Classification chemical reactions
Abstract on chemistry of a student of the 11th grade of secondary school No. 653 Alexey Nikolaev
The following can be selected as classification features:
1. The number and composition of the starting materials and reaction products.
2. Aggregate state of reactants and reaction products.
3. The number of phases in which the participants in the reaction are.
4. The nature of the carried particles.
5. The possibility of a reaction proceeding in the forward and reverse direction.
6. thermal effect.
7. The phenomenon of catalysis.
Classification according to the number and composition of the starting substances and reaction products.
Connection reactions.
In the reactions of a compound from several reacting substances of a relatively simple composition, one substance of a more complex composition is obtained:
A+B+C=D
As a rule, these reactions are accompanied by heat release, i.e. lead to the formation of more stable and less energy-rich compounds.
Inorganic chemistry.
The reactions of the combination of simple substances are always redox in nature. Connection reactions occurring between complex substances can occur both without a change in valence:
CaCO 3 + CO 2 + H 2 O \u003d Ca (HCO 3) 2,
and be classified as redox:
2FeCl 2 + Cl 2 = 2FeCl 3.
Organic chemistry.
AT organic chemistry such reactions are often referred to as addition reactions. They usually involve compounds containing a double or triple bond. Varieties of addition reactions: hydrogenation, hydration, hydrohalogenation, polymerization. Examples of these reactions:
T o
H 2 C \u003d CH 2 + H 2 → CH 3 - CH 3
ethylene ethane
T o
HC=CH + HCl → H 2 C=CHCl
acetylene vinyl chloride
T o
n CH 2 \u003d CH 2 → (-CH 2 -CH 2 -) n
Ethylene polyethylene
decomposition reactions.
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.
Inorganic chemistry.
Of the decomposition reactions that occur without changing the valence states, it should be noted the decomposition of crystalline hydrates, bases, acids and salts of oxygen-containing acids:
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t o |
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CuSO 4 5H 2 O |
CuSO 4 + 5H 2 O |
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t o |
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4HNO 3 |
2H 2 O + 4NO 2 O + O 2 O. |
2AgNO 3 \u003d 2Ag + 2NO 2 + O 2,
(NH 4) 2Cr 2 O 7 \u003d Cr 2 O 3 + N 2 + 4H 2 O.
Organic chemistry.
In organic chemistry, decomposition reactions include: dehydration, dehydrogenation, cracking, dehydrohalogenation, as well as depolymerization reactions, when the initial monomer is formed from the polymer. The corresponding reaction equations are:
T o
C 2 H 5 OH → C 2 H 4 + H 2 O
T o
C 6 H 14 → C 6 H 6 + 4H 2
hexane benzene
C 8 H 18 → C 4 H 10 + C 4 H 8
Octane Butane Butene
C 2 H5Br → C 2 H 4 + HBr
bromoethane ethylene
(-CH 2 - CH \u003d C - CH 2 -) n → n CH 2 \u003d CH - C \u003d CH 2
\CHz \CHz
natural rubber 2-methylbutadiene-1,3
substitution reactions.
In substitution reactions, usually a simple substance interacts with a complex one, forming another simple substance and another complex one:
A + BC = AB + C.
Inorganic chemistry.
These reactions in the vast majority belong to redox reactions:
2Al + Fe 2 O 3 \u003d 2Fe + Al 2 O 3
Zn + 2HCl = ZnCl 2 + H 2
2KBr + Cl 2 \u003d 2KCl + Br 2
2 KS lO 3 + l 2 \u003d 2KlO 3 + C l 2.
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:
CaCO 3 + SiO 2 \u003d CaSiO 3 + CO 2
Ca 3 (RO 4) 2 + ZSiO 2 = ZCaSiO 3 + P 2 O 5
Organic chemistry.
