elements, due to the specific nature of their properties, they should be considered separately. Hydrogen, sodium, potassium, magnesium, calcium are vital elements.

Compounds of s-elements exhibit general patterns in properties, which is explained by the similarity electronic structure their atoms. All outer electrons are valence electrons and take part in the formation chemical bonds. That's why maximum degree the oxidation of these elements in compounds is equal to number electrons in the outer layer and is accordingly equal to the number of the group in which the element is located. The oxidation state of s-element metals is always positive. Another feature is that after the electrons of the outer layer are separated, an ion with a noble gas shell remains. As the atomic number of an element or atomic radius increases, the ionization energy decreases (from 5.39 eV y Li to 3.83 eV y Fr), and the reduction activity of the elements increases.

The vast majority of compounds of s-elements are colorless (unlike compounds of d-elements), since the transition of d-electrons from low energy levels to higher energy levels, which causes color, is excluded.

Compounds of elements of groups IA - IIA are typical salts; in an aqueous solution they almost completely dissociate into ions and are not subject to cation hydrolysis (except for Be 2+ and Mg 2+ salts).

hydrogen hydride ionic covalent

Complexation is not typical for s-element ions. Crystalline complexes of s - elements with ligands H 2 O-crystalline hydrates have been known since ancient times, for example: Na 2 B 4 O 7 10H 2 O-borax, KAl (SO 4) 2 12H 2 O-alum. Water molecules in crystalline hydrates are grouped around the cation, but sometimes completely surround the anion. Due to the small ion charge and large ion radius, alkali metals are least prone to forming complexes, including aqua complexes. As complexing agents in complex compounds Lithium, beryllium, and magnesium ions are of low stability.

Hydrogen. Chemical properties of hydrogen

Hydrogen is the lightest s-element. His electronic configuration in the ground state 1S 1. A hydrogen atom consists of one proton and one electron. The peculiarity of hydrogen is that its valence electron is located directly in the sphere of action atomic nucleus. Hydrogen does not have an intermediate electron layer, so hydrogen cannot be considered an electronic analogue of alkali metals.

Like alkali metals, hydrogen is a reducing agent and exhibits an oxidation state of +1. The spectra of hydrogen are similar to the spectra of alkali metals. What makes hydrogen similar to alkali metals is its ability to produce a hydrated, positively charged H + ion in solutions.

Like a halogen, the hydrogen atom is missing one electron. This determines the existence of the hydride ion H - .

In addition, like halogen atoms, hydrogen atoms are characterized by a high ionization energy (1312 kJ/mol). Thus, hydrogen occupies a special position in the Periodic Table of Elements.

Hydrogen is the most abundant element in the universe, accounting for up to half the mass of the sun and most stars.

On the sun and other planets, hydrogen is in the atomic state, in the interstellar medium in the form of partially ionized diatomic molecules.

Hydrogen has three isotopes; protium 1 H, deuterium 2 D and tritium 3 T, and tritium is a radioactive isotope.

Hydrogen molecules are distinguished by high strength and low polarizability, small size and low mass, and have high mobility. Therefore, hydrogen has very low melting points (-259.2 o C) and boiling points (-252.8 o C). Due to the high dissociation energy (436 kJ/mol), the disintegration of molecules into atoms occurs at temperatures above 2000 o C. Hydrogen is a colorless gas, odorless and tasteless. It has a low density - 8.99·10 -5 g/cm At very high pressures, hydrogen transforms into a metallic state. It is believed that on distant planets solar system- On Jupiter and Saturn, hydrogen is in a metallic state. There is an assumption that the composition of the earth's core also includes metallic hydrogen, where it is found at ultra-high pressure created by the earth's mantle.

Chemical properties. At room temperature, molecular hydrogen reacts only with fluorine, when irradiated with light - with chlorine and bromine, and when heated with O 2, S, Se, N 2, C, I 2.

