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 the destructive ultraviolet radiation of the 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 in special devices - ozonizers. 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 is 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.

Oxygen also forms a compound with hydrogen - 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

Hydrogen H is the most common element in the Universe (about 75% by mass), on Earth it is the ninth most common element. The most important natural hydrogen compound is water.
Hydrogen ranks first in the periodic table (Z = 1). It has the simplest structure of an atom: the nucleus of an atom is 1 proton, surrounded by an electron cloud consisting of 1 electron.
Under some conditions, hydrogen exhibits metallic properties (donates an electron), in others - non-metallic (accepts an electron).
Hydrogen isotopes are found in nature: 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).

The simple substance hydrogen

The hydrogen molecule consists of two atoms linked by a non-polar covalent bond.
physical properties. Hydrogen is a colorless, non-toxic, odorless and tasteless gas. The hydrogen molecule is not polar. Therefore, the forces of intermolecular interaction in gaseous hydrogen are small. This manifests itself in low temperatures boiling (-252.6 0С) and melting (-259.2 0С).
Hydrogen is lighter than air, D (in 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.

Getting hydrogen

In the laboratory:

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

2. Interaction of alkaline and sh-z metals with water:
Ca + 2H 2 O → Ca (OH) 2 + H 2

3. Hydrolysis of hydrides: metal hydrides are easily decomposed by water with the formation of the corresponding alkali and hydrogen:
NaH + H 2 O → NaOH + H 2
CaH 2 + 2H 2 O \u003d Ca (OH) 2 + 2H 2

4. The action 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. Water electrolysis. 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. At the cathode, 2 volumes of hydrogen are formed, at the anode - 1 volume of oxygen.
2H 2 O → 2H 2 + O 2

Industrial production of hydrogen

1. Conversion of methane 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, in this way 50% of industrial hydrogen is obtained.

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

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

Chemical properties of hydrogen

• In compounds, hydrogen is always monovalent. It has an oxidation state of +1, but in metal hydrides it is -1.
• The hydrogen molecule consists of two atoms. The emergence of a bond between them is explained by the formation of a generalized pair of electrons H: H or H 2
• Due to this generalization of electrons, the H 2 molecule is more energetically stable than its individual atoms. To break a molecule into atoms in 1 mole of hydrogen, it is necessary to expend an energy of 436 kJ: H 2 \u003d 2H, ∆H ° \u003d 436 kJ / mol
• This explains the relatively low activity of molecular hydrogen at ordinary temperature.
• With many non-metals, hydrogen forms gaseous compounds such as RN 4, RN 3, RN 2, RN.

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 ordinary temperatures, the reaction proceeds 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.

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 the 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, the hydride Na + H - is built like chloride Na + Cl -

With complex substances:

7) With metal oxides (used to restore 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) has an important practical value, maybe, depending on the temperature, pressure and catalyst, various organic compounds are formed, for example, HCHO, CH 3 OH and others.

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

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 chemical reactions going inside any microscopic cell of a living organism, as a result of which they split 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 lightest chemical element, since each of its atoms 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.

The purpose of the lesson. In this lesson, you will learn about perhaps the most important chemical elements for life on earth - hydrogen and oxygen, learn about their chemical properties, as well as the physical properties of the simple substances they form, learn more about the role of oxygen and hydrogen in nature and life person.

Hydrogen is the most abundant element in the universe. Oxygen is the most abundant element on earth. Together they form water, a substance that makes up more than half of the mass of the human body. Oxygen is the gas we need to breathe, and without water we could not live even a few days, so without a doubt, oxygen and hydrogen can be considered the most important chemical elements necessary for life.

The structure of hydrogen and oxygen atoms

Thus, hydrogen exhibits non-metallic properties. Hydrogen occurs naturally in three isotopes, protium, deuterium and tritium, hydrogen isotopes are very different from each other in physical properties, so they are even assigned individual symbols.

If you do not remember or do not know what isotopes are, work with the materials of the electronic educational resource "Isotopes as varieties of atoms of one chemical element." In it, you will learn how the isotopes of one element differ from each other, what the presence of several isotopes in one element leads to, and also get acquainted with the isotopes of several elements.

Thus, the possible oxidation states of oxygen are limited to values ​​from –2 to +2. If oxygen accepts two electrons (becoming an anion) or forms two covalent bonds with less electronegative elements, it goes into the -2 oxidation state. If oxygen forms one bond with another oxygen atom, and the second with an atom of a less electronegative element, it goes into the -1 oxidation state. Forming two covalent bonds with fluorine (the only element with more high value electronegativity), oxygen goes into the +2 oxidation state. Forming one bond with another oxygen atom, and the second with a fluorine atom - +1. Finally, if oxygen forms one bond with a less electronegative atom and a second bond with fluorine, it will be in oxidation state 0.

