Classification of chemical reactions in inorganic and organic chemistry.
Lecture: Classification of chemical reactions in inorganic and organic chemistry
Types of chemical reactions in inorganic chemistry
A) Classification according to the amount of initial substances:
Decomposition – as a result of this reaction, from one existing complex substance, two or more simple and also complex substances are formed.
Example: 2H 2 O 2 → 2H 2 O + O 2Compound - this is a reaction in which two or more simple, as well as complex substances, form one, but more complex one.
Example: 4Al+3O 2 → 2Al 2 O 3
Substitution - this is a certain chemical reaction that takes place between some simple and also complex substances. Atoms of a simple substance, in this reaction, are replaced by atoms of one of the elements found in the complex substance.Example: 2КI + Cl2 → 2КCl + I 2
Exchange - This is a reaction in which two substances of complex structure exchange their parts.Example: HCl + KNO 2 → KCl + HNO 2
B) Classification by thermal effect:
Exothermic reactions - These are certain chemical reactions in which heat is released.Examples:
S + O 2 → SO 2 + Q
2C 2 H 6 + 7O 2 → 4CO 2 +6H 2 O + Q
Endothermic reactions
- These are certain chemical reactions in which heat is absorbed. As a rule, these are decomposition reactions.
Examples:
CaCO 3 → CaO + CO 2 – Q
2KClO 3 → 2KCl + 3O 2 – Q
The heat that is released or absorbed as a result of a chemical reaction is called thermal effect.
Chemical equations that indicate the thermal effect of a reaction are called thermochemical.
B) Classification by reversibility:
Reversible reactions - these are reactions that occur under the same conditions in mutually opposite directions.Example: 3H 2 + N 2 ⇌ 2NH 3
Irreversible reactions - these are reactions that proceed in only one direction, and also end with the complete consumption of all starting substances. In these reactions, release there is gas, sediment, water.Example: 2KClO 3 → 2KCl + 3O 2
D) Classification by change in oxidation state:
Redox reactions – during these reactions, a change in the oxidation state occurs.Example: Cu + 4HNO 3 → Cu(NO 3) 2 + 2NO 2 + 2H 2 O.
Not redox – reactions without changing the oxidation state.Example: HNO 3 + KOH → KNO 3 + H 2 O.
D) Classification by phase:
Homogeneous reactions – reactions occurring in one phase, when the starting substances and reaction products have the same state of aggregation.Example: H 2 (gas) + Cl 2 (gas) → 2HCL
Heterogeneous reactions – reactions occurring at the interface, in which the reaction products and starting substances have different states of aggregation.Example: CuO+ H 2 → Cu+H 2 O
Classification by catalyst use:
A catalyst is a substance that speeds up a reaction. A catalytic reaction occurs in the presence of a catalyst, a non-catalytic reaction occurs without a catalyst.
Example: 2H 2 0 2 MnO2 →
2H 2 O + O 2 catalyst MnO 2
The interaction of alkali with acid occurs without a catalyst.
Example: KOH + HCl →
KCl + H 2 O
Inhibitors are substances that slow down a reaction.
Catalysts and inhibitors themselves are not consumed during the reaction.
Types of chemical reactions in organic chemistry
Substitution is a reaction during which one atom/group of atoms in the original molecule is replaced by other atoms/groups of atoms.
Example: CH 4 + Cl 2 → CH 3 Cl + HCl
Accession - These are reactions in which several molecules of a substance combine into one. Addition reactions include:
- Hydrogenation is a reaction during which hydrogen is added to a multiple bond.
Example: CH 3 -CH = CH 2 (propene) + H 2 → CH 3 -CH 2 -CH 3 (propane)
Hydrohalogenation– reaction that adds hydrogen halide.
Example: CH 2 = CH 2 (ethene) + HCl → CH 3 -CH 2 -Cl (chloroethane)
Alkynes react with hydrogen halides (hydrogen chloride, hydrogen bromide) in the same way as alkenes. Addition in a chemical reaction takes place in 2 stages, and is determined by Markovnikov’s rule:
When protic acids and water add to unsymmetrical alkenes and alkynes, a hydrogen atom is added to the most hydrogenated carbon atom.
The mechanism of this chemical reaction. Formed in the 1st, fast stage, the p-complex in the 2nd slow stage gradually turns into an s-complex - a carbocation. In the 3rd stage, stabilization of the carbocation occurs - that is, interaction with the bromine anion:
I1, I2 are carbocations. P1, P2 - bromides.