Reactions of hydrogen with oxygen and halogens proceed by a radical mechanism.

Interaction with chlorine is an example of an unbranched reaction when irradiated with light (photochemical activation) or when heated (thermal activation).

Сl+ H2 = HCl + H (chain development)

H+ Cl 2 = HCl + Cl

The explosion of a detonating gas - a hydrogen-oxygen mixture - is an example of a branched chain process, when the initiation of the chain includes not one, but several stages:

H 2 + O 2 = 2OH

H+ O 2 = OH+O

O+ H 2 = OH+ H

OH + H 2 = H 2 O + H

An explosion process can be avoided if you work with pure hydrogen.

Since hydrogen is characterized by a positive (+1) and negative (-1) oxidation state, hydrogen can exhibit both reducing and oxidizing properties.

The reducing properties of hydrogen manifest themselves when interacting with non-metals:

H 2 (g) + Cl 2 (g) = 2HCl (g),

2H 2 (g) + O 2 (g) = 2H 2 O (g),

These reactions proceed with the release large quantity heat, which indicates the high energy (strength) of the H-Cl, H-O bonds. Therefore, hydrogen exhibits reducing properties towards many oxides and halides, for example:

This is the basis for the use of hydrogen as a reducing agent for the production of simple substances from halide oxides.

An even stronger reducing agent is atomic hydrogen. It is formed from a molecular electron discharge under low pressure conditions.

Hydrogen has a high reducing activity at the moment of release during the interaction of a metal with an acid. This hydrogen reduces CrCl 3 to CrCl 2:

2CrCl 3 + 2HCl + 2Zn = 2CrCl 2 + 2ZnCl 2 +H 2 ^

The interaction of hydrogen with nitrogen oxide (II) is important:

2NO + 2H2 = N2 + H2O

Used in purification systems for the production of nitric acid.

As an oxidizing agent, hydrogen interacts with active metals:

In this case, hydrogen behaves like a halogen, forming similar to halides hydrides.

Hydrides of s-elements of group I have an ionic structure of the NaCl type. Chemically, ionic hydrides behave like basic compounds.

Covalent hydrides include hydrides of non-metallic elements that are less electronegative than hydrogen itself, for example, hydrides of the composition SiH 4, BH 3, CH 4. By chemical nature, non-metal hydrides are acidic compounds.

A characteristic feature of the hydrolysis of hydrides is the release of hydrogen; the reaction proceeds via a redox mechanism.

Basic hydride

Acid hydride

Due to the release of hydrogen, hydrolysis proceeds completely and irreversibly (?H<0, ?S>0). In this case, basic hydrides form an alkali, and acidic hydrides form an acid.

The standard potential of the system is B. Therefore, the H ion is a strong reducing agent.

In the laboratory, hydrogen is produced by reacting zinc with 20% sulfuric acid in a Kipp apparatus.

Technical zinc often contains small impurities of arsenic and antimony, which are reduced by hydrogen at the time of release to poisonous gases: arsine SbH 3 and stabine SbH This hydrogen can poison you. With chemically pure zinc, the reaction proceeds slowly due to overvoltage and a good current of hydrogen cannot be obtained. The rate of this reaction is increased by adding crystals of copper sulfate; the reaction is accelerated by the formation of a Cu-Zn galvanic couple.

More pure hydrogen is formed by the action of alkali on silicon or aluminum when heated:

In industry, pure hydrogen is produced by electrolysis of water containing electrolytes (Na 2 SO 4, Ba (OH) 2).

A large amount of hydrogen is produced as a by-product during the electrolysis of an aqueous sodium chloride solution with a diaphragm separating the cathode and anode spaces,

The largest amount of hydrogen is obtained by gasification of solid fuel (anthracite) with superheated water steam:

Or by conversion of natural gas (methane) with superheated steam:

The resulting mixture (synthesis gas) is used in the production of many organic compounds. The yield of hydrogen can be increased by passing synthesis gas over the catalyst, which converts CO into CO 2 .

