Equation without changing the degree of oxidation of NaBr. Extracurricular lesson - Redox reactions. A reactions in which the degree of oxidation of the elements does not change

Redox reactions include such that accompanied by the movement of electrons from some particles to the other. When considering the patterns of the flow of redox reactions, the concept of oxidation is used.

Degree of oxidation

Concept oxidation degree Entered to characterize the status of elements in connections. Under the degree of oxidation is understood The conditional charge of an atom in the compound calculated on the basis of the assumption that the connection consists of ions. The degree of oxidation is denoted by the Arabic number with a plus sign when displaced electrons from a given atom to another atom and a digit with a minus sign when electron displaced in the opposite direction. The digit with the "+" or "-" sign is set over the element symbol. The degree of oxidation indicates the state of the oxidation of an atom and represents only a convenient form for taking into account electron transfer: it should not be considered as an effective charge of an atom in the molecule (for example, in the LIF molecule, effective charges Li and F are equal, respectively + 0.89 and -0, 89, whereas the degrees of oxidation +1 and -1), nor as the valence of the element (for example, in compounds CH 4, CH 3 OH, HCOOH, CO 2, carbon valence is 4, and the degree of oxidation is respectively - 4, -2, + 2, +4). The numerical values \u200b\u200bof the valence and degrees of oxidation may coincide in absolute value only when the compounds are for the ionic structure.

When determining the degree of oxidation, the following rules use:

Atoms of elements that are in free state or in the form of molecules of simple substances have a degree of oxidation equal to zero, for example Fe, Cu, H 2, N 2, and the like.

The degree of oxidation of the element in the form of a single andatomy ion in a compound having an ion structure is equal to the charge of this ion,

1 -1 +2 -2 +3 -1

for example, NaCl, Cu S, Alf 3.

Hydrogen in most compounds has an oxidation degree of +1, with the exception of metal hydrides (NAH, LIH), in which the degree of hydrogen oxidation is -1.

The most common degree of oxidation of oxygen in compounds -2, with the exception of peroxides (Na 2 O 2, H 2 O 2), in which the degree of oxidation of oxygen is -1 and F 2 O, in which the degree of oxidation of oxygen is +2.

For elements with a non-permanent degree of oxidation, it can be calculated, knowing the compound formula and considering that the algebraic sum of the oxidation of all elements in the neutral molecule is zero. In a complex ion, this amount is equal to the charge of an ion. For example, the degree of oxidation of the chlorine atom in the HCLO 4 molecule, calculated on the basis of the total charge of the molecule \u003d 0, where x is the degree of oxidation of the chlorine atom), is +7. The degree of oxidation of the sulfur atom in ion (SO 4) 2- [x + 4 (-2) \u003d -2] is +6.

Redox properties of substances

Any oxidation reaction consists of oxidation and recovery processes. Oxidation - this is the process of recoil electron atom, ion or a reagent molecule. Substances that give its electrons in the process of reaction and at the same time are oxidized, called reducing agents.

Recovery is the process of adopting electrons atom, ion or reagent molecule.

Substances that accept electrons are restored, called oxidizing agents.

Reactions of reduction oxidation always proceed as a single process called redox reaction. For example, with the interaction of metal zinc with copper ions reducing agent (Zn) gives his electrons oxidizer- copper ions (Cu 2+):

Zn + Cu 2+ Zn 2+ + Cu

Copper stands out on the zinc surface, and zinc ions are moving into the solution.

The redox properties of the elements are associated with the structure of their atoms and are determined by the provision in the periodic system D.I. Mendeleeva. The reduction capacity of the element is due to the weak bond of valence electrons with the kernel. Metal atoms containing a small number of electrons in the external energy level are prone to their return, i.e. Easily oxidized, playing the role of reducing agents. The strongest reducing agents are the most active metals.

The criterion of the redox activity of the elements can be the value of them relative electronegitability: What it is higher, the stronger the oxidative ability of the element is expressed, and the lower, the brighter its regenerative activity is manifested. Non-metal atoms (for example, F, O) have a high value of the affinity for an electron and relative electronegativity, they easily accept electrons, i.e. are oxidants.