Halogenation - a reaction in which a halogen is added. Halogenation also refers to all processes as a result of which halogen atoms are introduced into organic compounds. This concept is used in a “broad sense”. In accordance with this concept, the following chemical reactions based on halogenation are distinguished: fluorination, chlorination, bromination, iodination.
Halogen-containing organic derivatives are considered the most important compounds that are used both in organic synthesis and as target products. Halogen derivatives of hydrocarbons are considered starting products in a large number of nucleophilic substitution reactions. As for the practical use of halogen-containing compounds, they are used in the form of solvents, for example chlorine-containing compounds, refrigerants - chlorofluoro derivatives, freons, pesticides, pharmaceuticals, plasticizers, monomers for the production of plastics.
Hydration– reactions of addition of a water molecule through a multiple bond.
Polymerization is a special type of reaction in which molecules of a substance with a relatively low molecular weight attach to each other, subsequently forming molecules of a substance with a high molecular weight.
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Classification of chemical reactions.
Chemical reactions are classified according to changes in the number and composition of starting substances and reaction products into the following types:
connection reactions- several substances are combined into one product;
decomposition reactions- several products are formed from one starting substance;
substitution reactions- a simple substance replaces part of the atoms of a complex substance;
exchange reactions- complex substances exchange their constituent parts.
According to the thermal effect, chemical reactions can be divided into exothermic- flowing with the release of heat and endothermic- proceeding with the absorption of heat.
Taking into account the phenomenon of catalysis, reactions can be catalytic- using catalysts and non-catalytic- without the use of catalysts.
Based on the change in oxidation state, reactions are divided into redox– in them there is a change in the oxidation states of atoms, and the reaction without changing oxidation states atoms.
Based on the presence of a phase interface, reactions are divided into homogeneous and heterogeneous. Homogeneous processes occur in one phase, heterogeneous processes occur at the phase interface.
Based on reversibility, reactions are divided into reversible And irreversible. Irreversible reactions proceed to completion until the substances react completely; reversible - until chemical equilibrium is achieved, which is characterized by equal rates of forward and reverse reactions and the presence in the reaction mixture of both starting materials and reaction products.
Chemical equilibrium is dynamic, and it can be shifted in one direction or another by changing reaction conditions (concentrations of substances, temperature, pressure). The direction of the equilibrium shift can be predicted using Le Chatelier's principle: if a system in equilibrium is influenced by external factors, then the equilibrium in the system shifts towards the reaction that weakens this influence.
Chemical reactions occur at certain rates. The branch of chemistry that studies the influence of various factors on the rate of chemical reactions, as well as the mechanisms of chemical transformations, is called chemical kinetics.
Factors influencing the rate of a chemical reaction: temperature, pressure, concentration of substances, presence of a catalyst.
The effect of temperature on the rate of reactions is determined by Van't Hoff's rule: in the temperature range from 0 o C to 100 o C, with every 10 degree increase in temperature, the rate of a chemical reaction increases by 2-4 times.
Catalysis- selective acceleration of one of the directions of a chemical reaction under the influence of a catalyst. Catalysts take part in intermediate processes, but are restored at the end of the reaction. The phenomenon of catalysis is widespread in nature (most processes occurring in living organisms are catalytic) and is widely used in technology (in oil refining and petrochemistry, in the production of sulfuric acid, ammonia, nitric acid, etc.). The majority of all industrial reactions are catalytic.
There is negative catalysis or inhibition. Inhibitors– substances that slow down a chemical reaction (for example, corrosion inhibitors).
A special group is formed by autocatalytic reactions. In them, one of the reaction products serves as a catalyst for the conversion of the starting substances.
Natural catalysts are called enzymes, enzymes accelerate biochemical processes inside the body. The starting materials for the synthesis of enzymes are coenzymes. The body cannot synthesize a number of coenzymes from food and must receive them in finished form. This is, for example, vitamins.
The variety of chemical reactions, the number of which cannot be counted, cannot be covered by a single universal classification, therefore they are divided according to certain common characteristics. Any of these characteristics can include reactions between both inorganic and organic substances.
Firstly, these are reactions without changing the composition of the substance and reactions with a change in composition.
Reactions that occur without changing the composition of substances:
AlCl3,t
CH3-CH2-CH2-CH3 > CH3-CH-CH3
Reactions that occur with a change in the composition of substances:
6 CO2 + 6 H2O = C6H12O6 + 6 O2
In organic chemistry, this type of reaction includes isomerization reactions. Thus, isomerization of alkanes is carried out to obtain gasoline with a high octane number.