In organic chemistry, substitution reactions are understood more broadly, that is, not one atom, but a group of atoms can replace, or not an atom, but a group of atoms is replaced. A variety of substitution reactions include nitration and halogenation of saturated hydrocarbons, aromatic compounds and alcohols:
C 6 H 6 + Br 2 → C 6 H 5 Br + HBr
benzene bromobenzene
C 2 H 5 OH + HCl → C 2 H 5 Cl + H 2 O
Ethanol chloroethane
Exchange reactions.
Exchange reactionsReactions between two compounds that exchange their constituents are called:
AB + CD = AD + CB.
Inorganic chemistry
If redox processes occur during substitution reactions, then exchange reactions always occur without changing the valence state of atoms. This is the most common group of reactions between complex substances - oxides, bases, acids and salts:
ZnO + H 2 SO 4 \u003d ZnSO 4 + H 2 O
AgNO 3 + KBr = AgBr + KNO 3
CrCl 3 + ZNaOH = Cr(OH) 3 + ZNaCl.
A special case of these exchange reactions is neutralization reactions:
Hcl + KOH \u003d KCl + H 2 O.
Usually, 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-dissociation (for solutions) compound:
NaHCO 3 + HCl \u003d NaCl + H 2 O + CO 2
Ca (HCO 3) 2 + Ca (OH) 2 \u003d 2CaCO 3 ↓ + 2H 2 O
Organic chemistry
HCOOH + NaOH → HCOONa + H 2 O
formic acid sodium formate
hydrolysis reactions:
Na 2 CO3 + H 2 O
NaHCO3 + NaOH
sodium carbonate sodium bicarbonate
CO 3 + H 2 O
HCO 3 + OH
esterification reactions:
CH 3 COOH + C 2 H 5 OH
CH 3 COOC 2 H 5 + H 2 O
acetic ethanol ethyl acetate
Aggregate state of reactants and reaction products.
Gas reactions
|
t o |
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H 2 + Cl 2 |
2HCl. |
Reactions in solutions
NaOH (pp) + Hcl (p-p) \u003d NaCl (p-p) + H 2 O (l)
Reactions between solids
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t o |
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CaO (tv) + SiO 2 (tv) |
CaSiO 3 (TV) |
The number of phases in which the participants in the reaction are.
A phase is understood as a set of homogeneous parts of a system with the same physical and chemical properties and separated from each other by an interface.
Homogeneous (single-phase) reactions.
These include reactions occurring in the gas phase, and a number of reactions occurring in solutions.
Heterogeneous (multiphase) reactions.
These include reactions in which the reactants and products of the reaction are in different phases. For example:
gas-liquid phase reactions
CO 2 (g) + NaOH (p-p) = NaHCO 3 (p-p).
gas-solid-phase reactions
CO 2 (g) + CaO (tv) \u003d CaCO 3 (tv).
liquid-solid-phase reactions
Na 2 SO 4 (pp) + BaCl 3 (pp) \u003d BaSO 4 (tv) ↓ + 2NaCl (p-p).
liquid-gas-solid-phase reactions
Ca (HCO 3) 2 (pp) + H 2 SO 4 (pp) \u003d CO 2 (r) + H 2 O (l) + CaSO 4 (tv) ↓.
The nature of the carried particles.
protolytic reactions.
Protolytic reactions include chemical processes, the essence of which is the transfer of a proton from one reactant to another.
This classification is based on the protolytic theory of acids and bases, according to which any substance that donates a proton is considered an acid, and a substance capable of accepting a proton is considered a base, for example:
Protolytic reactions include neutralization and hydrolysis reactions.
Redox reactions.
All chemical reactions are divided into those in which the oxidation states do not change (for example, the exchange reaction) and those in which the oxidation states change. They are called redox reactions. They can be decomposition reactions, compounds, substitutions and other more complex reactions. For example:
Zn + 2 H + → Zn 2 + + H 2
FeS 2 + 8HNO 3 (conc ) \u003d Fe (NO 3) 3 + 5NO + 2H 2 SO 4 + 2H 2 O
The vast majority of chemical reactions are redox, they play an extremely important role.
ligand exchange reactions.