The redox properties of the element depends on the degree of its oxidation. The same element distinguish low, highest and intermediate degrees of oxidation.

As an example, consider the sulfur S and its compound H 2 S, SO 2 and SO 3. The relationship between the electronic structure of the sulfur atom and its redox properties in these compounds is clearly presented in Table 1.

In the H 2 S molecule, the sulfur atom has a stable octet configuration of the external energy level 3S 2 3P 6 and therefore can no longer connect the electrons, but can give them.

The state of the atom in which it can no longer take electrons, is called the lowest degree of oxidation.

In the lowest oxidation, the atom loses the oxidative ability and can only be a reducing agent.

Table 1.

Formula of substances	Electronic formula	Redox Properties
	1S 2 2S 2 2P 6 3S 2 3P 6	–2 ; - 6 ; - 8 reducing agent
	1S 2 2S 2 2P 6 3S 2 3P 4	+ 2 oxidizing agent	–4 ; - 6 reducing agent
	1S 2 2S 2 2P 6 3S 2 3P O	+ 4 ; + 6 oxidizing agent	-2 reducing agent
	1S 2 2S 2 2P 6 3S O 3P 0	+ 2 ; + 6 ; + 8 oxidizing agent

In the SO 3 molecule, all external electrons of the sulfur atom are shifted to oxygen atoms. Consequently, in this case, the sulfur atom can only take electrons, showing oxidative properties.

The state of the atom in which he gave all the valence electrons is called the highest degree of oxidation.Atom, which is in the highest oxidation, can only be an oxidizer.

In the SO 2 molecule and elementary gray s sulfur atom is in intermediate degrees of oxidation, i.e., having valence electrons, the atom can give them, but without having a complete r -subject, may and receive electrons before it is completed.

An atom of an element having an intermediate degree of oxidation may exhibit both oxidative and reducing properties, which is determined by its role in a specific reaction.

So, for example, the role of sulfite - anion SO the following reactions are different:

5NA 2 SO 3 + 2KMNO 4 + 3H 2 SO 4  2MNSO 4 + 5NA 2 SO 4 + K 2 SO 4 + 3H 2 O (1)

H 2 SO 3 + 2 H 2 S  3 S + 3 H 2 O (2)

In the reaction (1) sulfite anion SO in the presence of a strong oxidantkmno 4 plays the role of the reducing agent; In the reaction (2) sulfite anion SO - oxidizing agent, since H 2 S can only be rehabilitating properties.

Thus, among complex substances restores may be:

1. Simple substances whose atoms have low ionization and electronegability energy values \u200b\u200b(in particular metals).

2. Complex substances containing atoms in the lower degrees of oxidation:

H. Cl., H 2. S.,N.H 3.

Na 2. S.O 3 FE.CL 2, SN.(NO 3) 2.

Oxidifiersmay be:

1. Simple substances whose atoms have high incidence affinity and electronegability - non-metals.

2. Complex substances containing atoms in the highest degrees of oxidation: +7 +6 +7

K. MN.O 4, k 2 CR 2 O 7, HCLO 4.

3. Complex substances containing atoms in intermediate degrees of oxidation:

Na 2. S.O 3 MN.O 2 MN.SO 4.

One of the main concepts inorganic chemistry is the concept of oxidation degree (CO).

The degree of oxidation of the element in the compound is a formal charge of an element atom calculated from the assumption that valence electrons go to atoms with greater relative electronegitability (OEO) and all connections in the compound molecule are ionic.

The degree of oxidation of the element e point above the symbol of the element with the "+" or "-" sign in front of the digit.

The degree of oxidation of ions, actually existing in solution or crystals, coincides with their charge number and is indicated similarly to the "+" or "" or "" sign, for example, Ca 2+.

The method of the rim design of the degree of oxidation of Roman numbers after the element symbol is also used: Mn (VII), Fe (III).

The question of the sign of the degree of oxidation of atoms in the molecule is solved on the basis of comparison of electronegatenes related to among themselves, which form a molecule. In this case, an atom with less electronegitivity has a positive degree of oxidation, and with greater electronegitability is negative.

