Why does the water not burn, although it consists of flammable substances (hydrogen and oxygen). Chemistry organics Hydrogen oxygen equation
§3. The reaction equation and how to compose it
Interaction hydrogen with oxygen as it was established by Sir Henry Cavendish, leads to the formation of water. Let's use this simple example to learn how to compose chemical reaction equations.
What comes out of hydrogen and oxygen, we already know:
H 2 + O 2 → H 2 O
Now let's take into account that the atoms of chemical elements in chemical reactions do not disappear and do not appear out of nothing, do not turn into each other, but connect in new combinations forming new molecules. This means that in the equation of the chemical reaction of atoms of each type there must be the same number before reactions ( left from the equal sign) and after the end of the reaction ( on right from the equal sign), like this:
2H 2 + O 2 = 2H 2 O
That's what it is reaction equation - conditional notation of the ongoing chemical reaction using formulas of substances and coefficients.
This means that in the given reaction two praying hydrogen should react with one pray oxygen, and the result will be two praying water.
Interaction hydrogen with oxygen is not an easy process at all. It leads to a change in the oxidation states of these elements. To select the coefficients in such equations, usually use the method " electronic balance".
When water is formed from hydrogen and oxygen, this means that hydrogen changed its oxidation state from 0 before + I, but oxygen- from 0 before −II... In this case, several (n) electrons:
Electron donating hydrogen serves here reducing agent, and oxygen accepting electrons - oxidizing agent.
Oxidizing and reducing agents
Let us now see how the processes of giving and receiving electrons look separately. Hydrogen, having met with the "robber" -oxygen, loses all its property - two electrons, and its oxidation state becomes equal + I:
H 2 0 - 2 e- = 2H + I
Happened oxidation half-reaction equation hydrogen.
And the bandit- oxygen About 2 having taken away the last electrons from the unfortunate hydrogen, he is very pleased with his new oxidation state -II:
O 2 + 4 e- = 2O −II
This is recovery half-reaction equation oxygen.
It remains to add that both the "bandit" and his "victim" have lost their chemical identity from simple substances - gases with diatomic molecules H 2 and About 2 turned into constituents of a new chemical - water H 2 O.
Further, we will argue as follows: how many electrons the reductant gave to the bandit-oxidizer, he received so much. The number of electrons donated by the reducing agent must be equal to the number of electrons donated by the oxidizing agent.
So it is necessary equalize the number of electrons in the first and second half-reactions. In chemistry, the following conditional form of writing the equations of half-reactions is adopted:
2 H 2 0 - 2 e- = 2H + I |
|
1 O 2 0 + 4 e- = 2O −II |
Here, the numbers 2 and 1 to the left of the curly brace are factors that will help ensure that the number of electrons given and received is equal. Let us take into account that in the equations of half-reactions 2 electrons are given, and 4 are accepted. To equalize the number of electrons received and given away, the smallest common multiple and additional factors are found. In our case, the least common multiple is 4. Additional factors will be 2 for hydrogen (4: 2 = 2), and for oxygen - 1 (4: 4 = 1)
The resulting factors will serve as the coefficients of the future reaction equation:
2H 2 0 + O 2 0 = 2H 2 + I O −II
Hydrogen oxidizes not only when meeting with oxygen... About the same effect on hydrogen and fluorine F 2, halogen and famous "robber", and seemingly harmless nitrogen N 2:
H 2 0 + F 2 0 = 2H + I F −I |
3H 2 0 + N 2 0 = 2N −III H 3 + I |
Thus it turns out hydrogen fluoride HF or ammonia NH 3.
In both compounds, the oxidation state hydrogen becomes equal + I, because partners in a molecule he gets "greedy" for someone else's electronic good, with high electronegativity - fluorine F and nitrogen N... Have nitrogen the value of electronegativity is considered equal to three conventional units, and in fluorine in general, the highest electronegativity among all chemical elements is four units. So it is not surprising for them to leave the poor thing, a hydrogen atom, without any electronic environment.