For chemical processes occurring between inorganic reagents, the following classifications are most often used:
1. The number and composition of starting substances and reaction products.
2. Physical state of the reagents and reaction products.
3. The number of phases in which the reaction participants are located.
4. Nature of transferred particles.
5. Possibility of the reaction occurring in forward and reverse directions.
6. Thermal effect sign
Different classification methods are often combined with each other (Fig. 1).
Figure 1 - Sign of classification of chemical reactions
Let's take a closer look at each type of chemical reaction.
1. Classification according to the number and composition of reagents and final substances (Table 1).
Table 1 - Types of chemical reactions and their mechanisms
1. Compound reactions. D.I. Mendeleev defined a compound as a reaction “in which one of two substances occurs. So, when a compound reacts from several reacting substances of relatively simple composition, one substance of a more complex composition is obtained
Compound reactions include combustion processes of simple substances (sulfur, phosphorus, carbon) in air. For example, carbon burns in air C + O 2 = CO 2 (of course, this reaction occurs gradually, first carbon monoxide CO is formed). As a rule, these reactions are accompanied by the release of heat, i.e. lead to the formation of more stable and less energy-rich compounds - they are exothermic.
Reactions of compounds of simple substances are always redox in nature. Compound reactions occurring between complex substances can occur without a change in valence
CaCO3 + CO2 + H2O = Ca (HCO3)2
so belong to the number of redox
2FeCl2 + Cl2 = 2FeCl3.
2. Decomposition reactions. Chemical decomposition reactions, according to Mendeleev, “are cases inverse to combination, that is, those in which one substance produces two, or, in general, a given number of substances produces a greater number of them.
Decomposition reactions lead to the formation of several compounds from one complex substance
A = B + C + D
The decomposition products of a complex substance can be both simple and complex substances. An example of a decomposition reaction is the chemical reaction of chalk decomposition (or limestone under the influence of temperature): CaCO 3 = CaO + CO 2. Heat is generally required for the decomposition reaction to occur. Such processes are endothermic, i.e. proceed with the absorption of heat. Of the decomposition reactions that occur without changing the valence states, noteworthy is the decomposition of crystalline hydrates, bases, acids and salts of oxygen-containing acids
CuSO4 5H2O = CuSO4 + 5H2O,
Cu(OH)2 = CuO + H2O,
H2SiO3 = SiO2 + H2O.
Redox decomposition reactions include the decomposition of oxides, acids and salts formed by elements in higher oxidation states
2SO3 = 2SO2 + O2,
4HNO3 = 2H2O + 4NO2O + O2O,
2AgNO3 = 2Ag + 2NO2 + O2,
(NH4) 2Cr2O7 = Cr2O3 + N2 + 4H2O.
Redox decomposition reactions are especially characteristic for salts of nitric acid.
Decomposition reactions in organic chemistry, in contrast to decomposition reactions in inorganic chemistry, have their own specifics. They can be considered as processes inverse to addition, since they most often result in the formation of multiple bonds or cycles.
Decomposition reactions in organic chemistry are called cracking
С18H38 = С9H18 + С9H20
or dehydrogenation C4H10 = C4H6 + 2H2.
In the other two types of reactions, the number of reactants is equal to the number of products.
3. Substitution reactions. Their distinguishing feature is the interaction of a simple substance with a complex one. Such reactions also exist in organic chemistry. However, the concept of “substitution” in organic chemistry is broader than in inorganic chemistry. If in the molecule of the original substance any atom or functional group is replaced by another atom or group, these are also substitution reactions, although from the point of view of inorganic chemistry the process looks like an exchange reaction.
In substitution reactions, a simple substance usually reacts with a complex substance, forming another simple substance and another complex A + BC = AB + C
For example, by dipping a steel nail into a solution of copper sulfate, we obtain iron sulfate (iron displaced copper from its salt) Fe + CuSO 4 = FeSO 4 + Cu.
These reactions overwhelmingly belong to redox reactions.
2Al + Fe2O3 = 2Fe + Al2O3,
Zn + 2HCl = ZnСl2 + H2,
2KBr + Cl2 = 2KCl + Br2,
2КlO3 + l2 = 2KlO3 + Сl2.
Examples of substitution reactions that are not accompanied by a change in the valence states of atoms are extremely few.
