The interaction of hydrogen with oxygen is a reaction. Chapter iv. simple and complex substances. hydrogen and oxygen. Why is hydrogen flammable

10.1 Hydrogen

The name "hydrogen" refers to both a chemical element and a simple substance. Element hydrogen is made up of hydrogen atoms. simple substance hydrogen is made up of hydrogen molecules.

a) Chemical element hydrogen

In the natural series of elements, the serial number of hydrogen is 1. In the system of elements, hydrogen is in the first period in the IA or VIIA group.

Hydrogen is one of the most abundant elements on Earth. The molar fraction of hydrogen atoms in the atmosphere, hydrosphere and lithosphere of the Earth (collectively, this is called the earth's crust) is 0.17. It is found in water, many minerals, oil, natural gas, plants and animals. The average human body contains about 7 kilograms of hydrogen.

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 practically does not occur in nature. Deuterium is stable, but there is very little of it: w D = 0.015% (of the mass of all terrestrial hydrogen). Therefore, the atomic mass of hydrogen differs very little from 1 Dn (1.00794 Dn).

b) Hydrogen atom

From previous sections course of chemistry, you already know the following characteristics of the hydrogen atom:

The valence capabilities of a hydrogen atom are determined by the presence of one electron in a single valence orbital. A large ionization energy makes the hydrogen atom not prone to donate an electron, and not too high an electron affinity leads to a slight tendency to accept it. Consequently, in chemical systems, the formation of the H cation is impossible, and compounds with the H anion are not very stable. Thus, the formation of a covalent bond with other atoms due to its one unpaired electron is most characteristic of the hydrogen atom. Both in the case of the formation of an anion and in the case of the formation of a covalent bond, the hydrogen atom is monovalent.
In a simple substance, the oxidation state of hydrogen atoms is zero, in most compounds hydrogen exhibits an oxidation state of +I, and only in hydrides of the least electronegative elements in hydrogen is an oxidation state of –I.
Information about the valence capabilities of the hydrogen atom is given in table 28. The valence state of a hydrogen atom connected by one covalent bond with any atom is indicated in the table by the symbol "H-".

Table 28Valence possibilities of the hydrogen atom

Valence state				Examples of chemicals
			I 0 –I	HCl, H 2 O, H 2 S, NH 3 , CH 4 , C 2 H 6 , NH 4 Cl, H 2 SO 4 , NaHCO 3 , KOH H2 B 2 H 6 , SiH 4 , GeH 4
				NaH, KH, CaH 2 , BaH 2

c) Hydrogen molecule

The diatomic hydrogen molecule H 2 is formed when hydrogen atoms are bound by the only covalent bond possible for them. Communication is formed by the exchange mechanism. According to the way electron clouds overlap, this is an s-bond (Fig. 10.1 A). Since the atoms are the same, the bond is non-polar.

Interatomic distance (more precisely, the equilibrium interatomic distance, because atoms vibrate) in a hydrogen molecule r(H-H) = 0.74 A (Fig. 10.1 V), which is much less than the sum of orbital radii (1.06 A). Consequently, the electron clouds of bonding atoms overlap deeply (Fig. 10.1 b), and the bond in the hydrogen molecule is strong. This is also evidenced by the rather large value of the binding energy (454 kJ/mol).
If we characterize the shape of the molecule by the boundary surface (similar to the boundary surface of the electron cloud), then we can say that the hydrogen molecule has the shape of a slightly deformed (elongated) ball (Fig. 10.1 G).

d) Hydrogen (substance)

Under normal conditions, hydrogen is a colorless and odorless gas. In not large quantities it is non-toxic. Solid hydrogen melts at 14 K (–259°C), while liquid hydrogen boils at 20 K (–253°C). Low melting and boiling points, a very small temperature interval for the existence of liquid hydrogen (only 6 °C), as well as small molar heats of melting (0.117 kJ/mol) and vaporization (0.903 kJ/mol) indicate that intermolecular bonds in hydrogen very weak.
Hydrogen density r (H 2) \u003d (2 g / mol): (22.4 l / mol) \u003d 0.0893 g / l. For comparison: the average air density is 1.29 g/l. That is, hydrogen is 14.5 times "lighter" than air. It is practically insoluble in water.
At room temperature hydrogen is inactive, but when heated, it reacts with many substances. In these reactions, hydrogen atoms can both increase and decrease their oxidation state: H 2 + 2 e- \u003d 2H -I, H 2 - 2 e- \u003d 2H + I.
In the first case, hydrogen is an oxidizing agent, for example, in reactions with sodium or calcium: 2Na + H 2 = 2NaH, ( t) Ca + H 2 = CaH 2 . ( t)
But the reducing properties are more characteristic of hydrogen: O 2 + 2H 2 \u003d 2H 2 O, ( t)
CuO + H 2 \u003d Cu + H 2 O. ( t)
When heated, hydrogen is oxidized not only by oxygen, but also by some other non-metals, such as fluorine, chlorine, sulfur, and even nitrogen.
In the laboratory, hydrogen is produced by the reaction

Zn + H 2 SO 4 \u003d ZnSO 4 + H 2.