Application. A large amount of hydrogen is consumed in the synthesis of ammonia. To obtain hydrogen chloride and of hydrochloric acid, for hydrogenation of vegetable fats, for the recovery of metals (Mo, W, Fe) from oxides. Hydrogen-oxygen flame is used for welding, cutting and melting metals.

Liquid hydrogen is used as rocket fuel. Hydrogen fuel is environmentally friendly and more energy-intensive than gasoline, so in the future it can replace petroleum products. Already, several hundred cars in the world are powered by hydrogen. The problems of hydrogen energy are related to the storage and transportation of hydrogen. Hydrogen stored in underground tankers in liquid state under a pressure of 100 atm. Transporting large quantities of liquid hydrogen poses serious risks.

MINSK COLLEGE OF TECHNOLOGY AND DESIGN OF LIGHT INDUSTRY

Essay

discipline: Chemistry

Topic: “Hydrogen and its compounds”

Prepared by: 1st year student 343 groups

Viskup Elena

Checked: Alyabyeva N.V.

Minsk 2009

The structure of the hydrogen atom in the periodic table

Oxidation states

Prevalence in nature

Hydrogen as a simple substance

Hydrogen compounds

Bibliography

The structure of the hydrogen atom in the periodic table

The first element of the periodic table (1st period, serial number 1). It does not have complete analogy with other chemical elements and does not belong to any group, therefore in the tables it is conditionally placed in group IA and/or group VIIA.

The hydrogen atom is the smallest and lightest of the atoms of all elements. The electronic formula of the atom is 1s 1. The usual form of existence of an element in a free state is a diatomic molecule.

Oxidation states

The hydrogen atom in compounds with more electronegative elements exhibits an oxidation state of +1, for example HF, H 2 O, etc. And in compounds with metal hydrides, the oxidation state of the hydrogen atom is -1, for example NaH, CaH 2, etc. It has an electronegativity value intermediate between typical metals and non-metals. Capable of catalytically reducing in organic solvents such as acetic acid or alcohol, many organic compounds: unsaturated compounds to saturated ones, some sodium compounds to ammonia or amines.

Prevalence in nature

Natural hydrogen consists of two stable isotopes - protium 1 H, deuterium 2 H and tritium 3 H. Deuterium is otherwise designated as D, and tritium as T. Various combinations are possible, for example NT, HD, TD, H 2, D 2, T2. Hydrogen is more common in nature in the form of various compounds with sulfur (H 2 S), oxygen (in the form of water), carbon, nitrogen and chlorine. Less often in the form of compounds with phosphorus, iodine, bromine and other elements. It is part of all plant and animal organisms, oil, fossil coals, natural gas, a number of minerals and rocks. In a free state, it is found very rarely in small quantities - in volcanic gases and decomposition products of organic residues. Hydrogen is the most abundant element in the Universe (about 75%). It is a constituent of the Sun and most stars, as well as the planets Jupiter and Saturn, which are mainly composed of hydrogen. On some planets, hydrogen can exist in solid form.

Hydrogen as a simple substance

A hydrogen molecule consists of two atoms connected by a covalent nonpolar bond. Physical properties- gas without color and odor. It spreads faster than other gases in space, passes through small pores, and at high temperatures penetrates steel and other materials relatively easily. Has high thermal conductivity.

Chemical properties. In its normal state at low temperatures it is inactive; it reacts with fluorine and chlorine without heating (in the presence of light).

H 2 + F 2 2HF H 2 +Cl 2 hv 2HCl

It interacts more actively with non-metals than with metals.

When interacting with various substances, it can exhibit both oxidizing and reducing properties.

Hydrogen compounds

One of the hydrogen compounds is halogens. They are formed when hydrogen combines with Group VIIA elements. HF, HCl, HBr and HI are colorless gases, highly soluble in water.