It should be noted the reaction of silicon dioxide with salts of oxygen-containing acids, which correspond to gaseous or volatile anhydrides
CaCO3+ SiO2 = CaSiO3 + CO2,
Ca3(PO4)2 + 3SiO2 = 3CaSiO3 + P2O5.
Sometimes these reactions are considered as exchange reactions
CH4 + Cl2 = CH3Cl + HCl.
4. Exchange reactions (including neutralization). Exchange reactions are reactions between two compounds that exchange their constituents with each other.
AB + CD = AD + CB
A large number of them occur in aqueous solutions. An example of a chemical exchange reaction is the neutralization of an acid with an alkali
NaOH+HCl=NaCl+H 2 O.
Here, in the reactants (substances on the left), a hydrogen ion from the compound HCl is exchanged with a sodium ion from the compound NaOH, resulting in the formation of a solution of table salt in water.
If redox processes occur during substitution reactions, then exchange reactions always occur without changing the valence state of the atoms. This is the most common group of reactions between complex substances - oxides, bases, acids and salts
ZnO + Н2SO4 = ZnSO4 + Н2О,
AgNO3 + KBr = AgBr + KNO3,
CrCl3 + 3NaOH = Cr(OH)3 + 3NaCl.
A special case of these exchange reactions is the neutralization reaction
HCl + KOH = KCl + H2O.
Typically, these reactions obey the laws of chemical equilibrium and proceed in the direction where at least one of the substances is removed from the reaction sphere in the form of a gaseous, volatile substance, precipitate or low-dissociating (for solutions) compound
NaHCO3 + HCl = NaCl + H2O + CO2^,
Ca(HCO3)2 + Ca(OH)2 = 2CaCO3v + 2H2O,
CH3COONa + H3PO4 = CH3COON + NaH2PO4.
However, many reactions do not fit into the given simple scheme. For example, the chemical reaction between potassium permanganate (potassium permanganate) and sodium iodide cannot be classified as one of these types. Such reactions are usually called redox reactions, for example
2KMnO 4 +10NaI+ 8H2SO4=2MnSO4+K2SO4+5Na2SO4+5I2+8H2O.
Redox reactions in inorganic chemistry include all substitution reactions and those decomposition and combination reactions in which at least one simple substance is involved. In a more generalized version (including organic chemistry), all reactions involving simple substances. And, conversely, reactions that occur without changing the oxidation states of the elements that form the reactants and reaction products include all exchange reactions.
2. Classification of reactions according to phase characteristics
Depending on the state of aggregation of the reacting substances, the following reactions are distinguished:
1. Gas reactions:
2. Reactions in solutions:
NaOH(solution) + HCl(p-p) = NaCl(p-p) + H2O(l).
3. Reactions between solids:
CaO(s) + SiO2(s) = CaSiO3(s).
A chemical reaction is a process of transformation of substances during which a change in their structure or composition is observed. As a result of this process, the starting substances, or reagents, are converted into final products. Today, a very clear classification of chemical reactions has been formed.
Describe reactions using equations. Signs of chemical reactions
There are several classifications, each of which takes into account one or more characteristics. For example, chemical reactions can be divided by paying attention to:
- quantity and composition of reagents and final products;
- state of aggregation of initial and final substances (gas, liquid, solid form);
- number of phases;
- the nature of the particles that are transferred during the reaction (ion, electron);
- thermal effect;
- the possibility of the reaction occurring in the opposite direction.
It is worth noting that chemical reactions are usually written using formulas and equations. In this case, the left side of the equation describes the composition of the reagents and the nature of their interaction, and on the right side you can see the final products. Another very important point is that the number of atoms of each element on the right and left sides must be equal. This is the only way it is observed
As already mentioned, there are many classifications. The most commonly used ones will be discussed here.
Classification of chemical reactions by composition, quantity of initial and final products
They contain several substances that combine to form a more complex substance. In most cases, this reaction is accompanied by the release of heat.
The starting reagent is a complex compound, which during the decomposition process forms several simpler substances. Such reactions can be either redox or occur without a change in valence.
Substitution reactions are the interaction between a complex and a simple substance. In the process, the replacement of any atom of a complex substance occurs. The reaction can be shown schematically as follows:
A + BC = AB + C
Exchange reactions are a process during which two starting reagents exchange their constituent parts with each other. For example:
AB + SD = AD + SV
Transfer reactions are characterized by the transfer of an atom or group of atoms from one substance to another.