Iron, aluminum and some other metals can be used instead of zinc, and some other dilute acids can be used instead of sulfuric acid. The resulting hydrogen is collected in a test tube by the method of water displacement (see Fig. 10.2 b) or simply into an inverted flask (Fig. 10.2 A).

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

CH 4 + 2H 2 O \u003d 4H 2 + CO 2 ( t, Ni)

or treated at high temperature with water vapor coal:

2H 2 O + C \u003d 2H 2 + CO 2. ( t)

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

2H 2 O \u003d 2H 2 + O 2 (electrolysis).

e) Hydrogen compounds

Hydrides (binary compounds containing hydrogen) are divided into two main types:
a) volatile (molecular) hydrides,
b) salt-like (ionic) hydrides.
Elements IVA - VIIA groups and boron form molecular hydrides. Of these, only hydrides of elements that form non-metals are stable:

B 2 H 6 ; CH 4 ; NH3; H2O; HF
SiH 4 ;PH 3 ; H2S; HCl
AsH 3 ; H2Se; HBr
H2Te; HI
With the exception of water, all of these compounds are gaseous substances at room temperature, hence their name - "volatile hydrides".
Some of the elements that form non-metals are also included in more complex hydrides. For example, carbon forms compounds with the general formulas C n H2 n+2 , C n H2 n, C n H2 n-2 and others, where n can be very large (organic chemistry studies these compounds).
Ionic hydrides include alkali, alkaline earth and magnesium hydrides. The crystals of these hydrides consist of H anions and metal cations in the highest oxidation state of Me or Me 2 (depending on the group of the system of elements).

LiH
NaH	MgH2
KH	CaH2
RbH	SrH 2
CSH	BaH2

Both ionic and almost all molecular hydrides (except H 2 O and HF) are reducing agents, but ionic hydrides exhibit reducing properties much stronger than molecular ones.
In addition to hydrides, hydrogen is a part of hydroxides and some salts. You will get acquainted with the properties of these more complex hydrogen compounds in the following chapters.
The main consumers of hydrogen produced in industry are plants for the production of ammonia and nitrogen fertilizers, where ammonia is obtained directly from nitrogen and hydrogen:

N 2 + 3H 2 2NH 3 ( R, t, Pt is the catalyst).

Hydrogen is used in large quantities to produce methyl alcohol (methanol) by the reaction 2H 2 + CO = CH 3 OH ( t, ZnO - catalyst), as well as in the production of hydrogen chloride, which is obtained directly from chlorine and hydrogen:

H 2 + Cl 2 \u003d 2HCl.

Sometimes hydrogen is used in metallurgy as a reducing agent in the production of pure metals, for example: Fe 2 O 3 + 3H 2 = 2Fe + 3H 2 O.

1. What particles do the nuclei of a) protium, b) deuterium, c) tritium consist of?
2. Compare the ionization energy of a hydrogen atom with the ionization energy of atoms of other elements. Which element is closest to hydrogen in this characteristic?
3. Do the same for the electron affinity energy
4. Compare the direction of polarization of the covalent bond and the degree of oxidation of hydrogen in the compounds: a) BeH 2 , CH 4 , NH 3 , H 2 O, HF; b) CH 4, SiH 4, GeH 4.
5. Write down the simplest, molecular, structural and spatial formula of hydrogen. Which one is the most commonly used?
6. They often say: "Hydrogen is lighter than air." What is meant by this? In what cases can this expression be taken literally, and in what cases not?
7. Make the structural formulas of potassium and calcium hydrides, as well as ammonia, hydrogen sulfide and hydrogen bromide.
8. Knowing the molar heats of fusion and vaporization of hydrogen, determine the values ​​of the corresponding specific quantities.
9. For each of the four reactions illustrating the basic chemical properties of hydrogen, make an electronic balance. List the oxidizing and reducing agents.
10. Determine the mass of zinc required to obtain 4.48 liters of hydrogen in a laboratory way.
11. Determine the mass and volume of hydrogen that can be obtained from 30 m 3 of a mixture of methane and water vapor, taken in a volume ratio of 1: 2, with a yield of 80%.
12. Make up the equations of the reactions that take place during the interaction of hydrogen a) with fluorine, b) with sulfur.
13. The reaction schemes below illustrate the basic chemical properties of ionic hydrides:

a) MH + O 2 MOH ( t); b) MH + Cl 2 MCl + HCl ( t);
c) MH + H 2 O MOH + H 2; d) MH + HCl(p) MCl + H 2
Here M is lithium, sodium, potassium, rubidium or cesium. Make up the equations of the corresponding reactions if M is sodium. Illustrate the chemical properties of calcium hydride with reaction equations.
14. Using the electron balance method, write the equations for the following reactions illustrating the reducing properties of some molecular hydrides:
a) HI + Cl 2 HCl + I 2 ( t); b) NH 3 + O 2 H 2 O + N 2 ( t); c) CH 4 + O 2 H 2 O + CO 2 ( t).

10.2 Oxygen

As in the case of hydrogen, the word "oxygen" is the name of both a chemical element and a simple substance. Except simple substance" oxygen"(dioxygen) the chemical element oxygen forms another simple substance called " ozone"(trioxygen). This allotropic modifications oxygen. The substance oxygen consists of oxygen molecules O 2 , and the substance ozone consists of ozone molecules O 3 .

a) The chemical element oxygen

In the natural series of elements, the serial number of oxygen is 8. In the system of elements, oxygen is in the second period in the VIA group.
Oxygen is the most abundant element on Earth. In the earth's crust, every second atom is an oxygen atom, that is, the molar fraction of oxygen in the atmosphere, hydrosphere and lithosphere of the Earth is about 50%. Oxygen (substance) - component air. The volume fraction of oxygen in the air is 21%. Oxygen (element) is a part of water, many minerals, as well as plants and animals. The human body contains an average of 43 kg of oxygen.
Natural oxygen consists of three isotopes (16 O, 17 O and 18 O), of which the lightest isotope 16 O is the most common. Therefore, the atomic mass of oxygen is close to 16 Dn (15.9994 Dn).

b) Oxygen atom

You know the following characteristics of the oxygen atom.

Table 29Valence possibilities of the oxygen atom

Valence state				Examples of chemicals
				Al 2 O 3 , Fe 2 O 3 , Cr 2 O 3 *
			-II –I 0 +I +II	H 2 O, SO 2, SO 3, CO 2, SiO 2, H 2 SO 4, HNO 2, HClO 4, COCl 2, H 2 O 2 O2** O 2 F 2 OF 2
				NaOH, KOH, Ca(OH) 2 , Ba(OH) 2 Na 2 O 2 , K 2 O 2 , CaO 2 , BaO 2
				Li 2 O, Na 2 O, MgO, CaO, BaO, FeO, La 2 O 3

* These oxides can also be considered as ionic compounds.
** The oxygen atoms in the molecule are not in the given valence state; this is just an example of a substance with an oxidation state of oxygen atoms equal to zero
A large ionization energy (like that of hydrogen) excludes the formation of a simple cation from the oxygen atom. The electron affinity energy is quite high (almost twice as high as that of hydrogen), which provides a greater propensity for the oxygen atom to attach electrons and the ability to form O 2A anions. But the electron affinity energy of the oxygen atom is still less than that of halogen atoms and even other elements of the VIA group. Therefore, oxygen anions ( oxide ions) exist only in compounds of oxygen with elements whose atoms donate electrons very easily.
By sharing two unpaired electrons, an oxygen atom can form two covalent bonds. Two lone pairs of electrons, due to the impossibility of excitation, can only enter into a donor-acceptor interaction. Thus, without taking into account the multiplicity of bonds and hybridization, the oxygen atom can be in one of the five valence states (Table 29).
The most characteristic of the oxygen atom is the valence state with W k \u003d 2, that is, the formation of two covalent bonds due to two unpaired electrons.
The very high electronegativity of the oxygen atom (only fluorine is higher) leads to the fact that in most of its compounds, oxygen has an oxidation state of -II. There are substances in which oxygen exhibits other values ​​of the oxidation state, some of them are given in table 29 as examples, and the comparative stability is shown in fig. 10.3.

c) Oxygen molecule

It has been experimentally established that the diatomic oxygen molecule O 2 contains two unpaired electrons. Using the method of valence bonds, such an electronic structure of this molecule cannot be explained. Nevertheless, the bond in the oxygen molecule is close in properties to the covalent bond. The oxygen molecule is non-polar. Interatomic distance ( r o–o = 1.21 A = 121 nm) is less than the distance between atoms connected by a single bond. The molar binding energy is rather high and amounts to 498 kJ/mol.

d) Oxygen (substance)

Under normal conditions, oxygen is a colorless and odorless gas. Solid oxygen melts at 55 K (–218 °C), while liquid oxygen boils at 90 K (–183 °C).
Intermolecular bonds in solid and liquid oxygen are somewhat stronger than in hydrogen, as evidenced by the larger temperature interval for the existence of liquid oxygen (36 ° C) and the molar heats of melting (0.446 kJ / mol) and vaporization (6. 83 kJ/mol).
Oxygen is slightly soluble in water: at 0 ° C, only 5 volumes of oxygen (gas!) dissolve in 100 volumes of water (liquid!)
The high propensity of oxygen atoms to attach electrons and high electronegativity lead to the fact that oxygen exhibits only oxidizing properties. These properties are especially pronounced when high temperature.
Oxygen reacts with many metals: 2Ca + O 2 = 2CaO, 3Fe + 2O 2 = Fe 3 O 4 ( t);
non-metals: C + O 2 \u003d CO 2, P 4 + 5O 2 \u003d P 4 O 10,
and complex substances: CH 4 + 2O 2 \u003d CO 2 + 2H 2 O, 2H 2 S + 3O 2 \u003d 2H 2 O + 2SO 2.