But hydrogen maybe restore- to accept electrons. This happens if alkali metals or calcium, which have less electronegativity than hydrogen, will participate in the reaction with it.
In the periodic table, hydrogen is located in two groups of elements that are absolutely opposite in their properties. This feature makes it completely unique. Hydrogen is not only an element or substance, but also a constituent part of many complex compounds, an organogenic and biogenic element. Therefore, we will consider its properties and characteristics in more detail.
The release of combustible gas during the interaction of metals and acids was observed as early as the 16th century, that is, during the formation of chemistry as a science. The famous English scientist Henry Cavendish studied the substance since 1766 and gave it the name "combustible air". When burned, this gas produced water. Unfortunately, the scientist's adherence to the theory of phlogiston (hypothetical "superfine matter") prevented him from coming to the correct conclusions.
The French chemist and naturalist A. Lavoisier together with the engineer J. Meunier and with the help of special gas meters in 1783 carried out the synthesis of water, and then its analysis by means of decomposition of water vapor with red-hot iron. Thus, scientists were able to come to the correct conclusions. They found that "combustible air" is not only a part of water, but can also be obtained from it.
In 1787, Lavoisier put forward the assumption that the gas under study is a simple substance and, accordingly, belongs to the number of primary chemical elements. He named it hydrogene (from the Greek words hydor - water + gennao - I give birth), that is, "giving birth to water."
The Russian name "hydrogen" was proposed in 1824 by chemist M. Soloviev. The determination of the composition of the water marked the end of the "phlogiston theory". At the turn of the 18th and 19th centuries, it was found that the hydrogen atom is very light (compared to the atoms of other elements) and its mass was taken as the main unit for comparing atomic masses, having received a value equal to 1.
Physical properties
Hydrogen is the lightest of all substances known to science (it is 14.4 times lighter than air), its density is 0.0899 g / l (1 atm, 0 ° C). This material melts (solidifies) and boils (liquefies), respectively, at -259.1 ° C and -252.8 ° C (only helium has lower boiling and melting points).
The critical temperature of hydrogen is extremely low (-240 ° C). For this reason, its liquefaction is a rather complicated and costly process. The critical pressure of the substance is 12.8 kgf / cm², and the critical density is 0.0312 g / cm³. Among all gases, hydrogen has the highest thermal conductivity: at 1 atm and 0 ° C, it is equal to 0.174 W / (mxK).
The specific heat capacity of a substance under the same conditions is 14.208 kJ / (kgxK) or 3.394 cal / (gx ° C). This element is slightly soluble in water (about 0.0182 ml / g at 1 atm and 20 ° C), but well - in most metals (Ni, Pt, Pa and others), especially in palladium (about 850 volumes per volume of Pd ).
The latter property is associated with its ability to diffuse, while diffusion through a carbon alloy (for example, steel) can be accompanied by the destruction of the alloy due to the interaction of hydrogen with carbon (this process is called decarbonization). In the liquid state, the substance is very light (density - 0.0708 g / cm³ at t ° = -253 ° C) and fluid (viscosity - 13.8 cpoise under the same conditions).
In many compounds, this element exhibits a valence of +1 (oxidation state), like sodium and other alkali metals. It is usually regarded as analogous to these metals. Accordingly, he heads Group I of the Mendeleev system. In metal hydrides, the hydrogen ion exhibits a negative charge (the oxidation state is -1), that is, Na + H- has a structure similar to Na + Cl- chloride. In accordance with this and some other facts (the closeness of the physical properties of the element "H" and halogens, the ability to replace it with halogens in organic compounds), Hydrogene belongs to the VII group of the Mendeleev system.
Under normal conditions, molecular hydrogen has low activity, combining directly only with the most active non-metals (with fluorine and chlorine, with the latter in the light). In turn, when heated, it interacts with many chemical elements.