These include reactions during which the transfer of an electron pair occurs with the formation of a covalent bond by the donor-acceptor mechanism. For example:
Cu(NO 3) 2 + 4NH 3 = (NO 3) 2
Fe + 5CO =
Al(OH) 3 + NaOH =
A characteristic feature of ligand-exchange reactions is that the formation of new compounds, called complex ones, occurs without a change in the oxidation state.
The possibility of a reaction proceeding in the forward and reverse direction.
irreversible reactions.
irreversible call such chemical processes, whose products are not able to react with each other to form the starting substances. Examples of irreversible reactions are the decomposition of Bertolet salt when heated:
2KSlO 3 → 2KSl + ZO 2,
or oxidation of glucose with atmospheric oxygen:
C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O
reversible reactions.
reversible called such chemical processes, the products of which are able to react with each other under the same conditions in which they are obtained, with the formation of starting substances.
For reversible reactions, the equation is usually written as follows:
A+B
AB.
Two oppositely directed arrows indicate that under the same conditions, both forward and reverse reactions proceed simultaneously, for example:
CH 3 COOH + C 2 H 5 OH
CH 3 COOS 2 H 5 + H 2 O.
2SO2 +O2
2SO 3 + Q
Consequently, these reactions do not go to the end, because two reactions occur simultaneously - direct (between the starting materials) and reverse (decomposition of the reaction product).
Classification by thermal effect.
The amount of heat that is released or absorbed as a result of a reaction is called the thermal effect of this reaction. According to the thermal effect of the reaction, they are divided into:
exothermic.
Flow with heat
CH 4 + 2O 2 → CO 2 + 2H 2 O + Q
H 2 + Cl 2 → 2HC l + Q
Endothermic.
Flow with heat absorption
N 2 + O 2 → 2NO-Q
2Н 2 O → 2Н 2 + O 2 - Q
Classification taking into account the phenomenon of catalysis.
catalytic.
These include all processes involving catalysts.
Cat.
2SO2 + O2
2SO3
Non-catalytic.
These include any instantaneous reactions in solutions
BaCl 2 + H 2 SO 4 \u003d 2HCl + BaSO 4 ↓
Bibliography
Internet resources:
http://chem.km.ru - "World of Chemistry"
http:// chemi. org. ru – “Manual for applicants. Chemistry"
http://hemi. wallst. ru - "Alternative textbook in chemistry for grades 8-11"
"Guide to Chemistry. Applicants to universities "- E.T. Hovhannisyan, M. 1991
Big Encyclopedic Dictionary. Chemistry "- M. 1998.
AT inorganic chemistry Chemical reactions are classified according to different criteria.
1. By changing the oxidation state to redox, which go with a change in the oxidation state of the elements and acid-base, which proceed without changing the oxidation states.
2. By the nature of the process.
Decomposition reactions are chemical reactions in which simple molecules are formed from more complex ones.
Connection reactions chemical reactions are called, in which complex compounds are obtained from several simpler ones.
Substitution reactions are chemical reactions in which an atom or group of atoms in a molecule is replaced by another atom or group of atoms.
Exchange reactions called chemical reactions that occur without changing the oxidation state of elements and leading to the exchange constituent parts reagents.
3. If possible, proceed in the opposite direction to reversible and irreversible.
Some reactions, such as the combustion of ethanol, are practically irreversible, i.e. it is impossible to create conditions for it to flow in the opposite direction.
However, there are many reactions that, depending on the process conditions, can proceed both in the forward and reverse directions. Reactions that can proceed in both the forward and reverse directions are called reversible.
4. According to the type of bond rupture - homolytic(equal gap, each atom gets one electron) and heterolytic(unequal gap - one gets a pair of electrons).
5. According to the thermal effect, exothermic(heat generation) and endothermic(heat absorption).
Combination reactions will generally be exothermic reactions, while decomposition reactions will be endothermic. A rare exception is the endothermic reaction of nitrogen with oxygen N 2 + O 2 = 2NO - Q.