Most often, as a result of such reactions, various oxides are obtained (see Ch. II § 5), but active alkali metals, such as sodium, when burned, turn into peroxides:

2Na + O 2 \u003d Na 2 O 2.

Structural formula of the resulting sodium peroxide (Na) 2 (O-O).
A smoldering splinter placed in oxygen flares up. This is a convenient and easy way to detect pure oxygen.
In industry, oxygen is obtained from air by rectification (complex distillation), and in the laboratory, by subjecting some oxygen-containing compounds to thermal decomposition, for example:
2KMnO 4 \u003d K 2 MnO 4 + MnO 2 + O 2 (200 ° C);
2KClO 3 \u003d 2KCl + 3O 2 (150 ° C, MnO 2 - catalyst);
2KNO 3 \u003d 2KNO 2 + 3O 2 (400 ° C)
and, in addition, by catalytic decomposition of hydrogen peroxide at room temperature: 2H 2 O 2 = 2H 2 O + O 2 (MnO 2 -catalyst).
Pure oxygen is used in industry to intensify those processes in which oxidation occurs and to create a high-temperature flame. In rocket technology, liquid oxygen is used as an oxidizing agent.
Oxygen plays an important role in maintaining the life of plants, animals and humans. Under normal conditions, a person needs enough oxygen to breathe in the air. But in conditions where there is not enough air, or it is completely absent (in airplanes, during diving operations, in spaceships, etc.), special gas mixtures containing oxygen. Oxygen is also used in medicine for diseases that cause difficulty in breathing.

e) Ozone and its molecules

Ozone O 3 is the second allotropic modification of oxygen.
The triatomic ozone molecule has a corner structure midway between the two structures represented by the following formulas:

Ozone is a dark blue gas with a pungent odor. Due to its strong oxidative activity, it is poisonous. Ozone is one and a half times "heavier" than oxygen and somewhat more than oxygen, soluble in water.
Ozone is formed in the atmosphere from oxygen during lightning electrical discharges:

3O 2 \u003d 2O 3 ().

At ordinary temperatures, ozone slowly turns into oxygen, and when heated, this process proceeds with an explosion.
Ozone is contained in the so-called "ozone layer" of the earth's atmosphere, protecting all life on Earth from the harmful effects of solar radiation.
In some cities, ozone is used instead of chlorine to disinfect (decontaminate) drinking water.

Draw the structural formulas of the following substances: OF 2 , H 2 O, H 2 O 2 , H 3 PO 4 , (H 3 O) 2 SO 4 , BaO, BaO 2 , Ba(OH) 2 . Name these substances. Describe the valence states of the oxygen atoms in these compounds.
Determine the valency and oxidation state of each of the oxygen atoms.
2. Make the equations for the reactions of combustion in oxygen of lithium, magnesium, aluminum, silicon, red phosphorus and selenium (the atoms of selenium are oxidized to the oxidation state + IV, the atoms of the remaining elements to the highest oxidation state). What classes of oxides do the products of these reactions belong to?
3. How many liters of ozone can be obtained (under normal conditions) a) from 9 liters of oxygen, b) from 8 g of oxygen?

Water is the most abundant substance in the earth's crust. The mass of earth's water is estimated at 10 18 tons. Water is the basis of the hydrosphere of our planet, in addition, it is contained in the atmosphere, in the form of ice it forms the polar caps of the Earth and high-mountain glaciers, and is also part of various rocks. The mass fraction of water in the human body is about 70%.
Water is the only substance that has its own special names in all three states of aggregation.

The electronic structure of the water molecule (Fig. 10.4 A) we have studied in detail earlier (see § 7.10).
Due to the polarity of the O–H bonds and the angular shape, the water molecule is electric dipole.

To characterize the polarity of an electric dipole, a physical quantity called " electric moment of an electric dipole or simply " dipole moment".

In chemistry, the dipole moment is measured in debyes: 1 D = 3.34. 10–30 C. m

In a water molecule there are two polar covalent bonds, that is, two electric dipoles, each of which has its own dipole moment (and). The total dipole moment of a molecule is equal to the vector sum of these two moments (Fig. 10.5):

(H 2 O) = ,

Where q 1 and q 2 - partial charges (+) on hydrogen atoms, and and - interatomic distances O - H in the molecule. Because q 1 = q 2 = q, a , then

The experimentally determined dipole moments of the water molecule and some other molecules are given in the table.

Table 30Dipole moments of some polar molecules

Molecule		Molecule		Molecule

Given the dipole nature of the water molecule, it is often schematically depicted as follows:
Pure water is a colorless liquid without taste or smell. Some basic physical characteristics of water are given in the table.

Table 31Some physical characteristics of water

The large values ​​of the molar heats of melting and vaporization (an order of magnitude greater than those of hydrogen and oxygen) indicate that water molecules, both in solid and liquid substances, are quite strongly bonded to each other. These connections are called hydrogen bonds".