Atomic hydrogen has increased chemical activity (when compared with molecular hydrogen). With oxygen, it forms water according to the formula:
Н₂ + ½О₂ = Н₂О,
releasing 285.937 kJ / mol of heat or 68.3174 kcal / mol (25 ° C, 1 atm). Under normal temperature conditions, the reaction proceeds rather slowly, and at t °> = 550 ° C - uncontrollably. The explosive limits of a hydrogen + oxygen mixture by volume are 4–94% H₂, and a hydrogen + air mixture is 4–74% H₂ (a mixture of two volumes of H₂ and one volume of O₂ is called detonating gas).
This element is used to reduce most metals, since it takes oxygen from oxides:
Fe₃O₄ + 4H₂ = 3Fe + 4Н₂О,
CuO + H₂ = Cu + H₂O etc.
With various halogens, hydrogen forms hydrogen halides, for example:
H₂ + Cl₂ = 2HCl.
However, when reacting with fluorine, hydrogen explodes (this also happens in the dark, at -252 ° C), reacts with bromine and chlorine only when heated or illuminated, and with iodine only when heated. When interacting with nitrogen, ammonia is formed, but only on the catalyst, at elevated pressures and temperatures:
ЗН₂ + N₂ = 2NН₃.
When heated, hydrogen actively reacts with sulfur:
Н₂ + S = H₂S (hydrogen sulfide),
and much more difficult - with tellurium or selenium. Hydrogen reacts with pure carbon without a catalyst, but at high temperatures:
2H₂ + C (amorphous) = CH₄ (methane).
This substance directly reacts with some of the metals (alkali, alkaline earth and others), forming hydrides, for example:
Н₂ + 2Li = 2LiH.
The interactions of hydrogen and carbon monoxide (II) are of great practical importance. In this case, depending on the pressure, temperature and catalyst, various organic compounds are formed: НСНО, СН₃ОН, etc. Unsaturated hydrocarbons pass into saturated ones during the reaction, for example:
С n Н₂ n + Н₂ = С n Н₂ n ₊₂.
Hydrogen and its compounds play an exceptional role in chemistry. It determines the acidic properties of the so-called. protic acids, tends to form a hydrogen bond with various elements, which has a significant effect on the properties of many inorganic and organic compounds.
Hydrogen production
The main types of raw materials for the industrial production of this element are refinery gases, natural combustible and coke oven gases. It is also obtained from water through electrolysis (where electricity is available). One of the most important methods for the production of material from natural gas is the catalytic interaction of hydrocarbons, mainly methane, with water vapor (so-called conversion). For example:
СН₄ + H₂О = СО + ЗН₂.
Incomplete oxidation of hydrocarbons with oxygen:
CH₄ + ½O₂ = CO + 2H₂.
The synthesized carbon monoxide (II) undergoes conversion:
CO + H₂O = CO₂ + H₂.
Hydrogen produced from natural gas is the cheapest.
For electrolysis of water, a direct current is used, which is passed through a NaOH or KOH solution (acids are not used to avoid corrosion of the apparatus). In laboratory conditions, the material is obtained by electrolysis of water or as a result of the reaction between hydrochloric acid and zinc. However, more often they use ready-made factory material in cylinders.
From refinery gases and coke oven gas, this element is isolated by removing all other components of the gas mixture, since they liquefy more easily during deep cooling.
This material began to be obtained industrially at the end of the 18th century. Then it was used to fill balloons. At the moment, hydrogen is widely used in industry, mainly in the chemical industry, for the production of ammonia.
Mass consumers of the substance are producers of methyl and other alcohols, synthetic gasoline and many other products. They are obtained by synthesis from carbon monoxide (II) and hydrogen. Hydrogene is used for the hydrogenation of heavy and solid liquid fuels, fats, etc., for the synthesis of HCl, for the hydrotreating of petroleum products, as well as for cutting / welding metals. The most important elements for nuclear energy are its isotopes - tritium and deuterium.