Physical properties of hydrogen and oxygen, allotropy of oxygen

Hydrogen- colorless gas without taste and smell. Very light (14.5 times lighter than air). The temperature of hydrogen liquefaction - -252.8 ° C - is almost the lowest among all gases (second only to helium). Liquid and solid hydrogen are very light, colorless substances.

Oxygen It is a colorless, odorless, tasteless gas, slightly heavier than air. At -182.9 °C it turns into a heavy blue liquid, at -218 °C it solidifies with the formation of crystals of blue color. Oxygen molecules are paramagnetic, which means that oxygen is attracted to a magnet. Oxygen is poorly soluble in water.

Unlike hydrogen, which forms molecules of only one type, oxygen exhibits allotropy and forms molecules of two types, that is, the element oxygen forms two simple substances: oxygen and ozone.

Chemical properties and obtaining simple substances

Hydrogen.

The bond in the hydrogen molecule is single, but it is one of the strongest single bonds in nature, and it takes a lot of energy to break it, for this reason hydrogen is very inactive at room temperature, however, when the temperature rises (or in the presence of a catalyst), hydrogen easily interacts with many simple and complex substances.

Hydrogen is a typical non-metal from a chemical point of view. That is, it is able to interact with active metals to form hydrides, in which it exhibits an oxidation state of -1. With some metals (lithium, calcium), the interaction proceeds even at room temperature, but rather slowly, therefore, heating is used in the synthesis of hydrides:

,

.

The formation of hydrides by direct interaction of simple substances is possible only for active metals. Already aluminum does not interact directly with hydrogen, its hydride is obtained by exchange reactions.

Hydrogen also reacts with non-metals only when heated. Exceptions are the halogens chlorine and bromine, the reaction with which can be induced by light:

.

The reaction with fluorine also does not require heating; it proceeds with an explosion even with strong cooling and in absolute darkness.

The reaction with oxygen proceeds according to a branched chain mechanism, therefore the reaction rate increases rapidly, and in a mixture of oxygen and hydrogen in a ratio of 1: 2, the reaction proceeds with an explosion (such a mixture is called "explosive gas"):

.

The reaction with sulfur proceeds much more quietly, with little or no heat release:

.

Reactions with nitrogen and iodine proceed reversibly:

,

.

This circumstance greatly complicates the production of ammonia in industry: the process requires the use of elevated pressure to mix the equilibrium in the direction of ammonia formation. Hydrogen iodine is not obtained by direct synthesis, since there are several much more convenient ways its synthesis.

Hydrogen does not directly react with low-active non-metals (), although its compounds with them are known.

In reactions with complex substances, hydrogen in most cases acts as a reducing agent. In solutions, hydrogen can reduce low-active metals (located after hydrogen in the series of voltages) from their salts:

When heated, hydrogen can reduce many metals from their oxides. Moreover, the more active the metal, the more difficult it is to restore it and the higher the temperature required for this:

.

Metals more active than zinc are practically impossible to reduce with hydrogen.

Hydrogen is produced in the laboratory by reacting metals with strong acids. The most commonly used zinc and hydrochloric acid:

Less commonly used electrolysis of water in the presence of strong electrolytes:

In industry, hydrogen is produced as a by-product in the production of caustic soda by electrolysis of a sodium chloride solution:

In addition, hydrogen is obtained during oil refining.

The production of hydrogen by photolysis of water is one of the most promising methods in the future, but at the moment industrial application this method is difficult.

Work with materials of electronic educational resources Laboratory work"Obtaining and properties of hydrogen" and Laboratory work "reducing properties of hydrogen". Learn the principle of operation of the Kipp apparatus and the Kiryushkin apparatus. Think about in which cases it is more convenient to use the Kipp apparatus, and in which - Kiryushkin. What properties does hydrogen exhibit in reactions?

Oxygen.

The bond in the oxygen molecule is double and very strong. Therefore, oxygen is rather inactive at room temperature. When heated, however, it begins to exhibit strong oxidizing properties.

Oxygen reacts without heating with active metals (alkali, alkaline earth and some lanthanides):

When heated, oxygen reacts with most metals to form oxides:

,

,

.

Silver and less active metals are not oxidized by oxygen.

Oxygen also reacts with most non-metals to form oxides:

,

,

.

Interaction with nitrogen occurs only at very high temperatures, around 2000 °C.