ELECTRIC DIPOLE, DIPOLE MOMENT, COMMUNICATION POLARITY, MOLECULE POLARITY.
How many valence electrons of an oxygen atom take part in the formation of bonds in a water molecule?
2. When overlapping which orbitals, bonds are formed between hydrogen and oxygen in a water molecule?
3. Make a diagram of the formation of bonds in a molecule of hydrogen peroxide H 2 O 2. What can you say about the spatial structure of this molecule?
4. Interatomic distances in HF, HCl and HBr molecules are equal, respectively, to 0.92; 1.28 and 1.41. Using the table of dipole moments, calculate and compare the partial charges on the hydrogen atoms in these molecules.
5. Interatomic distances S - H in a hydrogen sulfide molecule are equal to 1.34, and the angle between bonds is 92 °. Determine the values ​​of partial charges on sulfur and hydrogen atoms. What can you say about the hybridization of the valence orbitals of the sulfur atom?

10.4. hydrogen bond

As you already know, due to the significant difference in the electronegativity of hydrogen and oxygen (2.10 and 3.50), the hydrogen atom in the water molecule acquires a large positive partial charge ( q h = 0.33 e), and the oxygen atom has an even larger negative partial charge ( q h = -0.66 e). Recall also that the oxygen atom has two lone pairs of electrons per sp 3-hybrid AO. The hydrogen atom of one water molecule is attracted to the oxygen atom of another molecule, and, in addition, the half-empty 1s-AO of the hydrogen atom partially accepts a pair of electrons from the oxygen atom. As a result of these interactions between molecules, a special type of intermolecular bonds arises - a hydrogen bond.
In the case of water, hydrogen bond formation can be schematically represented as follows:

In the last structural formula, three dots (dashed stroke, not electrons!) Show a hydrogen bond.

Hydrogen bonding exists not only between water molecules. It is formed if two conditions are met:
1) there is a strongly polar H–E bond in the molecule (E is the symbol of an atom of a sufficiently electronegative element),
2) in the molecule there is an atom E with a large negative partial charge and an unshared pair of electrons.
As element E can be fluorine, oxygen and nitrogen. Hydrogen bonds are much weaker if E is chlorine or sulfur.
Examples of substances with a hydrogen bond between molecules: hydrogen fluoride, solid or liquid ammonia, ethyl alcohol and many others.

In liquid hydrogen fluoride, its molecules are linked by hydrogen bonds into rather long chains, while in liquid and solid ammonia, three-dimensional networks are formed.
The strength of the hydrogen bond is intermediate between chemical bond and other types of intermolecular bonds. The molar energy of the hydrogen bond usually lies in the range from 5 to 50 kJ/mol.
In solid water (that is, ice crystals), all hydrogen atoms are hydrogen bonded to oxygen atoms, with each oxygen atom forming two hydrogen bonds (using both lone pairs of electrons). Such a structure makes ice more "loose" compared to liquid water, where some of the hydrogen bonds are broken, and the molecules get the opportunity to "pack" somewhat more densely. This feature of the structure of ice explains why, unlike most other substances, water in the solid state has a lower density than in the liquid state. Water reaches its maximum density at 4 ° C - at this temperature, quite a lot of hydrogen bonds are broken, and thermal expansion does not yet have a very strong effect on density.
Hydrogen bonds are very important in our life. Imagine for a moment that hydrogen bonds have ceased to form. Here are some consequences:

• water at room temperature would become gaseous as its boiling point would drop to about -80°C;
• all reservoirs would begin to freeze from the bottom, since the density of ice would be greater than the density of liquid water;
• the DNA double helix would cease to exist, and much more.

The examples given are enough to understand that in this case, nature on our planet would be completely different.

HYDROGEN BOND, CONDITIONS OF ITS FORMATION.
The formula of ethyl alcohol is CH 3 -CH 2 -O-H. Between what atoms of different molecules of this substance are hydrogen bonds formed? Make structural formulas illustrating their formation.
2. Hydrogen bonds exist not only in individual substances, but also in solutions. Show with structural formulas how hydrogen bonds are formed in an aqueous solution of a) ammonia, b) hydrogen fluoride, c) ethanol (ethyl alcohol). \u003d 2H 2 O.
Both of these reactions proceed in water constantly and at the same rate, therefore, there is an equilibrium in water: 2H 2 O AN 3 O + OH.
This balance is called autoprotolysis equilibrium water.

The direct reaction of this reversible process is endothermic, therefore, when heated, autoprotolysis increases, while at room temperature, the equilibrium is shifted to the left, that is, the concentrations of H 3 O and OH ions are negligible. What are they equal to?
According to the law of mass action

But due to the fact that the number of reacted water molecules is insignificant compared to the total number of water molecules, we can assume that the water concentration during autoprotolysis practically does not change, and 2 = const Such a low concentration of oppositely charged ions in pure water explains why this liquid, although poorly, still conducts electric current.

AUTOPROTOLYSIS OF WATER, AUTOPROTOLYSIS CONSTANT (IONIC PRODUCT) OF WATER.
The ionic product of liquid ammonia (boiling point -33 ° C) is 2 10 -28. Write an equation for the autoprotolysis of ammonia. Determine the concentration of ammonium ions in pure liquid ammonia. The electrical conductivity of which of the substances is greater, water or liquid ammonia?