It should be noted that it is impossible to identify the degree of oxidation with the valence of the element. Valence defined as a number chemical tiesWith which this atom is connected to other atoms, cannot be zero and does not have a "+" or "" sign. The degree of oxidation can have both positive and negative value, as well as take zero and even fractional value. Thus, in the CO 2 molecule, the degree of oxidation C is +4, and in the CH molecule 4, the degree of oxidation C is equal to 4. The valence of carbon and in that, and in another compound it is equal to IV.

Despite the above disadvantages, the use of the concept of oxidation is convenient when classifying chemical compounds and the preparation of equations of redox reactions.

Two interrelated processes occur during oxidative reaction reactions: oxidation and recovery.

Oxidation The process of electron loss is called. Restoration The process of connecting electrons.

Substances, atoms or ions of which give electrons, are called reducing agents. Substances, atoms or ions of which attach electrons (or delayed a common pair of electrons), are called oxidifiers.

When the element is oxidized, the degree of oxidation increases, in other words, the reducing agent increases the degree of oxidation.

On the contrary, when the element is restored, the degree of oxidation decreases, i.e., during the reaction, the oxidant reduces the degree of oxidation.

Thus, it is possible to give such a formulation of redox reactions: oxidative-reducing reactions are called reactions flowing with a change in the degree of oxidation of the atoms of elements that are part of the reacting substances.

Oxidifiers and reducing agents

To predict the products and directions of redox reactions, it is useful to remember that typical oxidants are simple substances whose atoms have a large OEO\u003e 3.0 (VIIA elements and viia groups). Of these, the strongest fluorine oxidants (OEO \u003d 4.0), oxygen (OEO \u003d 3.0), chlorine (OEO \u003d 3.5). An important oxidizers include PBO 2, KMNO 4, CA (SO 4) 2, to 2 CR 2 O 7 , HCLO, HCLO 3, CCO 4, Nabio 3, H 2 SO4 (concludes), HNO 3 (concludes), Na 2 O 2, (NH 4) 2 S 2 O 8, KSIO 3, H 2 O 2 and other substances that contain atoms with high or high CO.

Typical reducing agents include simple substances whose atoms have a small OEO< 1,5 (металлы IA и IIAгрупп и некоторые другие металлы). К важным восстановителям относятся H 2 S, NH 3 , HI, KI, SnCl 2 , FeSO 4 , C, H 2 , CO, H 2 SO 3 , Cr 2 (SO 4) 3 , CuCl, Na 2 S 2 O 3 и другие вещества, которые содержат атомы с низкими СО.

In the preparation of equations of redox reactions, two methods can be applied: the electronic balance method and the ion-electronic method (half-formation method). A more correct idea of \u200b\u200boxidative and reducing processes in solutions is given by an ion-electronic method. Using this method, changes are predicted that undergo actually existing in the solution of ions and molecules.

In addition to predicting the reaction products, the ionic equations of half-formations are necessary to understand the redox processes occurring under electrolysis and in electroplating elements. This method reflects the role of the environment as a participant in the process. Finally, when using this method, it is not necessary to know all the formed substances in advance, since many of them are obtained in the preparation of the equation of redox reactions.

It should be borne in mind that although half-reaction reflects the real processes going on with oxidative reaction reactions, they cannot be identified with real stages (mechanism) of redox reactions.

Many factors are influenced by the nature and direction of redox reactions: the nature of the reactant substances, the reaction of the medium, concentration, temperature, catalysts.

Biological significance of redox processes

An important processes in animal organisms are the reactions of enzymatic oxidation of substances - substrates: carbohydrates, fats, amino acids. As a result of these processes, organisms receive a large amount of energy. Approximately 90% of the entire need for an adult man in energy is covered due to the energy produced in tissues in the oxidation of carbohydrates and fats. The remaining part of the energy is ~ 10% gives the oxidative splitting of amino acids.