The biological role of hydrogen
About 10% of the mass of living organisms (on average) falls on this element. It is a part of water and the most important groups of natural compounds, including proteins, nucleic acids, lipids, carbohydrates. What is it for?
This material plays a decisive role: in maintaining the spatial structure of proteins (quaternary), in the implementation of the principle of complementarity of nucleic acids (ie, in the implementation and storage of genetic information), in general in "recognition" at the molecular level.
The hydrogen ion H + takes part in important dynamic reactions / processes in the body. Including: in biological oxidation, which provides living cells with energy, in biosynthesis reactions, in photosynthesis in plants, in bacterial photosynthesis and nitrogen fixation, in maintaining acid-base balance and homeostasis, in membrane transport processes. Along with carbon and oxygen, it forms the functional and structural basis of the phenomena of life.
Chemical properties of hydrogen
Under normal conditions, molecular hydrogen is comparatively little active, combining directly only with the most active non-metals (with fluorine, and in the light and 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 temperatures, Hydrogen directly reacts 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 readily decomposed by water to form the corresponding alkali and hydrogen:
Ca H 2 + 2H 2 O = Ca (OH) 2 + 2H 2
- When hydrogen interacts with non-metals volatile hydrogen compounds are formed. In the chemical formula of a volatile hydrogen compound, the hydrogen atom can be in the first or second place, depending on its location in the PSCE (see the plate in the slide):1). With oxygen Hydrogen forms water:
Video "Combustion of hydrogen"
2H 2 + O 2 = 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 oxyhydrogen gas)
.
Video "Explosion of oxyhydrogen gas"
Video "Cooking and explosion of an explosive mixture"
2). With halogens Hydrogen forms hydrogen halides, for example:
H 2 + Cl 2 = 2HCl
At the same time, 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 interacts with the formation of ammonia:
ZN 2 + N 2 = 2NH 3
only on the catalyst and at elevated temperatures and pressures.
4). When heated, Hydrogen reacts vigorously with gray:
H 2 + S = H 2 S (hydrogen sulfide),
it is 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 metal is reduced. Hydrogen - exhibits the properties of a reducing agent:
Hydrogen is used for the recovery of many metals, since it takes oxygen from their oxides:
Fe 3 O 4 + 4H 2 = 3Fe + 4H 2 O, etc.
Application of hydrogen
Video "Application of Hydrogen"
Currently, hydrogen is produced in huge quantities. A very large part of it is used in the synthesis of ammonia, hydrogenation of fats and in the hydrogenation of coal, oils and hydrocarbons. In addition, hydrogen is used for the synthesis of hydrochloric acid, methyl alcohol, hydrocyanic acid, in the welding and forging of metals, as well as in the manufacture of incandescent lamps and precious stones. Hydrogen goes on sale in cylinders under a pressure of over 150 atm. They are colored dark green and have a red inscription "Hydrogen".
Hydrogen is used to convert liquid fats into solid ones (hydrogenation), production of liquid fuels by hydrogenation of coal and fuel oil. In metallurgy, hydrogen is used as a reductant of oxides or chlorides to obtain 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-probes, in the chemical industry it serves as a raw material for obtaining many very important products (ammonia, etc.), in food - for the production of solid fats from vegetable oils, etc. High temperature (up to 2600 ° C), resulting from the combustion of hydrogen in oxygen, is used to melt refractory metals, quartz, etc. Liquid hydrogen is one of the most efficient jet fuels. The annual global consumption of hydrogen exceeds 1 million tons.
Trainers
No. 2. Hydrogen
ASSIGNMENT TASKS
Task number 1Make up the equations for the reactions of hydrogen interaction with the following substances: F 2, Ca, Al 2 O 3, mercury (II) oxide, tungsten (VI) oxide. 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?