1. Obtaining hydrogen and its combustion (reducing properties).
2. Obtaining oxygen and combustion of substances in it (oxidizing properties).

Oxygen is one of the most abundant elements on earth. It makes up about half the weight of the earth's crust, the planet's outer shell. In combination with hydrogen, it forms water, covering more than two-thirds of the earth's surface.

We cannot see oxygen, nor can we taste or smell it. However, it makes up one fifth of the air and is vital. To live, we, like animals and plants, need to breathe.

Oxygen is an indispensable participant in chemical reactions that take place inside any microscopic cell of a living organism, as a result of which nutrients and the energy needed for life is released. That is why oxygen is so necessary for every living being (with the exception of a few types of microbes).

When burning, substances combine with oxygen, releasing energy in the form of heat and light.

Hydrogen

The most common element in the universe is hydrogen. It accounts for the bulk of most stars. On Earth, most of the hydrogen (chemical symbol H) is bound to oxygen (O) to form water (H20). Hydrogen is the simplest and most light chemical element, since each of its atom consists of only one proton and one electron.

At the beginning of the 20th century, airships and large aircraft were filled with hydrogen. However, hydrogen is very flammable. After several catastrophes caused by fires, hydrogen was no longer used in airships. Today, another light gas is used in aeronautics - non-flammable helium.

Hydrogen combines with carbon to form substances called hydrocarbons. These include products derived from natural gas and crude oil, such as gaseous propane and butane, or liquid gasoline. Hydrogen also combines with carbon and oxygen to form carbohydrates. The starch in potatoes and rice and the sugar in beets are carbohydrates.

The sun and other stars are mostly made up of hydrogen. In the center of the star, monstrous temperatures and pressures force hydrogen atoms to merge with each other and turn into another gas - helium. This releases a huge amount of energy in the form of heat and light.

• Designation - H (Hydrogen);
• Latin name - Hydrogenium;
• Period - I;
• Group - 1 (Ia);
• Atomic mass - 1.00794;
• Atomic number - 1;
• Radius of an atom = 53 pm;
• Covalent radius = 32 pm;
• The distribution of electrons - 1s 1;
• melting point = -259.14°C;
• boiling point = -252.87°C;
• Electronegativity (according to Pauling / according to Alpred and Rochov) \u003d 2.02 / -;
• Oxidation state: +1; 0; -1;
• Density (n.a.) \u003d 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. This is the simplest element in nature - a hydrogen atom has a nucleus and one electron, probably for this reason hydrogen is the most common element in the universe (more than half the mass of most stars).

About hydrogen, we can say that "the spool is small, but expensive." Despite its "simplicity", hydrogen gives 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 an enormous 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 vast majority (95%) of all known on Earth chemical substances 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, showing 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, takes on its only s-orbital one more electron, thus trying to complete its electron layer, showing an oxidation state of -1 (less often), forming more often an ionic bond (see Ionic bond), since the difference in the electronegativity of a hydrogen atom and a metal atom can be quite large.

H2

In the gaseous state, hydrogen is in the form of diatomic molecules, forming a non-polar 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 in platinum and palladium);
• difficult to liquefy (because of its low polarizability);
• has the highest thermal conductivity of all known gases;
• when heated, it reacts with many non-metals, showing 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, showing oxidizing properties: H 2 + Ca = CaH 2;

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

Fe 2 O 3 + 3H 2 \u003d 2Fe + 3H 2 O

Reactions of hydrogen with simple substances

Hydrogen accepts an electron, playing the 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 \u003d 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 \u003d 2H +1 Cl
• With fluorine: H 2 0 + F 2 \u003d 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 the role oxidizing agent, in reactions with alkaline And alkaline earth metals to form metal hydrides - salt-like ionic compounds containing hydride ions H - are unstable crystalline substances of white color.

Ca + H 2 \u003d CaH 2 -1 2Na + H 2 0 \u003d 2NaH -1

It is uncommon for hydrogen to exhibit an oxidation state of -1. Reacting with water, hydrides decompose, reducing water to hydrogen. The reaction of calcium hydride with water is as follows:

CaH 2 -1 + 2H 2 +1 0 \u003d 2H 2 0 + Ca (OH) 2

Reactions of hydrogen with complex substances

• at high temperature, hydrogen reduces many metal oxides: ZnO + H 2 \u003d Zn + H 2 O
• methyl alcohol is obtained as a result of the reaction of hydrogen with carbon monoxide (II): 2H 2 + CO → CH 3 OH
• in hydrogenation reactions, hydrogen reacts with many organic substances.

In more detail, the equations of chemical reactions of hydrogen and its compounds are considered on the page "Hydrogen and its compounds - equations of chemical reactions involving hydrogen".

Application 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, and hydrogen chloride;
• V Food Industry hydrogen is used in the production of solid fats through hydrogenation vegetable oils;
• for welding and cutting metals, a 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 balloons, balloons, airships;
• As a fuel, hydrogen is used mixed with CO.