6. According to the state of aggregation of the phases.
homogeneous(the reaction takes place in one phase, without interfaces; reactions in gases or in solutions).
Heterogeneous(reactions taking place at the phase boundary).
7. By using a catalyst.
A catalyst is a substance that speeds up a chemical reaction but remains chemically unchanged.
catalytic practically do not go without the use of a catalyst and non-catalytic.
Classification of organic reactions
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Reaction type |
Radical |
Nucleophilic (N) |
Electrophilic (e) |
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Substitution (S) |
radical substitution (S R) |
Nucleophilic substitution (S N) |
Electrophilic substitution (S E) |
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Connection (A) |
radical connection (A R) |
Nucleophilic addition (A N) |
Electrophilic addition (A E) |
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Cleavage (E) (elimination) |
radical cleavage (E R) |
Nucleophilic cleavage (E N) |
Electrophilic elimination (E E) |
Heterolytic reactions are called electrophilic. organic compounds with electrophiles - particles that carry a whole or fractional positive charge. They are subdivided into electrophilic substitution and electrophilic addition reactions. For example,
H 2 C \u003d CH 2 + Br 2 BrCH 2 - CH 2 Br
Nucleophilic refers to heterolytic reactions of organic compounds with nucleophiles - particles that carry an integer or fractional negative charge. They are subdivided into nucleophilic substitution and nucleophilic addition reactions. For example,
CH 3 Br + NaOH CH 3 OH + NaBr
Radical (chain) reactions are called chemical reactions involving radicals, for example
>> Chemistry: Types of chemical reactions in organic chemistry
Reactions organic matter can be formally divided into four main types: substitutions, additions, eliminations (eliminations), and rearrangements (isomerizations). It is obvious that the whole variety of reactions of organic compounds cannot be reduced to the framework of the proposed classification (for example, combustion reactions). However, such a classification will help to establish analogies with the classifications of reactions that take place between inorganic substances already familiar to you from the course of inorganic chemistry.
As a rule, the main organic compound participating in the reaction is called the substrate, and the other component of the reaction is conditionally considered as a reagent.
Substitution reactions
Reactions that result in the replacement of one atom or group of atoms in the original molecule (substrate) with other atoms or groups of atoms are called substitution reactions.
Substitution reactions involve saturated and aromatic compounds, such as, for example, alkanes, cycloalkanes or arenes.
Let us give examples of such reactions.
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Slides captions:
Classification of chemical reactions
Chemical reactions - chemical processes, as a result of which some substances form others that differ from them in composition and (or) structure. In chemical reactions, a change in substances necessarily occurs, in which old bonds are broken and new bonds are formed between atoms. Signs of chemical reactions: A gas is released A precipitate will fall 3) A change in the color of substances occurs Heat, light is released or absorbed
Chemical reactions in inorganic chemistry
Chemical reactions in inorganic chemistry
Chemical reactions in inorganic chemistry 1. By changing oxidation states chemical elements: Redox reactions: Redox reactions are reactions that occur with a change in the oxidation states of elements. Intermolecular - this is a reaction that goes with a change in the oxidation state of atoms in different molecules. -2 +4 0 2H 2 S + H 2 SO 3 → 3S + 3H 2 O +2 -1 +2.5 -2 2Na 2 S 2 O 3 + H 2 O 2 → Na 2 S 4 O 6 + 2NaOH