Industrial methods for obtaining simple substances depend on the form in which the corresponding element is found in nature, that is, what can be the raw materials for its production. So, oxygen, which is available in a free state, is obtained by a physical method - by separation from liquid air. Almost all hydrogen is in the form of compounds, therefore, chemical methods are used to obtain it. In particular, decomposition reactions can be used. One of the methods for producing hydrogen is the reaction of water decomposition by electric current.
The main industrial method for producing hydrogen is the reaction of methane with water, which is part of natural gas. It is carried out at a high temperature (it is easy to make sure that no reaction occurs when methane is passed even through boiling water):
CH 4 + 2H 2 0 = CO 2 + 4H 2 - 165 kJ
In the laboratory, to obtain simple substances, they do not necessarily use natural raw materials, but select those starting materials from which it is easier to isolate the required substance. For example, in a laboratory, oxygen is not obtained from the air. The same applies to the production of hydrogen. One of the laboratory methods for producing hydrogen, which is sometimes used in industry, is the decomposition of water with an electric current.
Usually in the laboratory, hydrogen is produced by the interaction of zinc with hydrochloric acid.
In industry
1.Electrolysis of aqueous solutions of salts:
2NaCl + 2H 2 O → H 2 + 2NaOH + Cl 2
2.Passing water vapor over hot coke at a temperature of about 1000 ° C:
H 2 O + C ⇄ H 2 + CO
3.Natural gas.
Steam conversion: CH 4 + H 2 O ⇄ CO + 3H 2 (1000 ° C) Catalytic oxidation with oxygen: 2CH 4 + O 2 ⇄ 2CO + 4H 2
4. Cracking and reforming of hydrocarbons in the process of oil refining.
In the laboratory
1.The action of dilute acids on metals. To carry out such a reaction, zinc and hydrochloric acid are most often used:
Zn + 2HCl → ZnCl 2 + H 2
2.Interaction of calcium with water:
Ca + 2H 2 O → Ca (OH) 2 + H 2
3.Hydrolysis of hydrides:
NaH + H 2 O → NaOH + H 2
4.The action of alkalis on zinc or aluminum:
2Al + 2NaOH + 6H 2 O → 2Na + 3H 2 Zn + 2KOH + 2H 2 O → K 2 + H 2
5.By electrolysis. During the electrolysis of aqueous solutions of alkalis or acids, hydrogen is evolved at the cathode, for example:
2H 3 O + + 2e - → H 2 + 2H 2 O
- Bioreactor for hydrogen production
Physical properties
Gaseous hydrogen can exist in two forms (modifications) - in the form of ortho - and para-hydrogen.
In a molecule of orthohydrogen (mp -259.10 ° C, bp b. -252.89 ° C) - opposite to each other (antiparallel).
Allotropic forms of hydrogen can be separated by adsorption on active carbon at liquid nitrogen temperature. At very low temperatures, the equilibrium between orthohydrogen and parahydrogen is almost entirely shifted towards the latter. At 80 K, the ratio of forms is approximately 1: 1. When heated, desorbed parahydrogen is converted into orthohydrogen until a mixture equilibrium at room temperature is formed (ortho-pair: 75:25). Without a catalyst, the transformation is slow, which makes it possible to study the properties of individual allotropic forms. The hydrogen molecule is diatomic - Н₂. Under normal conditions, it is a colorless, odorless and tasteless gas. Hydrogen is the lightest gas, its density is many times less than that of air. It is obvious that the smaller the mass of the molecules, the higher their speed at the same temperature. As the lightest, hydrogen molecules move faster than molecules of any other gas and thus can transfer heat faster from one body to another. It follows that hydrogen has the highest thermal conductivity among gaseous substances. Its thermal conductivity is about seven times higher than the thermal conductivity of air.
Chemical properties
Hydrogen molecules H₂ are quite strong, and in order for hydrogen to react, a lot of energy must be expended: H 2 = 2H - 432 kJ Therefore, at ordinary temperatures, hydrogen reacts only with very active metals, for example, with calcium, forming calcium hydride: Ca + H 2 = CaH 2 and with the only non-metal - fluorine, forming hydrogen fluoride: F 2 + H 2 = 2HF With most metals and non-metals, hydrogen reacts at elevated temperatures or under another action, for example, under lighting. It can "take away" oxygen from some oxides, for example: CuO + H 2 = Cu + H 2 0 The written equation reflects the reduction reaction. Reduction reactions are the processes in which oxygen is taken away from the compound; substances that take away oxygen are called reducing agents (while they themselves are oxidized). Further, another definition of the concepts "oxidation" and "reduction" will be given. And this definition, historically the first, retains its significance at the present time, especially in organic chemistry. The reduction reaction is the opposite of the oxidation reaction. Both of these reactions always proceed simultaneously as one process: during the oxidation (reduction) of one substance, the reduction (oxidation) of the other must necessarily occur simultaneously.
N 2 + 3H 2 → 2 NH 3
Forms with halogens hydrogen halides:
F 2 + H 2 → 2 HF, the reaction proceeds with an explosion in the dark and at any temperature, Cl 2 + H 2 → 2 HCl, the reaction proceeds with an explosion, only in the light.
Reacts with soot under strong heating:
C + 2H 2 → CH 4
Interaction with alkali and alkaline earth metals
Hydrogen forms with active metals hydrides:
Na + H 2 → 2 NaH Ca + H 2 → CaH 2 Mg + H 2 → MgH 2
Hydrides- salty, solid substances, easily hydrolyzed:
CaH 2 + 2H 2 O → Ca (OH) 2 + 2H 2
Interaction with metal oxides (usually d-elements)
Oxides are reduced to metals:
CuO + H 2 → Cu + H 2 O Fe 2 O 3 + 3H 2 → 2 Fe + 3H 2 O WO 3 + 3H 2 → W + 3H 2 O
Hydrogenation of organic compounds
When hydrogen acts on unsaturated hydrocarbons in the presence of a nickel catalyst and an elevated temperature, a reaction occurs hydrogenation:
CH 2 = CH 2 + H 2 → CH 3 -CH 3
Hydrogen reduces aldehydes to alcohols:
CH 3 CHO + H 2 → C 2 H 5 OH.
Hydrogen Geochemistry
Hydrogen is the basic building block of the universe. It is the most abundant element, and all elements are formed from it as a result of thermonuclear and nuclear reactions.
Free hydrogen H 2 is relatively rare in terrestrial gases, but in the form of water it plays an extremely important role in geochemical processes.
Hydrogen can be included in minerals in the form of ammonium ion, hydroxyl ion and crystal water.
In the atmosphere, hydrogen is continuously formed as a result of the decomposition of water by solar radiation. It migrates to the upper atmosphere and escapes into space.
Application
- Hydrogen energy
Atomic hydrogen is used for atomic hydrogen welding.
In the food industry, hydrogen is registered as a food additive E949 like packing gas.
Features of treatment
When mixed with air, hydrogen forms an explosive mixture - the so-called explosive gas. This gas is most explosive when the volume ratio of hydrogen and oxygen is 2: 1, or hydrogen and air is approximately 2: 5, since the air contains about 21% oxygen. Hydrogen is also fire hazardous. Liquid hydrogen can cause severe frostbite if it comes into contact with the skin.
Explosive concentrations of hydrogen with oxygen occur from 4% to 96% by volume. When mixed with air from 4% to 75 (74)% by volume.
Use of hydrogen
In the chemical industry, hydrogen is used in the production of ammonia, soap and plastics. In the food industry, margarine is made from liquid vegetable oils using hydrogen. Hydrogen is very light and always rises up in the air. Once airships and balloons were filled with hydrogen. But in the 30s. XX century. there have been several horrific disasters as the airships exploded and burned. Nowadays, airships are filled with helium gas. Hydrogen is also used as rocket fuel. Hydrogen may someday be widely used as a fuel for cars and trucks. Hydrogen engines do not pollute the environment and only emit water vapor (however, the very production of hydrogen leads to some environmental pollution). Our sun is mostly made of hydrogen. Solar heat and light are the result of the release of nuclear energy from the fusion of hydrogen nuclei.
Using hydrogen as fuel (economic efficiency)
The most important characteristic of substances used as fuel is their calorific value. It is known from the course of general chemistry that the reaction of interaction of hydrogen with oxygen occurs with the release of heat. If we take 1 mol of H 2 (2 g) and 0.5 mol of O 2 (16 g) under standard conditions and initiate a reaction, then according to the equation
H 2 + 0.5 O 2 = H 2 O
after the completion of the reaction, 1 mol of H 2 O (18 g) is formed with an energy release of 285.8 kJ / mol (for comparison: the heat of combustion of acetylene is 1300 kJ / mol, propane is 2200 kJ / mol). 1 m³ of hydrogen weighs 89.8 g (44.9 mol). Therefore, to obtain 1 m³ of hydrogen, 12832.4 kJ of energy will be spent. Taking into account that 1 kWh = 3600 kJ, we get 3.56 kWh of electricity. Knowing the tariff for 1 kWh of electricity and the cost of 1 m³ of gas, it can be concluded that it is advisable to switch to hydrogen fuel.
For example, an experimental model of the 3rd generation Honda FCX with a 156 liter hydrogen tank (contains 3.12 kg of hydrogen under a pressure of 25 MPa) travels 355 km. Accordingly, from 3.12 kg H2, 123.8 kWh is obtained. Energy consumption per 100 km will be 36.97 kWh. Knowing the cost of electricity, the cost of gas or gasoline, their consumption for a car per 100 km, it is easy to calculate the negative economic effect of switching cars to hydrogen fuel. Say (Russia 2008), 10 cents per kWh of electricity leads to the fact that 1 m³ of hydrogen leads to a price of 35.6 cents, and taking into account the efficiency of water decomposition of 40-45 cents, the same amount of kWh from burning gasoline costs 12832.4kJ / 42000kJ / 0.7kg / l * 80 cents / l = 34 cents at retail prices, while for hydrogen we calculated the ideal option, excluding transportation, equipment depreciation, etc. For methane with a combustion energy of about 39 MJ per m³ the result will be two to four times lower due to the difference in price (1m³ for Ukraine costs $ 179, and for Europe $ 350). That is, the equivalent amount of methane will cost 10-20 cents.
However, we should not forget that when hydrogen is burned, we get pure water, from which it was extracted. That is, we have a renewable storehouse energy without harm to the environment, unlike gas or gasoline, which are the primary sources of energy.
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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 about the physical properties of simple substances they form, learn more about the role of oxygen and hydrogen in nature and life person.
Hydrogen- the most common element in the universe. Oxygen- the most abundant element on Earth. Together they form water - a substance that makes up more than half the mass of the human body. Oxygen is a gas that we need for breathing, and without water we could not live for several days, so oxygen and hydrogen can undoubtedly be considered the most important chemical elements necessary for life.
The structure of hydrogen and oxygen atoms
Thus, hydrogen exhibits non-metallic properties. In nature, hydrogen occurs in the form of three isotopes, protium, deuterium and tritium, the isotopes of hydrogen 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, which results in the presence of several isotopes in one element, 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 bond 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 a higher electronegativity value), 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 the less electronegative atom and the other bond with fluorine, it will be in the 0 oxidation state.
Physical properties of hydrogen and oxygen, oxygen allotropy
Hydrogen- a colorless, odorless and tasteless gas. 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- a colorless gas, odorless and tasteless, slightly heavier than air. At a temperature of -182.9 ° C it turns into a heavy blue liquid, at -218 ° C it solidifies with the formation of blue crystals. Oxygen molecules are paramagnetic, meaning oxygen is attracted by 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 production of 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.