Recently, scientists have paid 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 a 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 steam (t=500°C) on a Fe 2 O 3 catalyst: CO + H 2 O = CO 2 + H 2 ;
• thermal decomposition of methane: CH 4 \u003d C + 2H 2;
• gasification solid fuels(t=1000°C): C + H 2 O = CO + H 2 ;
• electrolysis of water (a very expensive method in which very pure hydrogen is obtained): 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 \u003d ZCl 2 + H 2; Zn + H 2 SO 4 \u003d ZnSO 4 + H 2;
• the interaction of water vapor with hot iron shavings: 4H 2 O + 3Fe \u003d Fe 3 O 4 + 4H 2.

Chemical properties of hydrogen

Under normal conditions, molecular Hydrogen is relatively inactive, combining directly with only the most active nonmetals (with fluorine, and in the light also with chlorine). However, when heated, it reacts with many elements.

Hydrogen reacts with simple and complex substances:

- Interaction of hydrogen with metals leads to the formation of complex substances - hydrides, in the chemical formulas of which the metal atom always comes first:

At high temperature, hydrogen reacts directly with some metals(alkaline, alkaline earth and others), forming white crystalline substances - metal hydrides (Li H, Na H, KH, CaH 2, etc.):

H 2 + 2Li = 2LiH

Metal hydrides are easily decomposed by water with the formation of the corresponding alkali and hydrogen:

Sa H 2 + 2H 2 O \u003d Ca (OH) 2 + 2H 2

- When hydrogen interacts with non-metals volatile hydrogen compounds are formed. IN chemical formula volatile hydrogen compound, the hydrogen atom can be either in the first or in the second place, depending on the location in the PSCE (see the plate in the slide):

1). With oxygen Hydrogen forms water:

Video "Combustion of hydrogen"

2H 2 + O 2 \u003d 2H 2 O + Q

At ordinary temperatures, the reaction proceeds extremely slowly, above 550 ° C - with an explosion (a mixture of 2 volumes of H 2 and 1 volume of O 2 is called explosive gas) .

Video "Explosion of explosive gas"

Video "Preparation and explosion of an explosive mixture"

2). With halogens Hydrogen forms hydrogen halides, for example:

H 2 + Cl 2 \u003d 2HCl

Hydrogen 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.

3). With nitrogen Hydrogen reacts with the formation of ammonia:

ZN 2 + N 2 \u003d 2NH 3

only on a catalyst and at elevated temperatures and pressures.

4). When heated, hydrogen reacts vigorously with sulfur:

H 2 + S \u003d H 2 S (hydrogen sulfide),

much more difficult with selenium and tellurium.

5). with pure carbon Hydrogen can react without a catalyst only at high temperatures:

2H 2 + C (amorphous) = CH 4 (methane)

- Hydrogen enters into a substitution reaction with metal oxides , while water is formed in the products and the metal is reduced. Hydrogen - exhibits the properties of a reducing agent:

Hydrogen is used for the recovery of many metals, since it takes away oxygen from their oxides:

Fe 3 O 4 + 4H 2 \u003d 3Fe + 4H 2 O, etc.

Application of hydrogen

Video "Use of hydrogen"

Currently, hydrogen is produced in huge quantities. A very large part of it is used in the synthesis of ammonia, the hydrogenation of fats and the hydrogenation of coal, oils and hydrocarbons. In addition, hydrogen is used for the synthesis of hydrochloric acid, methyl alcohol, hydrocyanic acid, in welding and forging metals, as well as in the manufacture of incandescent lamps and precious stones. Hydrogen goes on sale in cylinders under pressure over 150 atm. They are painted dark green and are supplied with a red inscription "Hydrogen".

Hydrogen is used to convert liquid fats into solid fats (hydrogenation), to produce liquid fuels by hydrogenating coal and fuel oil. In metallurgy, hydrogen is used as a reducing agent for oxides or chlorides to produce metals and non-metals (germanium, silicon, gallium, zirconium, hafnium, molybdenum, tungsten, etc.).

The practical application of hydrogen is diverse: it is usually filled with balloons, in the chemical industry it serves as a raw material for the production of many very important products (ammonia, etc.), in the food industry - for the production of solid fats from vegetable oils, etc. High temperature (up to 2600 °C), obtained by burning hydrogen in oxygen, is used to melt refractory metals, quartz, etc. Liquid hydrogen is one of the most efficient jet fuels. The annual world consumption of hydrogen exceeds 1 million tons.

SIMULATORS

No. 2. Hydrogen

TASKS FOR REINFORCEMENT

Task number 1
Make up the equations for the reactions of the interaction of hydrogen with the following substances: F 2 , Ca, Al 2 O 3 , mercury oxide (II), tungsten oxide (VI). Name the reaction products, indicate the types of reactions.

Task number 2
Carry out the transformations according to the scheme:
H 2 O -> H 2 -> H 2 S -> SO 2

Task number 3.
Calculate the mass of water that can be obtained by burning 8 g of hydrogen?