Chemical reactions in inorganic chemistry 1. By changing the oxidation states of chemical elements that form substances: Redox reactions: 2. Intramolecular - this is a reaction that occurs with a change in the oxidation state of different atoms in one molecule. -3 +5 t 0 +3 (NH4) 2 Cr 2 O 7 → N 2 + Cr 2 O 3 + 4H 2 O Disproportionation is a reaction that occurs with a simultaneous increase and decrease in the oxidation state of atoms of the same element. +1 +5 -1 3NaClO → NaClO 3 + 2NaCl
2.1. Reactions that occur without changing the composition of substances In inorganic chemistry, such reactions include the processes of obtaining allotropic modifications of one chemical element, for example: C (graphite) C (diamond) 3O 2 (oxygen) 2O 3 (ozone) Sn (white tin) Sn ( gray tin) S (rhombic) S (plastic) P (red) P (white) Chemical reactions in inorganic chemistry 2. According to the number and composition of reactants:
Chemical reactions in inorganic chemistry 2. According to the number and composition of reactants: 2.2. Reactions that occur with a change in the composition of a substance Combination reactions are reactions in which one complex substance is formed from two or more substances. In inorganic chemistry, the whole variety of compound reactions can be considered using the example of the reaction for obtaining sulfuric acid from sulfur: a) obtaining sulfur oxide (IV): S + O 2 SO 2 - one complex substance is formed from two simple substances, b) obtaining sulfur oxide (VI ): 2 SO 2 + O 2 2SO 3 - one complex substance is formed from a simple and complex substance, c) obtaining sulfuric acid: SO 3 + H 2 O \u003d H 2 SO 4 - one complex substance is formed from two complex substances.
Chemical reactions in inorganic chemistry 2. According to the number and composition of the reacting substances: 2. Decomposition reactions are those reactions in which several new substances are formed from one complex substance. In inorganic chemistry, the whole variety of such reactions can be considered in the block of reactions for obtaining oxygen by laboratory methods: a) decomposition of mercury (II) oxide: 2HgO t 2Hg + O 2 - two simple ones are formed from one complex substance. b) decomposition of potassium nitrate: 2KNO 3 t 2KNO 2 + O 2 - one simple and one complex substance are formed from one complex substance. c) decomposition of potassium permanganate: 2 KMnO 4 → t K 2 MnO 4 + MnO 2 + O 2 - two complex and one simple are formed from one complex substance.
Chemical reactions in inorganic chemistry 2. According to the number and composition of reacting substances: 3. Substitution reactions are such reactions as a result of which atoms a simple substance replace the atoms of an element in a complex substance. In inorganic chemistry, an example of such processes can serve as a block of reactions that characterize the properties of metals: a) the interaction of alkali or alkaline earth metals with water: 2 Na + 2H 2 O = 2NaOH + H 2 Ca + 2H 2 O = Ca(OH) 2 + H 2 b) interaction of metals with acids in solution: Zn + 2HCl = ZnCl 2 + H 2 c ) interaction of metals with salts in solution: Fe + Cu SO 4 = FeSO 4 + Cu d) metallothermy: 2Al + Cr 2 O 3 t Al 2 O 3 + 2Cr
4. Exchange reactions are those reactions in which two complex substances exchange their constituents. These reactions characterize the properties of electrolytes and proceed in solutions according to the Berthollet rule, that is, only if a precipitate, gas, or a low-dissociating substance (for example, H 2 O) is formed as a result. In inorganic, this can be a block of reactions that characterize the properties of alkalis: a) a neutralization reaction that proceeds with the formation of salt and water: NaOH + HNO 3 \u003d NaNO 3 + H 2 O or in ionic form: OH - + H + \u003d H 2 O b ) the reaction between alkali and salt, which goes with the formation of gas: 2NH 4 Cl + Ca (OH) 2 \u003d CaCl 2 + 2NH 3 + 2 H 2 O c) the reaction between alkali and salt, which goes with the formation of a precipitate: Cu SO 4 + 2KOH \u003d Cu (OH) 2 + K 2 SO 4 Chemical reactions in inorganic chemistry 2. According to the number and composition of the reactants:
Chemical reactions in inorganic chemistry 3. According to the thermal effect: 3.1. Exothermic Reactions: Exothermic reactions are reactions that release energy into the environment. These include almost all compound reactions. Exothermic reactions that proceed with the release of light are referred to as combustion reactions, for example: 4P + 5O 2 \u003d 2P 2 O 5 + Q 3.2. Endothermic Reactions: Endothermic reactions are reactions that absorb energy into the environment. These include almost all decomposition reactions, for example: Calcining limestone: CaCO 3 t CaO + CO 2 - Q
Chemical reactions in inorganic chemistry 4. Process reversibility: 4.1. Irreversible reactions: Irreversible reactions proceed under given conditions in only one direction. Such reactions include all exchange reactions accompanied by the formation of a precipitate, gas or a low-dissociating substance (water) and all combustion reactions: S + O 2 SO 2; 4 P + 5O 2 2P 2 O 5; Cu SO 4 + 2KOH Cu(OH) 2 + K 2 SO 4 4.2. Reversible reactions: Reversible reactions under given conditions proceed simultaneously in two opposite directions. Most of these reactions are. For example: 2 SO 2 + O 2 2SO 3 N 2 + 3H 2 2NH 3
Catalysts are substances that take part in a chemical reaction and change its speed or direction, but at the end of the reaction remain unchanged qualitatively and quantitatively. 5.1. Non-catalytic reactions: Non-catalytic reactions are reactions that take place without the participation of a catalyst: 2HgO t 2Hg + O 2 2Al + 6HCl t 2AlCl 3 + 3H 2 5.2. Catalytic reactions: Catalytic reactions are reactions that take place with the participation of a catalyst: t ,MnO 2 2KClO 3 → 2KCl + 3O 2 P,t CO + NaOH H-CO-ONa Chemical reactions in inorganic chemistry 5 . Catalyst involvement
Chemical reactions in inorganic chemistry 6 . Presence of an interface between phases 6.1. Heterogeneous reactions: Heterogeneous reactions are reactions in which the reactants and reaction products are in different aggregate states (in different phases): FeO (t) + CO (g) Fe (t) + CO 2 (g) + Q 2 Al (t) + 3C u C l 2 (solution) \u003d 3C u (t) + 2AlCl 3 (solution) CaC 2 (t) + 2H 2 O (l) \u003d C 2 H 2 + Ca ( OH) 2 (solution) 6.2. Homogeneous reactions: Homogeneous reactions are reactions in which the reactants and reaction products are in the same state of aggregation(in one phase): 2C 2 H 6 (g) + 7O 2 (g) 4CO 2 (g) + 6H 2 O (g) 2 SO 2 (g) + O 2 (g) \u003d 2SO 3 (g) + Q H 2 (g) + F 2 (g) \u003d 2HF (g)
The classification of chemical reactions in inorganic and organic chemistry is carried out on the basis of various classifying features, details of which are given in the table below.
By changing the oxidation state of elements
The first sign of classification is by changing the degree of oxidation of the elements that form the reactants and products.
a) redox
b) without changing the oxidation state
redox called reactions accompanied by a change in the oxidation states of the chemical elements that make up the reagents. Redox in inorganic chemistry includes all substitution reactions and those decomposition and compound reactions in which at least one simple substance is involved. Reactions that proceed without changing the oxidation states of the elements that form the reactants and reaction products include all exchange reactions.
According to the number and composition of reagents and products
Chemical reactions are classified according to the nature of the process, i.e., according to the number and composition of reactants and products.
Connection reactions called chemical reactions, as a result of which complex molecules are obtained from several simpler ones, for example:
4Li + O 2 = 2Li 2 O
Decomposition reactions called chemical reactions, as a result of which simple molecules are obtained from more complex ones, for example:
CaCO 3 \u003d CaO + CO 2
Decomposition reactions can be viewed as processes inverse to compound.
substitution reactions chemical reactions are called, as a result of which an atom or group of atoms in a molecule of a substance is replaced by another atom or group of atoms, for example:
Fe + 2HCl \u003d FeCl 2 + H 2
Their distinguishing feature is the interaction of a simple substance with a complex one. Such reactions exist in organic chemistry.