From a chemical point of view, hydrogen is a typical non-metal. That is, it is capable of interacting 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 with hydrogen directly, its hydride is obtained by exchange reactions.
Hydrogen also reacts with non-metals only when heated. Exceptions are chlorine and bromine halogens, the reaction with which can be induced by light:
.
The reaction with fluorine also does not require heating; it proceeds explosively 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 with hydrogen in a ratio of 1: 2, the reaction proceeds with an explosion (such a mixture is called "detonating gas"):
.
The reaction with sulfur proceeds much more calmly, with practically no heat release:
.
Reactions with nitrogen and iodine are reversible:
,
.
This circumstance greatly complicates the production of ammonia in industry: the process requires the use of increased pressure to mix the equilibrium towards the formation of ammonia. Hydrogen iodide is not obtained by direct synthesis, since there are several much more convenient methods for its synthesis.
Hydrogen does not react directly 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-activity metals (located after hydrogen in a 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 is needed for this:
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Metals that are more active than zinc are almost impossible to reduce with hydrogen.
In the laboratory, hydrogen is produced by the interaction of 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 obtained as a by-product in the production of caustic soda by electrolysis of a sodium chloride solution:
In addition, hydrogen is obtained from petroleum refining.
The production of hydrogen by photolysis of water is one of the most promising methods in the future, but at the moment the industrial application of this method is difficult.
Work with the materials of electronic educational resources. Laboratory work "Obtaining and properties of hydrogen" and Laboratory work "Reducing properties of hydrogen". Study 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 show 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 without heating reacts with active metals (alkali, alkaline earth and some lanthanides):
When heated, oxygen interacts with most metals to form oxides:
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Silver and less active metals are not oxidized by oxygen.
Oxygen also reacts with most non-metals to form oxides:
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It interacts with nitrogen 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:
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Oxygen (II) fluoride is an unstable compound, easily decomposes and is 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 behind hydrogen in a series of voltages:
When heated, oxygen can oxidize lower metal oxides:
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Oxygen is not produced in industry by chemical methods; it is obtained from air by distillation.
The laboratory uses the 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 generate oxygen.
Work with the materials of the electronic educational resource. Laboratory work "Obtaining 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 "Decomposition of potassium permanganate on heating."
Answer the questions:
- Which of the solid reaction products is soluble in water?
- What color is potassium permanganate solution?
- What is the color of the potassium manganate solution?
Write down the equations of the reactions taking place. Equalize them using the electronic balance method.
Discuss the assignment with the teacher in 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 nitrogen oxide (IV) to nitrogen oxide (V), and sulfur oxide (IV) to sulfur oxide (VI) without a catalyst:
Ozone gradually decomposes to form oxygen:
To obtain ozone, special devices are used - ozonizers, in which a glow discharge is passed through oxygen.
In the laboratory, to obtain small amounts of ozone, sometimes decomposition reactions of peroxo compounds and some higher oxides are used when heated:
Work with the materials of the electronic educational resource. Laboratory work "Obtaining ozone and the study of its properties."
Explain why the indigo solution is discolored. 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. For the ion exchange reaction, write the ionic equations. For a redox reaction, draw up an electronic balance.
Discuss the assignment with the teacher in or in the video room.
Chemical properties of water
For a better acquaintance with the physical properties of water and its significance, work with the materials of the electronic educational resources "Anomalous properties of water" and "Water is the most important liquid on Earth."
Water is of great importance for all living organisms - in fact, many living organisms consist of more than half of 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 an aqueous solution it dissociates (albeit to a very small extent) into hydrogen cations and hydroxide anions:
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Water interacts with many metals. With active (alkaline, alkaline earth and some lanthanides) water reacts without heating:
Interaction with less active occurs when heated.
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