Oxygen does not react with chlorine, bromine and iodine, although many of their oxides can be obtained indirectly.

The interaction of oxygen with fluorine can be carried out by passing an electric discharge through a mixture of gases:

.

Oxygen(II) fluoride is an unstable compound, easily decomposed and a very strong oxidizing agent.

In solutions, oxygen is a strong, albeit slow, oxidizing agent. As a rule, oxygen promotes the transition of metals to higher oxidation states:

The presence of oxygen often makes it possible to dissolve in acids metals located immediately after hydrogen in the voltage series:

When heated, oxygen can oxidize lower metal oxides:

.

Oxygen is not obtained chemically in industry, it is obtained from the air by distillation.

The laboratory uses decomposition reactions of oxygen-rich compounds - nitrates, chlorates, permanganates when heated:

You can also get oxygen by catalytic decomposition of hydrogen peroxide:

In addition, the above water electrolysis reaction can be used to produce oxygen.

Work with the materials of the electronic educational resource Laboratory work "Production of oxygen and its properties."

What is the name of the oxygen collection method used in laboratory work? What other ways of collecting gases are there and which ones are suitable for collecting oxygen?

Task 1. Watch the video clip "Decomposition of potassium permanganate when heated."

Answer the questions:

1. 1. Which of the solid products of the reaction is soluble in water?
   2. What color is potassium permanganate solution?
   3. What is the color of potassium manganate solution?

Write the equations for the ongoing reactions. Equalize them using the electronic balance method.

Discuss the task with the teacher on or in the video room.

Ozone.

The ozone molecule is triatomic and the bonds in it are less strong than in the oxygen molecule, which leads to a greater chemical activity of ozone: ozone easily oxidizes many substances in solutions or in dry form without heating:

Ozone is able to easily oxidize nitric oxide (IV) to nitric oxide (V), and sulfur oxide (IV) to sulfur oxide (VI) without a catalyst:

Ozone gradually decomposes to form oxygen:

Used to produce ozone special devices- ozonizers, in which a glow discharge is passed through oxygen.

In the laboratory, to obtain small amounts of ozone, decomposition reactions of peroxo compounds and some higher oxides are sometimes used when heated:

Work with the materials of the electronic educational resource Laboratory work "Obtaining ozone and studying its properties."

Explain why the indigo solution becomes colorless. Write the equations for the reactions that occur when solutions of lead nitrate and sodium sulfide are mixed and when ozonized air is passed through the resulting suspension. Write ionic equations for the ion exchange reaction. For the redox reaction, make an electronic balance.

Discuss the task with the teacher on or in the video room.

Chemical properties of water

For a better acquaintance with physical properties water and its significance, work with the materials of electronic educational resources "Anomalous properties of water" and "Water is the most important liquid on Earth."

Water is of great importance for any living organisms - in fact, many living organisms are made up of more than half water. Water is one of the most versatile solvents (at high temperatures and pressures, its capabilities as a solvent increase significantly). From a chemical point of view, water is hydrogen oxide, while in aqueous solution it dissociates (albeit to a very small extent) into hydrogen cations and hydroxide anions:

.

Water interacts with many metals. With active (alkaline, alkaline earth and some lanthanides) water reacts without heating:

With less active interaction occurs when heated.

General and inorganic chemistry

Lecture 6. Hydrogen and oxygen. Water. Hydrogen peroxide.

Hydrogen

The hydrogen atom is the simplest object of chemistry. Strictly speaking, its ion - the proton - is even simpler. First described in 1766 by Cavendish. Name from Greek. "hydro genes" - generating water.

The radius of a hydrogen atom is approximately 0.5 * 10-10 m, and its ion (proton) is 1.2 * 10-15 m. Or from 50 pm to 1.2 * 10-3 pm or from 50 meters (SCA diagonal ) up to 1 mm.

The next 1s element, lithium, only changes from 155 pm to 68 pm for Li+. Such a difference in the size of an atom and its cation (5 orders of magnitude) is unique.

Due to the small size of the proton, the exchange hydrogen bond, primarily between oxygen, nitrogen and fluorine atoms. The strength of hydrogen bonds is 10–40 kJ/mol, which is much less than the breaking energy of most ordinary bonds (100–150 kJ/mol in organic molecules), but more than the average kinetic energy of thermal motion at 370 C (4 kJ/mol). As a result, in a living organism, hydrogen bonds are reversibly broken, ensuring the flow of vital processes.

Hydrogen melts at 14 K, boils at 20.3 K (pressure 1 atm), the density of liquid hydrogen is only 71 g/l (14 times lighter than water).

In the rarefied interstellar medium, excited hydrogen atoms were found with transitions up to n 733 → 732 with a wavelength of 18 m, which corresponds to a Bohr radius (r = n2 * 0.5 * 10-10 m) of the order of 0.1 mm (!).

The most common element in space (88.6% of atoms, 11.3% of atoms are helium, and only 0.1% are atoms of all other elements).

4 H → 4 He + 26.7 MeV 1 eV = 96.48 kJ/mol

Since protons have spin 1/2, there are three types of hydrogen molecules:

orthohydrogen o-H2 with parallel nuclear spins, parahydrogen n-H2 with antiparallel spins and normal n-H2 - a mixture of 75% ortho-hydrogen and 25% para-hydrogen. During the transformation of o-H2 → p-H2, 1418 J/mol is released.

Properties of ortho- and parahydrogen

Since the atomic mass of hydrogen is the minimum possible, its isotopes - deuterium D (2 H) and tritium T (3 H) differ significantly from protium 1 H in physical and chemical properties. For example, replacing one of the hydrogens in organic compound on deuterium is noticeably reflected in its vibrational (infrared) spectrum, which makes it possible to establish the structure of complex molecules. Similar substitutions (“labeled atom method”) are also used to establish the mechanisms of complex

chemical and biochemical processes. The method of labeled atoms is especially sensitive when radioactive tritium is used instead of protium (β-decay, half-life 12.5 years).

Properties of protium and deuterium

					Density, g/l (20 K)
Main method hydrogen production in industry – methane conversion
or coal hydration at 800-11000 C (catalyst):
CH4 + H2 O = CO + 3 H2				above 10000 C
"Water gas": C + H2 O = CO + H2
Then CO conversion: CO + H2 O = CO2 + H2						4000 C, cobalt oxides

Total: C + 2 H2 O = CO2 + 2 H2

Other sources of hydrogen.

Coke oven gas: about 55% hydrogen, 25% methane, up to 2% heavy hydrocarbons, 4-6% CO, 2% CO2, 10-12% nitrogen.

Hydrogen as a combustion product:

Si + Ca(OH)2 + 2 NaOH = Na2 SiO3 + CaO + 2 H2

Up to 370 liters of hydrogen are released per 1 kg of pyrotechnic mixture.

Hydrogen in the form a simple substance used for the production of ammonia and hydrogenation (hardening) of vegetable fats, for the reduction of some metal oxides (molybdenum, tungsten), for the production of hydrides (LiH, CaH2,

LiAlH4).

The enthalpy of the reaction: H. + H. = H2 is -436 kJ / mol, so atomic hydrogen is used to produce a high-temperature reducing “flame” (“Langmuir burner”). A jet of hydrogen in an electric arc is atomized at 35,000 C by 30%, then, with the recombination of atoms, it is possible to reach 50,000 C.

Liquefied hydrogen is used as fuel in rockets (see oxygen). Promising environmentally friendly fuel for land transport; experiments are underway on the use of hydrogen metal hydride batteries. For example, the LaNi5 alloy can absorb 1.5-2 times more hydrogen than is contained in the same volume (as the volume of the alloy) of liquid hydrogen.

Oxygen

According to now generally accepted data, oxygen was discovered in 1774 by J. Priestley and independently by K. Scheele. History of the discovery of oxygen good example the influence of paradigms on the development of science (see Appendix 1).

Apparently, in fact, oxygen was discovered much earlier than the official date. In 1620, anyone could ride along the Thames (in the Thames) in a submarine designed by Cornelius van Drebbel. The boat moved under water thanks to the efforts of a dozen rowers. According to numerous eyewitnesses, the inventor of the submarine successfully solved the problem of breathing by “refreshing” the air in it. by chemical means. Robert Boyle wrote in 1661: “... Except mechanical design boats, the inventor had chemical solution(liquor) which he

considered the main secret of scuba diving. And when from time to time he became convinced that the breathable part of the air had already been used up and made it difficult for people in the boat to breathe, he could, by opening a vessel filled with this solution, quickly replenish the air with such a content of vital parts that would make it again suitable for breath for a sufficiently long time.

A healthy person in a calm state per day pumps about 7200 liters of air through his lungs, taking 720 liters of oxygen irrevocably. In a closed room with a volume of 6 m3, a person can survive without ventilation for up to 12 hours, and with physical work 3-4 hours. The main cause of difficulty breathing is not a lack of oxygen, but accumulation of carbon dioxide from 0.3 to 2.5%.