However, the concept of "substitution" in organics is broader than in inorganic chemistry. If in the molecule of the original substance any atom or functional group are 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.
- exchange (including neutralization).
Exchange reactions call chemical reactions that occur without changing the oxidation states of the elements and lead to the exchange of the constituent parts of the reagents, for example:
AgNO 3 + KBr = AgBr + KNO 3
Run in the opposite direction if possible.
If possible, proceed in the opposite direction - reversible and irreversible.
reversible called chemical reactions occurring at a given temperature simultaneously in two opposite directions with commensurate speeds. When writing the equations of such reactions, the equal sign is replaced by oppositely directed arrows. The simplest example of a reversible reaction is the synthesis of ammonia by the interaction of nitrogen and hydrogen:
N 2 + 3H 2 ↔2NH 3
irreversible are reactions that proceed only in the forward direction, as a result of which products are formed that do not interact with each other. Irreversible include chemical reactions that result in the formation of poorly dissociated compounds, a large amount of energy is released, as well as those in which final products leave the reaction sphere in gaseous form or as a precipitate, for example:
HCl + NaOH = NaCl + H2O
2Ca + O 2 \u003d 2CaO
BaBr 2 + Na 2 SO 4 = BaSO 4 ↓ + 2NaBr
By thermal effect
exothermic are chemical reactions that release heat. Symbol changes in the enthalpy (heat content) ΔH, and the thermal effect of the reaction Q. For exothermic reactions, Q > 0, and ΔH< 0.
endothermic called chemical reactions that take place with the absorption of heat. For endothermic reactions Q< 0, а ΔH > 0.
Coupling reactions will generally be exothermic reactions, and decomposition reactions will be endothermic. A rare exception is the reaction of nitrogen with oxygen - endothermic:
N2 + O2 → 2NO - Q
By phase
homogeneous called reactions occurring in a homogeneous medium (homogeneous substances, in one phase, for example, g-g, reactions in solutions).
heterogeneous called reactions occurring in an inhomogeneous medium, on the contact surface of the reacting substances that are in different phases, for example, solid and gaseous, liquid and gaseous, in two immiscible liquids.
By using a catalyst
A catalyst is a substance that speeds up a chemical reaction.
catalytic reactions proceed only in the presence of a catalyst (including enzymatic ones).
Non-catalytic reactions run in the absence of a catalyst.
By type of rupture
By type of break chemical bond in the original molecule, homolytic and heterolytic reactions are distinguished.
homolytic called reactions in which, as a result of breaking bonds, particles are formed that have an unpaired electron - free radicals.
Heterolytic called reactions that proceed through the formation of ionic particles - cations and anions.
- homolytic (equal gap, each atom receives 1 electron)
- heterolytic (unequal gap - one gets a pair of electrons)
Radical(chain) chemical reactions involving radicals are called, for example:
CH 4 + Cl 2 hv → CH 3 Cl + HCl
Ionic called chemical reactions that take place with the participation of ions, for example:
KCl + AgNO 3 \u003d KNO 3 + AgCl ↓
Electrophilic refers to heterolytic reactions of organic compounds with electrophiles - particles that carry a whole or fractional positive charge. They are divided into reactions of electrophilic substitution and electrophilic addition, for example:
C 6 H 6 + Cl 2 FeCl3 → C 6 H 5 Cl + HCl
H 2 C \u003d CH 2 + Br 2 → BrCH 2 -CH 2 Br
Nucleophilic refers to heterolytic reactions of organic compounds with nucleophiles - particles that carry an integer or fractional negative charge. They are subdivided into nucleophilic substitution and nucleophilic addition reactions, for example:
CH 3 Br + NaOH → CH 3 OH + NaBr
CH 3 C (O) H + C 2 H 5 OH → CH 3 CH (OC 2 H 5) 2 + H 2 O
Classification of organic reactions
Classification organic reactions is shown in the table:
