Themes USE codifier: Classification chemical reactions in organic and not organic chemistry.
chemical reactions - this is a kind of interaction of particles, when from one chemical substances others are obtained, differing from them in properties and structure. Substances that enter in reaction - reagents. Substances that formed during a chemical reaction products.
During a chemical reaction, chemical bonds are broken and new ones are formed.
During chemical reactions, the atoms involved in the reaction do not change. Only the order of connection of atoms in molecules changes. Thus, the number of atoms of the same substance does not change during a chemical reaction.
Chemical reactions are classified according to different criteria. Consider the main types of classification of chemical reactions.
Classification according to the number and composition of reactants
According to the composition and number of reacting substances, reactions proceeding without a change in the composition of substances are divided, and reactions occurring with a change in the composition of substances:
1. Reactions proceeding without changing the composition of substances (A → B)
For such reactions in inorganic chemistry allotropic transitions of simple substances from one modification to another can be attributed:
S rhombic → S monoclinic.
AT organic chemistry such reactions are isomerization reactions , when another isomer is obtained from one isomer under the action of a catalyst and external factors (as a rule, a structural isomer).
for example, isomerization of butane to 2-methylpropane (isobutane):
CH 3 -CH 2 -CH 2 -CH 3 → CH 3 -CH (CH 3) -CH 3.
2. Reactions occurring with a change in composition
- Coupling reactions (A + B + ... →D)- these are reactions in which one new complex substance is formed from two or more substances. AT inorganic chemistry The compound reaction includes combustion reactions of simple substances, the interaction of basic oxides with acid ones, etc. In organic chemistry such reactions are called reactions accession . Addition reactions — these are reactions in which another molecule is attached to the organic molecule in question. Addition reactions include reactions hydrogenation(interaction with hydrogen), hydration(water connection), hydrohalogenation(addition of hydrogen halide), polymerization(attachment of molecules to each other with the formation of a long chain), etc.
for example, hydration:
CH 2 \u003d CH 2 + H 2 O → CH 3 -CH 2 -OH
- Decomposition reactions (A → B+C+…) These are reactions in the course of which several less complex or simple substances are formed from one complex molecule. In this case, both simple and complex substances can be formed.
for example, when decomposing hydrogen peroxide:
2H2O2→ 2H 2 O + O 2 .
In organic chemistry separate the actual decomposition reactions and the cleavage reactions . Cleavage (elimination) reactions — these are reactions in which atoms or atomic groups are detached from the original molecule while maintaining its carbon skeleton.
for example, the reaction of hydrogen abstraction (dehydrogenation) from propane:
C 3 H 8 → C 3 H 6 + H 2
As a rule, in the name of such reactions there is a prefix "de". Decomposition reactions in organic chemistry occur, as a rule, with a break in the carbon chain.
for example, reaction butane cracking(cleavage into simpler molecules when heated or under the action of a catalyst):
C 4 H 10 → C 2 H 4 + C 2 H 6
- Substitution reactions - these are reactions in which atoms or groups of atoms of one substance are replaced by atoms or groups of atoms of another substance. In inorganic chemistry These reactions proceed according to the scheme:
AB+C=AC+B.
for example, more active halogens displace less active compounds. Interaction potassium iodide with chlorine:
2KI + Cl 2 → 2KCl + I 2 .
Both individual atoms and molecules can be replaced.
for example, when fused less volatile oxides push out more volatile from salts. Yes, non-volatile silicon oxide displaces carbon monoxide from sodium carbonate when melting:
Na 2 CO 3 + SiO 2 → Na 2 SiO 3 + CO 2
AT organic chemistry substitution reactions are reactions in which part of an organic molecule replaced to other particles. In this case, the substituted particle, as a rule, combines with a part of the substituent molecule.
for example, reaction methane chlorination:
CH 4 + Cl 2 → CH 3 Cl + HCl
In terms of the number of particles and the composition of the interaction products, this reaction is more similar to an exchange reaction. However, by mechanism such a reaction is a substitution reaction.
- Exchange reactions are reactions in which two complex substances exchange their components:
AB+CD=AC+BD
The exchange reactions are ion exchange reactions flowing in solutions; reactions illustrating the acid-base properties of substances and others.
Example exchange reactions in inorganic chemistry - neutralization of hydrochloric acid alkali:
NaOH + HCl \u003d NaCl + H 2 O
Example exchange reactions in organic chemistry — alkaline hydrolysis of chloroethane:
CH 3 -CH 2 -Cl + KOH \u003d CH 3 -CH 2 -OH + KCl
Classification of chemical reactions by changing the degree of oxidation of elements that form substances
By changing the oxidation state of elements chemical reactions are divided into redox reactions, and the reactions going no change in oxidation states chemical elements.
- Redox reactions (ORD) are reactions in which oxidation states substances change. In doing so, there is an exchange electrons.
AT inorganic chemistry such reactions include, as a rule, reactions of decomposition, substitution, compounds, and all reactions involving simple substances. To equalize the OVR, the method is used electronic balance(the number of donated electrons must be equal to the number received) or electron-ion balance method.
AT organic chemistry separate oxidation and reduction reactions, depending on what happens to the organic molecule.
Oxidation reactions in organic chemistry are reactions in which the number of hydrogen atoms decreases or the number of oxygen atoms in the original organic molecule increases.
for example, oxidation of ethanol under the action of copper oxide:
CH 3 -CH 2 -OH + CuO → CH 3 -CH \u003d O + H 2 O + Cu
Recovery reactions in organic chemistry, these are reactions in which the number of hydrogen atoms increases or the number of oxygen atoms decreases in an organic molecule.
for example, recovery acetaldehyde hydrogen:
CH 3 -CH \u003d O + H 2 → CH 3 -CH 2 -OH
- Protolytic reactions and exchange reactions - these are reactions in which the oxidation states of atoms do not change.
for example, neutralization caustic soda nitric acid:
NaOH + HNO 3 \u003d H 2 O + NaNO 3
Classification of reactions by thermal effect
According to the thermal effect, the reactions are divided into exothermic and endothermic.
exothermic reactions are reactions accompanied by the release of energy in the form of heat (+ Q). These reactions include almost all compound reactions.
Exceptions- reaction nitrogen with oxygen with education nitric oxide (II) - endothermic:
N 2 + O 2 \u003d 2NO - Q
Gaseous reaction hydrogen with hard iodine also endothermic:
H 2 + I 2 \u003d 2HI - Q
Exothermic reactions in which light is released are called reactions. burning.
for example, combustion of methane:
CH 4 + O 2 \u003d CO 2 + H 2 O
Also exothermic are:
Endothermic reactions are the reactions that energy absorption in the form of heat ( — Q ). As a rule, most reactions proceed with the absorption of heat. decomposition(reactions requiring prolonged heating).
for example, decomposition limestone:
CaCO 3 → CaO + CO 2 - Q
Also endothermic are:
- hydrolysis reactions;
- reactions that take place only when heated;
- reactions that take place onlyat very high temperatures or under the influence of an electrical discharge.
for example, the conversion of oxygen to ozone:
3O 2 \u003d 2O 3 - Q
AT organic chemistry With the absorption of heat, decomposition reactions take place. for example, cracking pentane:
C 5 H 12 → C 3 H 6 + C 2 H 6 - Q.
Classification of chemical reactions according to the state of aggregation of reacting substances (by phase composition)
Substances can exist in three main states of aggregation − solid, liquid and gaseous. By phase state share reactions homogeneous and heterogeneous.
- Homogeneous reactions are reactions in which the reactants and products are in one phase, and the collision of the reacting particles occurs in the entire volume of the reaction mixture. Homogeneous reactions include interactions liquid-liquid and gas-gas.
for example, oxidation sour gas:
2SO 2 (g) + O 2 (g) \u003d 2SO 3 (g)
- heterogeneous reactions are reactions in which the reactants and products are in different phases. In this case, the collision of reacting particles occurs only at the phase boundary. These reactions include interactions gas-liquid, gas-solid, solid-solid, and solid-liquid.
for example, interaction carbon dioxide and calcium hydroxide:
CO 2 (g) + Ca (OH) 2 (solution) \u003d CaCO 3 (tv) + H 2 O
To classify reactions according to the phase state, it is useful to be able to determine phase states of substances. This is quite easy to do, using knowledge about the structure of matter, in particular, about.
Substances with ionic, atomic or metallic crystal lattice , usually solid under normal conditions; substances with molecular lattice, usually, liquids or gases under normal conditions.
Please note that when heated or cooled, substances can change from one phase state to another. In this case, it is necessary to focus on the conditions for conducting a particular reaction and physical properties substances.
for example, receiving synthesis gas occurs at very high temperatures, at which water - steam:
CH 4 (g) + H2O (g) \u003d CO (g) + 3H 2 (g)
So steam reforming methane — homogeneous reaction.
Classification of chemical reactions according to the participation of a catalyst
A catalyst is a substance that speeds up a reaction but is not part of the reaction products. The catalyst participates in the reaction, but is practically not consumed during the reaction. Conventionally, the scheme of the catalyst To in the interaction of substances A+B can be depicted as follows: A + K = AK; AK + B = AB + K.
Depending on the presence of a catalyst, catalytic and non-catalytic reactions are distinguished.
- catalytic reactions are reactions that take place with the participation of catalysts. For example, the decomposition of Bertolet salt: 2KClO 3 → 2KCl + 3O 2.
- Non-catalytic reactions are reactions that take place without the participation of a catalyst. For example, combustion of ethane: 2C 2 H 6 + 5O 2 = 2CO 2 + 6H 2 O.
All reactions that occur with the participation of living organisms in the cells proceed with the participation of special protein catalysts - enzymes. Such reactions are called enzymatic.
The mechanism of action and functions of catalysts are considered in more detail in a separate article.
Classification of reactions by direction
Reversible reactions - these are reactions that can proceed both in the forward and in the reverse direction, i.e. when, under given conditions, the reaction products can interact with each other. Reversible reactions include most homogeneous reactions, esterification; hydrolysis reactions; hydrogenation-dehydrogenation, hydration-dehydration; production of ammonia from simple substances, oxidation of sulfur dioxide, production of hydrogen halides (except hydrogen fluoride) and hydrogen sulfide; methanol synthesis; obtaining and decomposition of carbonates and hydrocarbonates, etc.
irreversible reactions are reactions that proceed predominantly in one direction, i.e. reaction products cannot interact with each other under given conditions. Examples of irreversible reactions: combustion; explosive reactions; reactions proceeding with the formation of gas, precipitate or water in solutions; dissolution alkali metals in water; and etc.
chemical reactions- these are processes as a result of which others are formed from some substances, differing from them in composition and (or) structure.
Reaction classification:
I. According to the number and composition of the reactants and reaction products:
1) Reactions that take place without changing the composition of the substance:
In inorganic chemistry, these are reactions of transformation of some allotropic modifications into others:
C (graphite) → C (diamond); P (white) → P (red).
In organic chemistry, these are isomerization reactions - reactions, as a result of which molecules of other substances of the same qualitative and quantitative composition are formed from the molecules of one substance, i.e. with the same molecular formula but a different structure.
CH 2 -CH 2 -CH 3 → CH 3 -CH-CH 3
n-butane 2-methylpropane (isobutane)
2) Reactions that occur with a change in the composition of the substance:
a) Compound reactions (in organic chemistry of addition) - reactions during which one more complex is formed from two or more substances: S + O 2 → SO 2
In organic chemistry, these are the reactions of hydrogenation, halogenation, hydrohalogenation, hydration, and polymerization.
CH 2 \u003d CH 2 + HOH → CH 3 - CH 2 OH
b) Decomposition reactions (in organic chemistry, elimination, elimination) - reactions during which several new substances are formed from one complex substance:
CH 3 - CH 2 OH → CH 2 \u003d CH 2 + H 2 O
2KNO 3 →2KNO 2 + O 2
In organic chemistry, examples of cleavage reactions are dehydrogenation, dehydration, dehydrohalogenation, and cracking.
c) Substitution reactions - reactions in which atoms a simple substance replace the atoms of some element in a complex substance (in organic chemistry, two complex substances are often reactants and reaction products).
CH 4 + Cl 2 → CH 3 Cl + HCl; 2Na+ 2H 2 O → 2NaOH + H 2
Examples of substitution reactions that are not accompanied by a change in the oxidation states of atoms are extremely few. It should be noted the reaction of silicon oxide with salts of oxygen-containing acids, which correspond to gaseous or volatile oxides:
CaCO 3 + SiO 2 \u003d CaSiO 3 + CO 2
Ca 3 (RO 4) 2 + ZSiO 2 = ZCaSiO 3 + P 2 O 5
d) Exchange reactions - reactions during which two complex substances exchange their constituent parts:
NaOH + HCl → NaCl + H 2 O,
2CH 3 COOH + CaCO 3 → (CH 3 COO) 2 Ca + CO 2 + H 2 O
II. By changing the oxidation states of chemical elements that form substances
1) Reactions that occur with a change in oxidation states, or OVR:
∙2| N +5 + 3e - → N +2 (reduction process, element - oxidizing agent),
∙3| Cu 0 - 2e - → Cu +2 (oxidation process, element - reducing agent),
8HNO 3 + 3Cu → 3Cu(NO 3) 2 + 2NO + 4H 2 O.
In organic chemistry:
C 2 H 4 + 2KMnO 4 + 2H 2 O → CH 2 OH–CH 2 OH + 2MnO 2 + 2KOH
2) Reactions that take place without changing the oxidation states of chemical elements:
Li 2 O + H 2 O → 2LiOH,
HCOOH + CH 3 OH → HCOOCH 3 + H 2 O
III. By thermal effect
1) Exothermic reactions proceed with the release of energy:
C + O 2 → CO 2 + Q,
CH 4 + 2O 2 → CO 2 + 2H 2 O + Q
2) Endothermic reactions proceed with the absorption of energy:
СaCO 3 → CaO + CO 2 - Q
C 12 H 26 → C 6 H 14 + C 6 H 12 - Q
IV. By state of aggregation reactants
1) Heterogeneous reactions - reactions in which the reactants and reaction products are in different states of aggregation:
Fe(tv) + CuSO 4 (solution) → Cu(tv) + FeSO 4 (solution),
CaC 2 (tv) + 2H 2 O (l) → Ca (OH) 2 (solution) + C 2 H 2 (g)
2) Homogeneous reactions - reactions in which the reactants and reaction products are in the same state of aggregation:
H 2 (g) + Cl 2 (g) → 2HCl (g),
2C 2 H 2 (g) + 5O 2 (g) → 4CO 2 (g) + 2H 2 O (g)
v. According to the participation of the catalyst
1) Non-catalytic reactions that take place without the participation of a catalyst:
2H 2 + O 2 → 2H 2 O, C 2 H 4 + 3O 2 → 2CO 2 + 2H 2 O
2) Catalytic reactions taking place with the participation of catalysts:
2H 2 O 2 → 2H 2 O + O 2
VI. Towards
1) Irreversible reactions proceed under these conditions in only one direction:
C 2 H 4 + 3O 2 → 2CO 2 + 2H 2 O
2) Reversible reactions under these conditions proceed simultaneously in two opposite directions: N 2 + 3H 2 ↔2NH 3
VII. According to the flow mechanism
1) Radical mechanism.
A: B → A + + B
A homolytic (equivalent) bond cleavage occurs. During hemolytic rupture, a pair of electrons forming a bond is divided in such a way that each of the formed particles receives one electron. In this case, radicals are formed - uncharged particles with unpaired electrons. Radicals are very reactive particles, reactions involving them occur in the gas phase at high speed and often with an explosion.
Radical reactions take place between the radicals and molecules formed during the reaction:
2H 2 O 2 → 2H 2 O + O 2
CH 4 + Cl 2 → CH 3 Cl + HCl
Examples: combustion reactions of organic and non-organic organic matter, synthesis of water, ammonia, reactions of halogenation and nitration of alkanes, isomerization and aromatization of alkanes, catalytic oxidation of alkanes, polymerization of alkenes, vinyl chloride, etc.
2) Ionic mechanism.
A: B → :A - + B +
A heterolytic (unequal) bond breaking occurs, with both bond electrons remaining with one of the previously bonded species. Charged particles (cations and anions) are formed.
Ionic reactions go in solutions between ions already present or formed during the reaction.
For example, in inorganic chemistry this is the interaction of electrolytes in solution, in organic chemistry these are addition reactions to alkenes, oxidation and dehydrogenation of alcohols, substitution of the alcohol group and other reactions that characterize the properties of aldehydes and carboxylic acids.
VIII. According to the type of energy that initiates the reaction:
1) Photochemical reactions occur when exposed to light quanta. For example, the synthesis of hydrogen chloride, the interaction of methane with chlorine, the production of ozone in nature, the processes of photosynthesis, etc.
2) Radiation reactions are initiated by high-energy radiation (X-rays, γ-rays).
3) Electrochemical reactions initiates electricity such as in electrolysis.
4) Thermochemical reactions are initiated by thermal energy. These include all endothermic reactions and many exothermic ones that require heat to initiate.
Lesson goals. To generalize the idea of a chemical reaction as a process of transformation of one or more initial substances-reagents into substances that differ from them in chemical composition or structure - reaction products. Consider some of the many classifications of chemical reactions according to various criteria. Show the applicability of such classifications for inorganic and organic reactions. Reveal the relative nature of various types of chemical reactions and the relationship of various classifications of chemical processes.
The concept of chemical reactions, their classification according to various criteria in comparison for inorganic and organic substances
A chemical reaction is such a change in substances in which old chemical bonds are broken and new chemical bonds are formed between the particles (“volumes, ions) from which substances are built (slide 2).
Chemical reactions are classified:
1. By the number and composition of reagents and products (slide 3)
a) expansions (slide 4)
Decomposition reactions in organic chemistry, in contrast to decomposition reactions in inorganic chemistry, have their own specifics. They can be considered as the reverse processes of addition, since the result most often is the formation of multiple bonds or cycles.
b) connections (slide 5)
In order to enter into an addition reaction, organic molecule must have a multiple bond (or cycle), this molecule will be the main one (substrate). A simpler molecule (often an inorganic substance, a reagent) is attached at the site of a multiple bond break or ring opening.
c) substitutions (slide 6)
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 any atom or functional group in the molecule of the original substance 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.
d) exchange (including neutralization) (slide 7)
It is recommended to carry out in the form laboratory work according to the reaction equations proposed in the presentation
2. By thermal effect (slide 8)
a) endothermic
b) exothermic (including combustion reactions)
The presentation suggested reactions from inorganic and organic chemistry. Combination reactions will be exothermic reactions, and decomposition reactions will be endothermic (the relativity of this conclusion will be emphasized by a rare exception - the reaction of nitrogen with oxygen is endothermic:
N 2 + 0 2 -> 2
NO- Q
3. On the use of a catalyst (slide 9)
b) non-catalytic
4. Direction (slide 10)
a) catalytic (including enzymatic)
b) non-catalytic
5. By phase (slide 11)
a) homogeneous
b) heterogeneous
6. By changing the oxidation state of elements that form reactants and products (slide 12)
a) redox
b) without changing the oxidation state
Redox reactions in inorganic chemistry include all substitution reactions and those decomposition and compound reactions in which at least one simple substance is involved. In a more generalized version (already taking into account organic chemistry): all reactions involving simple substances. Conversely, reactions proceeding without changing the oxidation states of the elements that form the reactants and reaction products include all exchange reactions.
Consolidation of the studied topic (slide 13-21).
Summary of the lesson.
Lesson 2 Chemical properties, methods for obtaining saturated monobasic carboxylic acids "(Slide 1).Lesson goals. Give the concept of carboxylic acids and their classification in comparison with mineral acids. Consider the basics of international and trivial nomenclature and isomerism of this type organic compounds. Disassemble the structure of the carboxyl group and predict the chemical behavior of carboxylic acids. Consider general properties carboxylic acids in comparison with the properties of mineral acids. Give an idea of the special properties of carboxylic acids (radical reactions and the formation of functional derivatives). To acquaint students with the most characteristic representatives of carboxylic acids and show their significance in nature and in human life.
The concept of carboxylic acids, their classification according to various criteriacarboxylic acids- a class of organic compounds whose molecules contain a carboxyl group - COOH. The composition of limiting monobasic carboxylic acids corresponds to the general formula (Slide 2)
Carboxylic acids are classified:
According to the number of carboxyl groups carboxylic acids divided into (Slide 3):
- monocarboxylic or monobasic (acetic acid)
- dicarboxylic or dibasic (oxalic acid)
Depending on the structure of the hydrocarbon radical to which the carboxyl group is attached, carboxylic acids are divided into:
- aliphatic (acetic or acrylic)
- alicyclic (cyclohexanecarboxylic)
- aromatic (benzoic, phthalic)
Examples of acids (Slide 4)
Isomerism and structure of carboxylic acids
1. Isomerism of the carbon chain (Slide 5)
2. Isomerism of the position of a multiple bond, for example:
CH 2 \u003d CH - CH 2 - COOH Butene-3-oic acid (vinylacetic acid)
CH 3 - CH \u003d CH - COOH Butene-2-oic acid (crotonic acid)
3. Cis-, trans-isomerism, for example:
Structure(Slide 6)
The carboxyl group COOH consists of the carbonyl group C=O and the hydroxyl group OH.
In the CO group, the carbon atom carries a partial positive charge and attracts the electron pair of the oxygen atom in the OH group. In this case, the electron density on the oxygen atom decreases, and O-N connection weakened:
In turn, the OH group "extinguishes" the positive charge on the CO group.
Physical and chemical properties of carboxylic acids
Lower carboxylic acids are liquids with a pungent odor, highly soluble in water. With increasing relative molecular weight The solubility of acids in water decreases and the boiling point rises. Higher acids, starting with pelargonic
C 8 H 17 COOH - solids, odorless, insoluble in water.
The most important chemical properties characteristic of most carboxylic acids (Slide 7.8):
1) Interaction with active metals:
2 CH 3 COOH + Mg (CH 3 COO) 2 Mg + H 2
2) Interaction with metal oxides:
2CH 3 COOH + CaO (CH 3 COO) 2 Ca + H 2 O
3) Interaction with bases:
CH 3 COOH + NaOHCH 3 COONa + H 2 O
4) Interaction with salts:
CH 3 COOH + NaHCO 3 CH 3 COONa + CO 2 + H 2 O
5) Interaction with alcohols (esterification reaction):
CH 3 COOH + CH 3 CH 2 OHCH 3 COOSH 2 CH 3 + H 2 O
6) Interaction with ammonia:
CH 3 COOH + NH 3 CH 3 COONH 4
When heated, ammonium salts of carboxylic acids form their amides:
CH 3 COONH 4 CH 3 CONH 2 + H 2 O
7) Under the action of SOC l2, carboxylic acids are converted into the corresponding acid chlorides.
CH 3 COOH + SOC l2 CH 3 COCl + HCl + SO 2
4. Interclass isomerism :
for example: C 4 H 8 O 2
CH 3 - CH 2 - CO - O - CH 3 propanoic acid methyl ester
CH 3 - CO - O - CH 2 - CH 3 ethanoic acid ethyl ester
С3Н 7 - COOH butanoic acid
(Slide 9,10)
1. Oxidation of aldehydes and primary alcohols -
general method for obtaining carboxylic acids:
2. Another general method is the hydrolysis of halogenated hydrocarbons containing three halogen atoms on one carbon atom:
3
NaCl
3. Interaction of the Grignard reagent with CO2:
4. Hydrolysis esters:
5. Hydrolysis of acid anhydrides:
Methods for obtaining carboxylic acids
For individual acids there are specific ways to obtain (Slide 11):
To receive benzoic acid you can use the oxidation of monosubstituted benzene homologues with an acidic solution of potassium permanganate:
Acetic acid obtained on an industrial scale by catalytic oxidation of butane with atmospheric oxygen:
Formic acid obtained by heating carbon monoxide (II) with powdered sodium hydroxide under pressure and processing the resulting sodium formate with a strong acid:
Application of carboxylic acids(Slide 12)
Consolidation of the studied topic (slide 13-14).
Classification of chemical reactions in inorganic and organic chemistry
Chemical reactions, or chemical phenomena, are processes as a result of which others are formed from some substances, differing 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.
Chemical reactions should be distinguished from nuclear reactions. As a result of a chemical reaction total number atoms of each chemical element and its isotopic composition do not change. Another thing nuclear reactions- transformation processes atomic nuclei as a result of their interaction with other nuclei or elementary particles, for example, the conversion of aluminum to magnesium:
$↙(13)↖(27)(Al)+ ()↙(1)↖(1)(H)=()↙(12)↖(24)(Mg)+()↙(2)↖(4 )(He)$
The classification of chemical reactions is multifaceted, i.e. It can be based on various features. But under any of these signs, reactions both between inorganic and between organic substances can be attributed.
Consider the classification of chemical reactions according to various criteria.
Classification of chemical reactions according to the number and composition of reactants. Reactions that take place without changing the composition of the substance
In inorganic chemistry, such reactions include the processes of obtaining allotropic modifications of one chemical element, for example:
$С_((graphite))⇄С_((diamond))$
$S_((rhombic))⇄S_((monoclinic))$
$P_((white))⇄P_((red))$
$Sn_((white tin))⇄Sn_((grey tin))$
$3O_(2(oxygen))⇄2O_(3(ozone))$.
In organic chemistry, this type of reactions can include isomerization reactions that occur without changing not only the qualitative, but also the quantitative composition of the molecules of substances, for example:
1. Isomerization of alkanes.
The reaction of isomerization of alkanes is of great practical importance, because. isostructure hydrocarbons are less prone to detonation.
2. Alkene isomerization.
3. Alkyne isomerization(reaction of A. E. Favorsky).
4. Isomerization of haloalkanes(A. E. Favorsky).
5. Isomerization of ammonium cyanate on heating.
For the first time, urea was synthesized by F. Wehler in 1882 by isomerization of ammonium cyanate when heated.
Reactions that go with a change in the composition of a substance
There are four types of such reactions: compounds, decompositions, substitutions and exchanges.
1. Connection reactions- These are reactions in which two or more substances form one complex substance.
In inorganic chemistry, the whole variety of compound reactions can be considered using the example of reactions for obtaining sulfuric acid from sulfur:
1) obtaining sulfur oxide (IV):
$S+O_2=SO_2$ — one complex substance is formed from two simple substances;
2) production of sulfur oxide (VI):
$2SO_2+O_2(⇄)↖(t,p,cat.)2SO_3$ - one complex substance is formed from simple and complex substances;
3) obtaining sulfuric acid:
$SO_3+H_2O=H_2SO_4$ — one compound is formed from two complex substances.
An example of a compound reaction in which one complex substance is formed from more than two starting materials is the final stage in the production of nitric acid:
$4NO_2+O_2+2H_2O=4HNO_3$.