For a long time The main method for obtaining oxygen was the "barium" cycle (obtaining oxygen by the Brin method):

BaSO4 -t-→ BaO + SO3;

5000C ->

BaO + 0.5 O2 ====== BaO2<- 7000 C

Drebbel's secret solution could be a solution of hydrogen peroxide: BaO2 + H2 SO4 = BaSO4 ↓ + H2 O2

Obtaining oxygen during combustion of the pyromixture: NaClO3 = NaCl + 1.5 O2 + 50.5 kJ

In a mixture of up to 80% NaClO3, up to 10% iron powder, 4% barium peroxide and glass wool.

The oxygen molecule is paramagnetic (practically a biradical), therefore its activity is high. Organic substances are oxidized in air through the stage of peroxide formation.

Oxygen melts at 54.8 K and boils at 90.2 K.

The allotropic modification of the element oxygen is the substance ozone O3. The biological ozone protection of the Earth is extremely important. At an altitude of 20-25 km, an equilibrium is established:

UV<280 нм		UV 280-320nm
O2 ----> 2 O*	O* + O2 + M --> O3	O3-------	> O2 + O
	(M - N2 , Ar)

In 1974, it was discovered that atomic chlorine, which is formed from freons at an altitude of more than 25 km, catalyzes the decay of ozone, as if replacing the "ozone" ultraviolet. This UV is capable of causing skin cancer (up to 600,000 cases per year in the US). The ban on freons in aerosol cans has been in effect in the United States since 1978.

Since 1990, the list of prohibited substances (in 92 countries) has included CH3 CCl3, CCl4, chlorobromohydrocarbons - their production is curtailed by 2000.

Combustion of hydrogen in oxygen

The reaction is very complex (scheme in lecture 3), so a long study was required before the start of practical application.

July 21, 1969 the first earthling - N. Armstrong walked on the moon. The Saturn-5 launch vehicle (designed by Wernher von Braun) consists of three stages. In the first, kerosene and oxygen, in the second and third - liquid hydrogen and oxygen. Total 468 tons of liquid O2 and H2. 13 successful launches were made.

Since April 1981, the Space Shuttle has been operating in the USA: 713 tons of liquid O2 and H2, as well as two solid-propellant boosters of 590 tons each (total mass solid fuel 987 tons). The first 40 km ascent to the TTU, from 40 to 113 km engines run on hydrogen and oxygen.

On May 15, 1987, the first launch of Energia, on November 15, 1988, the first and only flight of Buran. The launch weight is 2400 tons, the mass of fuel (kerosene in

side compartments, liquid O2 and H2) 2000 tons. Engine power 125000 MW, payload 105 tons.

The combustion was not always controlled and successful.

In 1936, the world's largest hydrogen airship LZ-129 "Hindenburg" was built. The volume is 200,000 m3, the length is about 250 m, the diameter is 41.2 m. The speed is 135 km / h thanks to 4 engines of 1100 hp each, the payload is 88 tons. The airship made 37 flights across the Atlantic and transported more than 3 thousand passengers.

On May 6, 1937, while mooring in the USA, the airship exploded and burned down. One of possible causes- sabotage.

On January 28, 1986, at the 74th second of the flight, the Challenger exploded with seven cosmonauts - the 25th flight of the Shuttle system. The reason is a defect in the solid propellant booster.

Demonstration:

explosive gas explosion (a mixture of hydrogen and oxygen)

fuel cells

Technically important option this combustion reaction - the division of the process into two:

hydrogen electrooxidation (anode): 2 H2 + 4 OH– - 4 e– = 4 H2 O

oxygen electroreduction (cathode): O2 + 2 H2 O + 4 e– = 4 OH–

The system in which such “burning” is carried out is fuel cell. The efficiency is much higher than that of thermal power plants, since there is no

special stage of heat generation. Maximum efficiency = ∆G/∆H; for the combustion of hydrogen, 94% is obtained.

The effect has been known since 1839, but the first practically working fuel cells have been implemented

at the end of the 20th century in space (“Gemini”, “Apollo”, “Shuttle” - USA, “Buran” - USSR).

Fuel Cell Perspectives [17]

A representative of Ballard Power Systems, speaking at a scientific conference in Washington, emphasized that a fuel cell engine will become commercially viable when it meets four main criteria: lower cost of generated energy, increased durability, reduced installation size and the ability to start quickly in cold weather. . The cost of one kilowatt of energy generated by a fuel cell plant should be reduced to $30. For comparison, in 2004 the same figure was $103, and in 2005 it is expected to be $80. To achieve this price, it is necessary to produce at least 500 thousand engines per year. European scientists are more cautious in their forecasts and believe that the commercial use of fuel hydrogen elements in the automotive industry will begin no earlier than 2020.