Biological oxidation proceeds through complex mechanisms with the participation of a large number of enzymes. In mitochondria, oxidation occurs as a result of electron transfer from organic substrates. The electron carriers in the respiratory chain mitochondria include various proteins containing a variety functional groupswhich are designed to transfer electrons. As the chain progresses from one intermediate to another electrons lose free energy. On each pair of electrons transmitted in the respiratory chain oxygen, 3 ATP molecules are synthesized. The free energy released during the transfer of 2 electrons per oxygen is 220 kJ / mol.

The synthesis of 1 ATP molecules under standard conditions are consumed by 30.5 kJ. It is clear from here that a fairly significant part of the free energy released during the transfer of one pair of electrons is covered in ATP molecules. From this data, the role of multistage transmission of electrons from the initial reducing agent to oxygen becomes clear. A large energy (220 kJ), allocated when transferring one pair of electrons to oxygen, is divided into a number of servings corresponding to individual stages of oxidation. At three such stages, the amount of energy released approximately corresponds to the energy required for the synthesis of 1 ATP molecules.

Definition

Degree of oxidation - this is a quantitative assessment of the state of the atom chemical element In the compound based on its electronegability.

It takes both positive and negative values. To specify the degree of oxidation of the element in the connection, it is necessary to put on top above its symbol of the Arabic digit with the corresponding sign ("+" or "-").

It should be remembered that the degree of oxidation is a value that does not have a physical meaning, since it does not reflect the actual charge of the atom. However, this concept is very widely used in chemistry.

Table of the degree of oxidation of chemical elements

The maximum positive and minimum negative degree of oxidation can be determined by Periodic table DI. Mendeleeva. They are equal to the number of the group in which the element is located, and the difference between the "highest" value of oxidation and number 8, respectively.

If we consider chemical compounds more specifically, then in substances with non-polar connections The degree of oxidation of the elements is zero (N 2, H 2, CL 2).

The degree of metal oxidation in the elementary state is zero, since the distribution of electron density in them is uniformly.

In ordinary ionic compounds, the degree of oxidation of the elements included in them is equal to the electrical charge, since the formation of these compounds there is an almost complete transition of electrons from one atom to another: Na +1 i -1, Mg +2 Cl -1 2, Al +3 F - 1 3, Zr +4 BR -1 4.

In determining the degree of oxidation of elements in compounds with polar covalent bonds, they compare the values \u200b\u200bof their electrical negotiations. Since, in the formation of chemical bond, electrons are shifted to atoms of more electronegative elements, the latter have a negative degree of oxidation in compounds.

There are elements for which only one oxidation degree value (fluorine, IA metals and IIA groups, etc.). Fluoro characterizes the greatest value Electricity, in compounds always has a constant negative degree of oxidation (-1).

Alkaline and alkaline earth elements for which there is a relatively low value of electronegativity, always have a positive degree of oxidation equal to (+1) and (+2).

However, there are also such chemical elements for which several oxidation degree (sulfur - (-2), 0, (+2), (+4), (+6), etc.).

In order to make it easier to remember how many and how oxidation degrees are characteristic of a specific chemical element use tables of degrees of oxidation of chemical elements that look like this:

Serial number	Russian / English name	Chemical symbol	Degree of oxidation
	Hydrogen / Hydrogen.
	Helium / Helium.
	Lithium / Lithium.
	Beryllius / Beryllium.
			(-1), 0, (+1), (+2), (+3)
	Carbon / Carbon.		(-4), (-3), (-2), (-1), 0, (+2), (+4)
	Nitrogen / Nitrogen.		(-3), (-2), (-1), 0, (+1), (+2), (+3), (+4), (+5)
	Oxygen / Oxygen.		(-2), (-1), 0, (+1), (+2)
	Fluorine / Fluorine.
	Sodium / sodium
	Magnesium / Magnesium.
	Aluminum / Aluminum.
	Silicon / Silicon.		(-4), 0, (+2), (+4)
	Phosphorus / Phosphorus.		(-3), 0, (+3), (+5)
	Sere / Sulfur.		(-2), 0, (+4), (+6)
	Chlorine / Chlorine		(-1), 0, (+1), (+3), (+5), (+7), rarely (+2) and (+4)
	Argon / Argon.
	Potassium / Potassium.
	Calcium / Calcium
	Scandium / Scandium.
	Titanium / Titanium.		(+2), (+3), (+4)
	Vanadium / Vanadium.		(+2), (+3), (+4), (+5)
	Chrome / Chromium.		(+2), (+3), (+6)
	Manganese / manganese		(+2), (+3), (+4), (+6), (+7)
	Iron / Iron.		(+2), (+3), rarely (+4) and (+6)
	Cobalt / Cobalt.		(+2), (+3), rare (+4)
	Nickel / Nickel		(+2), rarely (+1), (+3) and (+4)
	Copper / Copper.		+1, +2, rarely (+3)
	Gallium / Gallium.		(+3), rarely (+2)
	Germany / germanium.		(-4), (+2), (+4)
	Arsenic / Arsenic		(-3), (+3), (+5), rare (+2)
	Selenium / Selenium.		(-2), (+4), (+6), rare (+2)
	Brom / Bromine		(-1), (+1), (+5), rarely (+3), (+4)
	Crypton / Krypton.
	Rubidium / Rubidium.
	Strontium / strontium
	Yttrium / yttrium
	Zirconium / Zirconium.		(+4), rarely (+2) and (+3)
	Niobium / Niobium		(+3), (+5), rarely (+2) and (+4)
	Molybdenum / Molybdenum		(+3), (+6), rarely (+2), (+3) and (+5)
	Technetium / TechNetium
	Ruthenium / Ruthenium.		(+3), (+4), (+8), rarely (+2), (+6) and (+7)
	Rhodium / rhodium		(+4), rarely (+2), (+3) and (+6)
	Palladium / Palladium.		(+2), (+4), rare (+6)
	Silver / Silver.		(+1), rarely (+2) and (+3)
	Cadmium / Cadmium.		(+2), rarely (+1)
	Indium / Indium.		(+3), rarely (+1) and (+2)
	Tin / Tin.		(+2), (+4)
	Antimony / antimony		(-3), (+3), (+5), rarely (+4)
	Tellur / Tellurium.		(-2), (+4), (+6), rare (+2)
			(-1), (+1), (+5), (+7), rare (+3), (+4)
	Xenon / Xenon
	Cesium / Cesium.
	Barium / Barium.
	Lantan / Lanthanum
	Cerium / Cerium.		(+3), (+4)
	Praseodyodim / praseodymium
	Neodymium / neodymium		(+3), (+4)
	VEMETY / PROMETHIUM.
	Samarium / Samarium.		(+3), rarely (+2)
	European / Europium.		(+3), rarely (+2)
	Gadolini / Gadolinium.
	Terbium / Terbium		(+3), (+4)
	Disposions / Dysprosium.
	Holmium / Holmium.
	Erbium / Erbium
	Tulia / Thulium		(+3), rarely (+2)
	Intrbium / ytterbium		(+3), rarely (+2)
	Lutetius / Lutetium.
	Hafny / Hafnium.
	Tantalum / Tantalum		(+5), rarely (+3), (+4)
	Tungsten / Tungsten.		(+6), rarely (+2), (+3), (+4) and (+5)
	Rhenium		(+2), (+4), (+6), (+7), rarely (-1), (+1), (+3), (+5)
	Osmium / Osmium.		(+3), (+4), (+6), (+8), rare (+2)
	Iridium / Iridium.		(+3), (+4), (+6), rarely (+1) and (+2)
	Platinum / platinum		(+2), (+4), (+6), rarely (+1) and (+3)
	Gold / Gold.		(+1), (+3), rare (+2)
	Mercury / Mercury.		(+1), (+2)
	Talius / Thallium.		(+1), (+3), rare (+2)
	Lead.		(+2), (+4)
	Bismuth / Bismuth.		(+3), rarely (+3), (+2), (+4) and (+5)
	Polonium / Polonium.		(+2), (+4), rarely (-2) and (+6)
	Astat / Astatine.
	Radon / Radon
	France / Francium.
	Radii / Radium
	Actinium / Actinium.
	Thorium / Thorium
	OverTine / protactinium
	Uranium / Uranium		(+3), (+4), (+6), rarely (+2) and (+5)

Examples of solving problems

Example 1.

Answer We will alternately determine the degree of phosphorus oxidation in each of the proposed transform schemes, and then choose the correct answer.

• The degree of oxidation of phosphorus in phosphine is (-3), and in orthophosphoric acid - (+5). Change the degree of phosphorus oxidation: +3 → +5, i.e. The first answer is.
• The degree of oxidation of the chemical element in a simple substance is zero. The degree of oxidation of phosphorus in the composition oxide P 2 O 5 is equal to (+5). Change the degree of phosphorus oxidation: 0 → +5, i.e. Third response option.
• The degree of oxidation of phosphorus in the acid composition of HPO 3 is equal to (+5), and H 3 PO 2 - (+1). Changes in the degree of phosphorus oxidation: +5 → +1, i.e. Fifth answer option.

Example 2.

The task	The degree of oxidation (-3) carbon has in conjunction: a) CH 3 Cl; b) C 2 H 2; c) HCOH; d) C 2 H 6.
Decision	In order to give a sure answer to the question, we will alternately determine the degree of carbon oxidation in each of the proposed compounds. a) The degree of hydrogen oxidation is equal to (+1), and chlorine - (-1). We will take for "x" the degree of carbon oxidation: x + 3 × 1 + (-1) \u003d 0; The answer is incorrect. b) the degree of hydrogen oxidation is equal to (+1). We will take a "y" degree of carbon oxidation: 2 × + 2 × 1 \u003d 0; The answer is incorrect. c) The degree of hydrogen oxidation is equal to (+1), and oxygen - (-2). We will take for "z" the degree of carbon oxidation: 1 + z + (-2) +1 \u003d 0: The answer is incorrect. d) the degree of hydrogen oxidation is equal to (+1). We will take for "a" the degree of carbon oxidation. 2 × a + 6 × 1 \u003d 0; The right answer.
Answer	Option (g)

The chemical reaction is called the process, as a result of which the starting materials are converted into reaction products. Substances obtained after the end of the reaction are called products. From the initial they may differ in the structure, composition or both, and others.

According to the change in the composition, the following types chemical reactions:

• with a change in composition (such major);
• without changing the composition (isomerization and transformation of one allotropic modification to another).

If the composition of the substance does not change as a result of the reaction, then its structure must be changed, for example: CHRAFITSCALMAZ

Consider in more detail the classification of chemical reactions occurring with a change in the composition.

I. In terms of the number and composition of substances

Connection reactions

As a result of such chemical processes, one of several substances is formed: a + in + ... \u003d with

Connects can:

• simple substances: 2NA + S \u003d Na2S;
• simple with complex: 2SO2 + O2 \u003d 2SO3;
• two complex: Cao + H2O \u003d Ca (OH) 2.
• more than two substances: 4Fe + 3O2 + 6H2O \u003d 4FE (OH) 3

Reaction decomposition

One substance in such reactions is decomposed into several others: a \u003d B + C + ...

Products in this case can be:

• simple substances: 2nacl \u003d 2NA + CL2
• simple and complex: 2KnO3 \u003d 2KnO2 + O2
• two complex: Caco3 \u003d Cao + CO2
• more than two products: 2AGNO3 \u003d 2AG + O2 + 2NO2

Reactions of substitution

Such reactions in which the simple and complex substance react with each other, and the atoms of the simple substance replace the atoms of one of the elements in the complex, and is called reactions of substitution. Schematically, the process of replacement of atoms can be represented as follows: a + sun \u003d B + speavers.

For example, Cuso4 + Fe \u003d Feso4 + Cu

Exchange reactions

This group includes reactions during which two sophisticated substances Change with their parts: AV + CD \u003d AD + CB. According to Burtoll rule, irreversible flow of such reactions is possible if at least one of the products:

• specta (insoluble substance): 2NAOH + CUsO4 \u003d Cu (OH) 2 + Na2SO4;
• malodissue substance: NaOH + HCl \u003d NaCl + H2O;
• gas: NaOH + NH4Cl \u003d NaCl + NH3 + H2O (first form ammonia hydrate NH3 H2O, which, when received, immediately decomposes on ammonia and water).

II. On thermal effect

1. Exothermic - Processes leaking with heat release:
   C + O2 \u003d CO2 + Q
2. Endothermic - reactions in which heat is absorbed:
   Cu (OH) 2 \u003d Cuo + H2O - Q

III. Types of chemical reactions in the direction

1. Reversible Called reactions flowing into the same point in time both in direct and in the opposite direction: N2 + O2 ↔ 2NO
2. Irreversible The processes proceed to the end, that is, until at least one of the reacting substances is completely completely. Examples of irreversible exchange reactions were considered above.

IV. By the presence of catalyst

V. According to the aggregative state of substances

1. If all reactants are in the same aggregate states, reaction is called homogenic . Processes occur in all volumes. For example: NaOH + HCl \u003d NaCl + H2O
2. Heterogeneous They call the reactions between substances that are in different aggregate states flowing on the surface of the phase section. For example: Zn + 2HCl \u003d ZnCl2 + H2

Vi. Types of chemical reactions to change the degree of oxidation of reacting substances

1. Oxidative and recovery (ORP) - reactions in which the degrees of oxidation of reactants are changed.
2. Reactions leaking without changing oxidation degrees reagents (BISO).

Always redox are combustion and substitution processes. The exchange reactions proceed without changing the degrees of oxidation of substances. All other processes can be both ASP and BISO.

By changing the degree of oxidation, all chemical reactions can be divided into two types:

I. Reaction flowing without changing the degree of oxidation of elements included in the reactant substances. Such reactions relate to ion exchange reactions.

Na 2 CO 3 + H 2 SO 4 \u003d Na 2 SO 4 + CO 2 + H 2 O.

II. Reactions going with a change in the degree of oxidation of elements,

included in the reacting substances. Such reactions refer to oxidative reaction reactions.

5nano 2 + 2kmno 4 + 3H 2 SO 4 \u003d 5Nano 3 + 2mnso 4 + K 2 SO 4 + 3H 2 O.

Degree of oxidation(oxidation) - characteristics of the state of the atoms of elements in the composition of the molecule. It characterizes the uneven distribution of electrons between the atoms of the elements and corresponds to the charge, which would acquire an atom of the element, if all common electronic pairs of its chemical ties were shifted towards the more electronegative element. Depending on the relative electronegativity of the elements forming communication, the electron pair can be shifted to one of the atoms or is symmetrically located relative to the atomic cores. Therefore, the degree of oxidation of elements may have a negative, positive or zero value.

Elements whose atoms take electrons from other atoms have a negative degree of oxidation. Elements whose atoms give their electrons to other atoms, have a positive degree of oxidation. The zero degree of oxidation has atoms in molecules of simple substances, as well as if the substance is in atomic state.

The degree of oxidation is indicated +1, +2.

Charge ion 1+, 2+.

The degree of oxidation of the element in the connection is determined by the rules:

1. Sweep the oxidation of the element in simple substances equal to zero.

2. Extra elements in almost all of its compounds are manifested by a constant degree of oxidation. These elements include:

Himmes the degree of oxidation +1 (with the exception of metal hydrides).

Operates the degree of oxidation -2 (with the exception of fluorides).

3. Elements I, II and III groups of main subgroups Periodic system Elements of D.I. Inendeleev have a constant degree of oxidation equal to the number of the group.

Elements Na, Ba, Al: the degree of oxidation +1, + 2, + 3, respectively.

4. For elements having a variable degree of oxidation, there is a concept of the highest and lowest oxidation.

The highest degree of oxidation of the element is equal to the number of the group of the periodic system of elements of D.I. REMEELEEV, in which the element is located.

Elements N, Cl: the highest degree of oxidation + 5, + 7ctent.

The lower degree of oxidation of the element is equal to the number of the periodic system of elements of D.Iendeleev, in which the element is minus eight.

Elements N, Cl: lower degree of oxidation -3, -1, respectively.

5. In one-element ions, the degree of oxidation of the element is equal to the charge of the ion.

Fe 3+ - the degree of oxidation is +3; S 2- - the degree of oxidation is -2.

6. The system of degrees of oxidation of all atoms of elements in the molecule is zero.

KNO 3; (+1) + x + 3 · (-2) \u003d 0; X \u003d +5. The degree of oxidation of nitrogen is +5.

7. The soymma of the degrees of oxidation of all the atoms of elements in the ion is equal to the charge of the ion.

SO 4 2-; X + 4 · (-2) \u003d -2; X \u003d +6. The degree of sulfur oxidation is +6.

8. In compounds consisting of two elements, the element that is recorded on the right, always has a lower degree of oxidation.

Reactions in which the degree of oxidation of elements is changed to oxidative reducing reactions / OSR. These reactions consist of oxidation and recovery processes.

Oxidationthe process of electron recoil is called an element included in the atom, molecule or ion.

Al 0 - 3e \u003d Al 3+

H 2 - 2E \u003d 2H +

Fe 2+ - E \u003d Fe 3+

2CL - - 2E \u003d Cl 2

When oxidizing the degree of oxidation of the element rises. The substance (atom, molecule or ion), which includes an element, producing electrons, is called a reducing agent. Al, H 2, Fe 2+, Cl - - reducing agents. The reducing agent is oxidized.

Restorationthe process of connecting electrons is called an element included in the atom, molecule or ion.

CL 2 + 2E \u003d 2CL -

Fe 3+ + E \u003d Fe 2+

When restoring the degree of oxidation of the element decreases. The substance (atom, molecule or ion), which includes an element receiving electrons, is called an oxidizing agent. S, Fe 3+, Cl 2 - Oxidifiers. The oxidizer is restored.

The total number of electrons in the system during a chemical reaction does not change. The number of electrons given by the reducing agent is equal to the number of electrons connected by the oxidizing agent.

To compile the equation of the oxidation reaction (ORP) in solutions, an ion-electronic method (half-formation method) is used.

OSR can proceed in acidic, neutral or alkaline media. In the reaction equations, the possible participation of water molecules (HOH) and contained in the solution depending on the nature of the medium of excess ions H + or it is:

in an acidic environment - non and ions H +;

in the neutral medium - only non;

in an alkaline environment - non and ions it is.

In the preparation of the HSI equations, it is necessary to adhere to a specific sequence:

1. Laptop the reaction scheme.

2. Condiminate the elements that changed the degree of oxidation.

3. Laptop the scheme in a brief ion molecular form: strong electrolytes in the form of ions, weak electrolytes in the form of molecules.

4. Create equations of oxidation and recovery processes (half-resource equation). To do this, write elements that change the degree of oxidation in the form of real particles (ions, atoms, molecules) and equalize the number of each element in the left and right parts of the semi-reaction.

Note:

If the starting material contains less oxygen atoms than the products (r ro 4 3-), then the lack of oxygen is supplied by the medium.

If the starting material contains more oxygen atoms than products (SO 4 2- SO 2), then the exempted oxygen binds to the medium.

5. Eurade the left and right parts of the charges by the number of charges. To do this, add or subtract the required number of electrons.

6. Eating multipliers for semi-formations of oxidation and reduction so that the number of electrons during oxidation is equal to the number of electrons when recovered.

7.Simmage semicreecons of oxidation and recovery, taking into account the found factors.

8.Arted ion-molecular equation to write in molecular form.

9.Sclude oxygen check.

Three types of redox reactions distinguish:

a) intermolecular reactions in which the degree of oxidation changes in the elements that are part of various molecules.

2kmno 4 + 5Nano 2 + 3H 2 SO 4 2MNSO 4 + 5Nano 3 + K 2 SO 4 + 3H 2 O

b) intramolecular reactions in which the degree of oxidation changes in the elements that are part of the molecule.