Classification of chemical reactions: reversible and irreversible processes
Another important characteristic of reactions is the possibility of a reverse process.
So, reversible reactions are those reactions whose products can interact with each other, forming the same starting substances. As a rule, this feature must be displayed in the equation. In this case, two oppositely directed arrows are placed between the left and right sides of the equation.
In an irreversible chemical reaction, its products are not able to react with each other - at least under normal conditions.
Classification of chemical reactions by thermal effect
Thermochemical reactions are divided into two main groups:
- exothermic processes, during which the release of heat (energy) is observed;
- endothermic processes that require the absorption of energy from the outside.
Classification of chemical reactions by the number of phases and phase characteristics
As already mentioned, substances are also of great importance for the complete characterization of a chemical reaction. Based on these characteristics, it is customary to distinguish:
- gas reactions;
- reactions in solutions;
- chemical processes between
But the initial and final products do not always belong to any one state of aggregation. Therefore, reactions are classified based on the number of phases:
- single-phase or homogeneous reactions are processes whose products are in the same state (in most cases, such a reaction occurs either in the gas phase or in solution);
- (multiphase) - reactants and final products can be in different states of aggregation.
DEFINITION
Chemical reaction are called transformations of substances in which a change in their composition and (or) structure occurs.
Most often, chemical reactions are understood as the process of converting starting substances (reagents) into final substances (products).
Chemical reactions are written using chemical equations containing the formulas of the starting substances and reaction products. According to the law of conservation of mass, the number of atoms of each element on the left and right sides of a chemical equation is the same. Typically, the formulas of the starting substances are written on the left side of the equation, and the formulas of the products on the right. The equality of the number of atoms of each element on the left and right sides of the equation is achieved by placing integer stoichiometric coefficients in front of the formulas of substances.
Chemical equations may contain additional information about the characteristics of the reaction: temperature, pressure, radiation, etc., which is indicated by the corresponding symbol above (or “below”) the equal sign.
All chemical reactions can be grouped into several classes, which have certain characteristics.
Classification of chemical reactions according to the number and composition of starting and resulting substances
According to this classification, chemical reactions are divided into reactions of connection, decomposition, substitution, and exchange.
As a result compound reactions from two or more (complex or simple) substances one new substance is formed. In general, the equation for such a chemical reaction will look like this:
For example:
CaCO 3 + CO 2 + H 2 O = Ca(HCO 3) 2
SO 3 + H 2 O = H 2 SO 4
2Mg + O 2 = 2MgO.
2FeCl 2 + Cl 2 = 2FeCl 3
The reactions of the compound are in most cases exothermic, i.e. proceed with the release of heat. If simple substances are involved in the reaction, then such reactions are most often redox reactions (ORR), i.e. occur with changes in the oxidation states of elements. It is impossible to say unambiguously whether the reaction of a compound between complex substances will be classified as ORR.
Reactions that result in the formation of several other new substances (complex or simple) from one complex substance are classified as decomposition reactions. In general, the equation for the chemical reaction of decomposition will look like this:
For example:
CaCO 3 CaO + CO 2 (1)
2H 2 O = 2H 2 + O 2 (2)
CuSO 4 × 5H 2 O = CuSO 4 + 5H 2 O (3)
Cu(OH) 2 = CuO + H 2 O (4)
H 2 SiO 3 = SiO 2 + H 2 O (5)
2SO 3 =2SO 2 + O 2 (6)
(NH 4) 2 Cr 2 O 7 = Cr 2 O 3 + N 2 +4H 2 O (7)
Most decomposition reactions occur when heated (1,4,5). Possible decomposition under the influence of electric current (2). The decomposition of crystalline hydrates, acids, bases and salts of oxygen-containing acids (1, 3, 4, 5, 7) occurs without changing the oxidation states of the elements, i.e. these reactions are not related to ODD. ORR decomposition reactions include the decomposition of oxides, acids and salts formed by elements in higher oxidation states (6).
Decomposition reactions are also found in organic chemistry, but under other names - cracking (8), dehydrogenation (9):
C 18 H 38 = C 9 H 18 + C 9 H 20 (8)
C 4 H 10 = C 4 H 6 + 2H 2 (9)
At substitution reactions a simple substance interacts with a complex substance, forming a new simple and a new complex substance. In general, the equation for a chemical substitution reaction will look like this:
For example:
2Al + Fe 2 O 3 = 2Fe + Al 2 O 3 (1)
Zn + 2HCl = ZnСl 2 + H 2 (2)
2KBr + Cl 2 = 2KCl + Br 2 (3)
2КlO 3 + l 2 = 2KlO 3 + Сl 2 (4)
CaCO 3 + SiO 2 = CaSiO 3 + CO 2 (5)
Ca 3 (PO 4) 2 + 3SiO 2 = 3СаSiO 3 + P 2 O 5 (6)
CH 4 + Cl 2 = CH 3 Cl + HCl (7)
Most substitution reactions are redox (1 – 4, 7). Examples of decomposition reactions in which no change in oxidation states occurs are few (5, 6).
Exchange reactions are reactions that occur between complex substances in which they exchange their constituent parts. Typically this term is used for reactions involving ions in aqueous solution. In general, the equation for a chemical exchange reaction will look like this:
AB + CD = AD + CB
For example:
CuO + 2HCl = CuCl 2 + H 2 O (1)
NaOH + HCl = NaCl + H 2 O (2)
NaHCO 3 + HCl = NaCl + H 2 O + CO 2 (3)
AgNO 3 + KBr = AgBr ↓ + KNO 3 (4)
CrCl 3 + ZNaON = Cr(OH) 3 ↓+ ZNaCl (5)
Exchange reactions are not redox. A special case of these exchange reactions is the neutralization reaction (the reaction of acids with alkalis) (2). Exchange reactions proceed in the direction where at least one of the substances is removed from the reaction sphere in the form of a gaseous substance (3), a precipitate (4, 5) or a poorly dissociating compound, most often water (1, 2).
Classification of chemical reactions according to changes in oxidation states
Depending on the change in the oxidation states of the elements that make up the reagents and reaction products, all chemical reactions are divided into redox reactions (1, 2) and those occurring without changing the oxidation state (3, 4).
2Mg + CO 2 = 2MgO + C (1)
Mg 0 – 2e = Mg 2+ (reducing agent)
C 4+ + 4e = C 0 (oxidizing agent)
FeS 2 + 8HNO 3 (conc) = Fe(NO 3) 3 + 5NO + 2H 2 SO 4 + 2H 2 O (2)
Fe 2+ -e = Fe 3+ (reducing agent)
N 5+ +3e = N 2+ (oxidizing agent)
AgNO 3 +HCl = AgCl ↓ + HNO 3 (3)
Ca(OH) 2 + H 2 SO 4 = CaSO 4 ↓ + H 2 O (4)
Classification of chemical reactions by thermal effect
Depending on whether heat (energy) is released or absorbed during the reaction, all chemical reactions are conventionally divided into exothermic (1, 2) and endothermic (3), respectively. The amount of heat (energy) released or absorbed during a reaction is called the thermal effect of the reaction. If the equation indicates the amount of heat released or absorbed, then such equations are called thermochemical.
N 2 + 3H 2 = 2NH 3 +46.2 kJ (1)
2Mg + O 2 = 2MgO + 602.5 kJ (2)
N 2 + O 2 = 2NO – 90.4 kJ (3)
Classification of chemical reactions according to the direction of the reaction
Based on the direction of the reaction, a distinction is made between reversible (chemical processes whose products are capable of reacting with each other under the same conditions in which they were obtained to form the starting substances) and irreversible (chemical processes whose products are not able to react with each other to form the starting substances). ).
For reversible reactions, the equation in general form is usually written as follows:
A + B ↔ AB
For example:
CH 3 COOH + C 2 H 5 OH ↔ H 3 COOC 2 H 5 + H 2 O
Examples of irreversible reactions include the following reactions:
2КlО 3 → 2Кl + ЗО 2
C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O
Evidence of the irreversibility of a reaction can be the release of a gaseous substance, a precipitate, or a poorly dissociating compound, most often water, as reaction products.
Classification of chemical reactions according to the presence of a catalyst
From this point of view, catalytic and non-catalytic reactions are distinguished.
A catalyst is a substance that speeds up the progress of a chemical reaction. Reactions that occur with the participation of catalysts are called catalytic. Some reactions cannot take place at all without the presence of a catalyst:
2H 2 O 2 = 2H 2 O + O 2 (MnO 2 catalyst)
Often one of the reaction products serves as a catalyst that accelerates this reaction (autocatalytic reactions):
MeO+ 2HF = MeF 2 + H 2 O, where Me is a metal.
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