Oxygen is the most abundant element on earth. Together with nitrogen and a small amount of other gases, free oxygen forms the Earth's atmosphere. Its content in air is 20.95% by volume or 23.15% by mass. In the earth's crust, 58% of the atoms are atoms of bound oxygen (47% by mass). Oxygen is part of water (the reserves of bound oxygen in the hydrosphere are extremely large), rocks, many minerals and salts, and is found in fats, proteins and carbohydrates that make up living organisms. Almost all of the free oxygen on Earth is created and stored as a result of the process of photosynthesis.

physical properties.

Oxygen is a colorless, tasteless and odorless gas, slightly heavier than air. It is slightly soluble in water (31 ml of oxygen dissolves in 1 liter of water at 20 degrees), but it is still better than other atmospheric gases, so water is enriched with oxygen. The density of oxygen under normal conditions is 1.429 g/l. At a temperature of -183 0 C and a pressure of 101.325 kPa, oxygen passes into a liquid state. Liquid oxygen has a bluish color, is drawn into the magnetic field, and at -218.7 ° C, forms blue crystals.

Natural oxygen has three isotopes O 16, O 17, O 18.

Allotropy- ability chemical element exist in the form of two or more simple substances that differ only in the number of atoms in the molecule, or in structure.

Ozone O 3 - exists in upper layers atmosphere at an altitude of 20-25 km from the Earth's surface and forms the so-called "ozone layer", which protects the Earth from destructive ultraviolet radiation sun; pale purple, poisonous gas in large quantities with a specific, pungent, but pleasant smell. The melting point is -192.7 0 C, the boiling point is -111.9 0 C. Let's dissolve in water better than oxygen.

Ozone is a strong oxidizing agent. Its oxidizing activity is based on the ability of the molecule to decompose with the release of atomic oxygen:

It oxidizes many simple and complex substances. It forms ozonides with some metals, for example, potassium ozonide:

K + O 3 \u003d KO 3

Ozone is obtained from special devices- ozonators. In them, under the action of an electric discharge, molecular oxygen is converted into ozone:

A similar reaction occurs under the action of lightning discharges.

The use of ozone is due to its strong oxidizing properties: it is used for bleaching fabrics, disinfecting drinking water, in medicine as a disinfectant.

Inhalation of ozone in large quantities is harmful: it irritates the mucous membranes of the eyes and respiratory organs.

Chemical properties.

IN chemical reactions with atoms of other elements (except fluorine), oxygen exhibits exclusively oxidizing properties

The most important chemical property- the ability to form oxides with almost all elements. At the same time, oxygen reacts directly with most substances, especially when heated.

As a result of these reactions, as a rule, oxides are formed, less often peroxides:

2Ca + O 2 \u003d 2CaO

2Ва + О 2 = 2ВаО

2Na + O 2 \u003d Na 2 O 2

Oxygen does not interact directly with halogens, gold, platinum, their oxides are obtained indirectly. When heated, sulfur, carbon, phosphorus burn in oxygen.

The interaction of oxygen with nitrogen begins only at a temperature of 1200 0 C or in an electric discharge:

N 2 + O 2 \u003d 2NO

Oxygen combines with hydrogen to form water:

2H 2 + O 2 \u003d 2H 2 O

During this reaction, a significant amount of heat is released.

A mixture of two volumes of hydrogen with one oxygen explodes when ignited; it is called explosive gas.

Many metals in contact with atmospheric oxygen undergo destruction - corrosion. Some metals under normal conditions are oxidized only from the surface (for example, aluminum, chromium). The resulting oxide film prevents further interaction.

4Al + 3O 2 \u003d 2Al 2 O 3

Complex substances under certain conditions also interact with oxygen. In this case, oxides are formed, and in some cases, oxides and simple substances.

CH 4 + 2O 2 \u003d CO 2 + 2H 2 O

H 2 S + O 2 \u003d 2SO 2 + 2H 2 O

4NH 3 + ZO 2 \u003d 2N 2 + 6H 2 O

4CH 3 NH 2 + 9O 2 = 4CO 2 + 2N 2 + 10H 2 O

When interacting with complex substances, oxygen acts as an oxidizing agent. Its important property is based on the oxidative activity of oxygen - the ability to maintain combustion substances.

With hydrogen, oxygen also forms a compound - hydrogen peroxide H 2 O 2 - a colorless transparent liquid with a burning astringent taste, highly soluble in water. Chemically, hydrogen peroxide is a very interesting compound. Its low stability is characteristic: when standing, it slowly decomposes into water and oxygen:

H 2 O 2 \u003d H 2 O + O 2

Light, heat, the presence of alkalis, contact with oxidizing or reducing agents accelerate the decomposition process. The degree of oxidation of oxygen in hydrogen peroxide = - 1, i.e. has an intermediate value between the oxidation state of oxygen in water (-2) and in molecular oxygen (0), so hydrogen peroxide exhibits redox duality. The oxidizing properties of hydrogen peroxide are much more pronounced than the reducing ones, and they appear in acidic, alkaline and neutral media.

H 2 O 2 + 2KI + H 2 SO 4 \u003d K 2 SO 4 + I 2 + 2H 2 O