Cl 2 + H 2 OHClO + HCl; HClO-chlorine water

Since HBr and HI are typical reducing agents, they cannot be obtained by an exchange reaction like HCl.

CaF 2 + H 2 SO 4 = CaSO 4 + 2HF

Water is the most common hydrogen compound in nature.

2H 2 + O 2 = 2H 2 O

It has no color, no taste, no smell. A very weak electrolyte, but reacts actively with many metals and non-metals, basic and acidic oxides.

2H 2 O + 2Na = 2NaOH + H 2

H 2 O + BaO = Ba(OH) 2

3H 2 O + P 2 O 5 = 2H 3 PO 4

Heavy water (D 2 O) is an isotopic variety of water. The solubility of substances in heavy water is much less than in ordinary water. Heavy water is poisonous because it slows down biological processes in living organisms. Accumulates in the electrolysis residue during repeated electrolysis of water. Used as a coolant and neutron moderator in nuclear reactors.

Hydrides are the interaction of hydrogen with metals (at high temperatures) or non-metals less electronegative than hydrogen.

Si + 2H 2 = SiH 4

Hydrogen itself was discovered in the first half of the 16th century. Paracelsus. In 1776, G. Cavendish first investigated its properties; in 1783-1787, A. Lavoisier showed that hydrogen is part of water, included it in the list of chemical elements and proposed the name “hydrogen”.

Bibliography

1. M.B. Volovich, O.F. Kabardin, R.A. Lidin, L.Yu. Alikberova, V.S. Rokhlov, V.B. Pyatunin, Yu.A. Simagin, S.V. Simonovich/Schoolchildren’s Handbook/Moscow “AST-PRESS BOOK” 2003.

2. I.L. Knunyats / Chemical Encyclopedia / Moscow “Soviet Encyclopedia” 1988

3. I.E. Shimanovich / Chemistry 11 / Minsk “People's Asveta” 2008

4. F. Cotton, J. Wilkinson/Modern inorganic chemistry/ Moscow “Peace” 1969

Generalizing scheme "HYDROGEN"

I. Hydrogen is a chemical element

a) Position in PSHE

• serial number No. 1
• period 1
• group I (main subgroup “A”)
• relative mass Ar(H)=1
• Latin name Hydrogenium (giving birth to water)

b) The prevalence of hydrogen in nature

Hydrogen is a chemical element.	IN earth's crust (lithosphere and hydrosphere) – 1% by weight (10th place among all elements)
	ATMOSPHERE - 0.0001% by number of atoms
	The most common element in the universe – 92% of all atoms (main component stars and interstellar gas)

Hydrogen is a chemical element	In connections	H 2 O - water(11% by weight)
		CH 4 – methane gas(25% by weight)
		Organic matter(oil, flammable natural gases and others) In animal and plant organisms(that is, in protein composition, nucleic acids, fats, carbohydrates and others) In the human body on average it contains about 7 kilograms of hydrogen.

c) Valence of hydrogen in compounds

II. Hydrogen is a simple substance (H 2)

Receipt

1. Laboratory (Kipp apparatus) A) Interaction of metals with acids: Zn+ 2HCl = ZnCl 2 + H 2 salt B) Interaction active metals with water: 2Na + 2H 2 O = 2NaOH + H 2 base

2. Industry · Electrolysis of water email current 2H 2 O =2H 2 + O 2 · From natural gas t,Ni CH 4 + 2H 2 O=4H 2 +CO 2

Finding hydrogen in nature.

Hydrogen is widespread in nature; its content in the earth's crust (lithosphere and hydrosphere) is 1% by mass and 16% by number of atoms. Hydrogen is part of the most common substance on Earth - water (11.19% of Hydrogen by mass), in the composition of compounds that make up coal, oil, natural gases, clays, as well as animal and plant organisms (that is, in the composition of proteins, nucleic acids , fats, carbohydrates and others). Hydrogen is extremely rare in its free state; 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 near-Earth space, Hydrogen in the form of a flow of protons forms the internal (“proton”) radiation belt of the Earth. In space, Hydrogen is the most abundant 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. Hydrogen is present in the atmosphere of a number of planets and in comets in the form of free H 2, methane CH 4, ammonia NH 3, water H 2 O, and radicals. In the form of a stream of protons, Hydrogen is part of the corpuscular radiation of the Sun and cosmic rays.

There are three isotopes of hydrogen:
a) light hydrogen - protium,
b) heavy hydrogen – deuterium (D),
c) superheavy hydrogen – tritium (T).

Tritium is an unstable (radioactive) isotope, so it is practically never found in nature. Deuterium is stable, but it is very small: 0.015% (of the mass of all terrestrial hydrogen).

Valence of hydrogen in compounds

In compounds, hydrogen exhibits valence I.

Physical properties of hydrogen

The simple substance hydrogen (H 2) is a gas, lighter than air, colorless, odorless, tasteless, boiling point = – 253 0 C, hydrogen is insoluble in water, flammable. Hydrogen can be collected by displacing air from a test tube or water. In this case, the test tube must be turned upside down.

Hydrogen production

In the laboratory, hydrogen is produced as a result of the reaction

Zn + H 2 SO 4 = ZnSO 4 + H 2.

Instead of zinc, you can use iron, aluminum and some other metals, and instead of sulfuric acid, you can use some other dilute acids. The resulting hydrogen is collected in a test tube by displacing water (see Fig. 10.2 b) or simply in an inverted flask (Fig. 10.2 a).

In industry, hydrogen is produced in large quantities from natural gas (mainly methane) by reacting it with water vapor at 800 °C in the presence of a nickel catalyst:

CH 4 + 2H 2 O = 4H 2 +CO 2 (t, Ni)

or treat coal at high temperature with water vapor:

2H 2 O + C = 2H 2 + CO 2. (t)

Pure hydrogen is obtained from water by decomposing it electric shock(subjecting to electrolysis):

2H 2 O = 2H 2 + O 2 (electrolysis).

Hydrogen H is the most common element in the Universe (about 75% by mass), and on Earth it is the ninth most abundant. The most important natural hydrogen compound is water.
Hydrogen ranks first in the periodic table (Z = 1). It has the simplest atomic structure: the nucleus of the atom is 1 proton, surrounded by electron cloud consisting of 1 electron.
Under some conditions, hydrogen exhibits metallic properties (donates an electron), while in others it exhibits nonmetallic properties (accepts an electron).
Hydrogen isotopes found in nature are: 1H - protium (the nucleus consists of one proton), 2H - deuterium (D - the nucleus consists of one proton and one neutron), 3H - tritium (T - the nucleus consists of one proton and two neutrons).

Simple substance hydrogen

A hydrogen molecule consists of two atoms connected by a covalent nonpolar bond.
Physical properties. Hydrogen is a colorless, odorless, tasteless, non-toxic gas. The hydrogen molecule is not polar. Therefore, the forces of intermolecular interaction in hydrogen gas are small. This is manifested in low boiling points (-252.6 0C) and melting points (-259.2 0C).
Hydrogen is lighter than air, D (by air) = 0.069; slightly soluble in water (2 volumes of H2 dissolve in 100 volumes of H2O). Therefore, hydrogen, when produced in the laboratory, can be collected by air or water displacement methods.

Hydrogen production

In the laboratory:

1.The effect of dilute acids on metals:
Zn +2HCl → ZnCl 2 +H 2

2. Interaction between alkaline and metals with water:
Ca +2H 2 O → Ca(OH) 2 +H 2

3. Hydrolysis of hydrides: metal hydrides are easily decomposed by water to form the corresponding alkali and hydrogen:
NaH +H 2 O → NaOH +H 2
CaH 2 + 2H 2 O = Ca(OH) 2 + 2H 2

4.The effect of alkalis on zinc or aluminum or silicon:
2Al +2NaOH +6H 2 O → 2Na +3H 2
Zn +2KOH +2H 2 O → K 2 +H 2
Si + 2NaOH + H 2 O → Na 2 SiO 3 + 2H 2

5. Electrolysis of water. To increase the electrical conductivity of water, an electrolyte is added to it, for example NaOH, H 2 SO 4 or Na 2 SO 4. 2 volumes of hydrogen are formed at the cathode, and 1 volume of oxygen at the anode.
2H 2 O → 2H 2 +O 2

Industrial production of hydrogen

1. Methane conversion with steam, Ni 800 °C (cheapest):
CH 4 + H 2 O → CO + 3 H 2
CO + H 2 O → CO 2 + H 2

In total:
CH 4 + 2 H 2 O → 4 H 2 + CO 2

2. Water vapor through hot coke at 1000 o C:
C + H 2 O → CO + H 2
CO +H 2 O → CO 2 + H 2

The resulting carbon monoxide (IV) is absorbed by water, and 50% of industrial hydrogen is produced in this way.

3. By heating methane to 350°C in the presence of an iron or nickel catalyst:
CH 4 → C + 2H 2

4. Electrolysis aqueous solutions KCl or NaCl as a by-product:
2H 2 O + 2NaCl → Cl 2 + H 2 + 2NaOH

Chemical properties of hydrogen

• In compounds, hydrogen is always monovalent. It is characterized by an oxidation state of +1, but in metal hydrides it is equal to -1.
• The hydrogen molecule consists of two atoms. The emergence of a connection between them is explained by the formation of a generalized pair of electrons H:H or H 2
• Thanks to this generalization of electrons, the H 2 molecule is more energetically stable than its individual atoms. To break 1 mole of hydrogen molecules into atoms, it is necessary to expend 436 kJ of energy: H 2 = 2H, ∆H° = 436 kJ/mol
• This explains the relatively low activity of molecular hydrogen at ordinary temperatures.
• With many non-metals, hydrogen forms gaseous compounds such as RH 4, RH 3, RH 2, RH.

1) Forms hydrogen halides with halogens:
H 2 + Cl 2 → 2HCl.
At the same time, it explodes with fluorine, reacts with chlorine and bromine only when illuminated or heated, and with iodine only when heated.

2) With oxygen:
2H 2 + O 2 → 2H 2 O
with heat release. At normal temperatures the reaction proceeds slowly, above 550°C it explodes. A mixture of 2 volumes of H 2 and 1 volume of O 2 is called detonating gas.

3) When heated, it reacts vigorously with sulfur (much more difficult with selenium and tellurium):
H 2 + S → H 2 S (hydrogen sulfide),

4) With nitrogen with the formation of ammonia only on a catalyst and at elevated temperatures and pressures:
ZN 2 + N 2 → 2NH 3

5) With carbon at high temperatures:
2H 2 + C → CH 4 (methane)

6) Forms hydrides with alkali and alkaline earth metals (hydrogen is an oxidizing agent):
H 2 + 2Li → 2LiH
in metal hydrides, the hydrogen ion is negatively charged (oxidation state -1), that is, Na + H hydride - built similar to Na + Cl chloride -

With complex substances:

7) With metal oxides (used to reduce metals):
CuO + H 2 → Cu + H 2 O
Fe 3 O 4 + 4H 2 → 3Fe + 4H 2 O

8) with carbon monoxide (II):
CO + 2H 2 → CH 3 OH
Synthesis - gas (a mixture of hydrogen and carbon monoxide) is of important practical importance, because depending on temperature, pressure and catalyst, various organic compounds are formed, for example HCHO, CH 3 OH and others.

9) Unsaturated hydrocarbons react with hydrogen, becoming saturated:
C n H 2n + H 2 → C n H 2n+2.