In organic chemistry, compound reactions are commonly referred to as addition reactions. The whole variety of such reactions can be considered on the example of a block of reactions characterizing the properties of unsaturated substances, for example, ethylene:
1) hydrogenation reaction - addition of hydrogen:
$CH_2(=)↙(ethene)CH_2+H_2(→)↖(Ni,t°)CH_3(-)↙(ethane)CH_3;$
2) hydration reaction - addition of water:
$CH_2(=)↙(ethene)CH_2+H_2O(→)↖(H_3PO_4,t°)(C_2H_5OH)↙(ethanol);$
3) polymerization reaction:
$(nCH_2=CH_2)↙(ethylene)(→)↖(p,cat.,t°)((-CH_2-CH_2-)_n)↙(polyethylene)$
2. Decomposition reactions These are reactions in which several new substances are formed from one complex substance.
In inorganic chemistry, the whole variety of such reactions can be considered using the example of a block of reactions for obtaining oxygen by laboratory methods:
1) decomposition of mercury oxide (II):
$2HgO(→)↖(t°)2Hg+O_2$ — two simple substances are formed from one complex substance;
2) decomposition of potassium nitrate:
$2KNO_3(→)↖(t°)2KNO_2+O_2$ — from one complex substance one simple and one complex substance are formed;
3) decomposition of potassium permanganate:
$2KMnO_4(→)↖(t°)K_2MnO_4+MnO_2+O_2$ — from one complex substance two complex and one simple are formed, i.e. three new substances.
In organic chemistry, decomposition reactions can be considered using the example of a block of reactions for the production of ethylene in the laboratory and industry:
1) the reaction of dehydration (water splitting) of ethanol:
$C_2H_5OH(→)↖(H_2SO_4,t°)CH_2=CH_2+H_2O;$
2) the reaction of dehydrogenation (hydrogen elimination) of ethane:
$CH_3—CH_3(→)↖(Cr_2O_3,500°C)CH_2=CH_2+H_2;$
3) propane cracking (splitting) reaction:
$CH_3-CH_2CH_3(→)↖(t°)CH_2=CH_2+CH_4.$
3. Substitution reactions- these are reactions in which the atoms of a simple substance replace the atoms of an element in a complex substance.
In inorganic chemistry, an example of such processes is a block of reactions that characterize the properties of, for example, metals:
1) interaction of alkali and alkaline earth metals with water:
$2Na+2H_2O=2NaOH+H_2$
2) interaction of metals with acids in solution:
$Zn+2HCl=ZnCl_2+H_2$;
3) interaction of metals with salts in solution:
$Fe+CuSO_4=FeSO_4+Cu;$
4) metallothermy:
$2Al+Cr_2O_3(→)↖(t°)Al_2O_3+2Cr$.
The subject of study of organic chemistry is not simple substances, but only compounds. Therefore, as an example of a substitution reaction, we present the most characteristic property limiting compounds, in particular methane, is the ability of its hydrogen atoms to be replaced by halogen atoms:
$CH_4+Cl_2(→)↖(hν)(CH_3Cl)↙(chloromethane)+HCl$,
$CH_3Cl+Cl_2→(CH_2Cl_2)↙(dichloromethane)+HCl$,
$CH_2Cl_2+Cl_2→(CHCl_3)↙(trichloromethane)+HCl$,
$CHCl_3+Cl_2→(CCl_4)↙(tetrachloromethane)+HCl$.
Another example is bromination aromatic compound(benzene, toluene, aniline):
Let us pay attention to the peculiarity of substitution reactions in organic substances: as a result of such reactions, not a simple and complex substance is formed, as in inorganic chemistry, but two complex substances.
In organic chemistry, substitution reactions also include some reactions between two complex substances, for example, the nitration of benzene:
$C_6H_6+(HNO_3)↙(benzene)(→)↖(H_2SO_4(conc.),t°)(C_6H_5NO_2)↙(nitrobenzene)+H_2O$
It is formally an exchange reaction. The fact that this is a substitution reaction becomes clear only when considering its mechanism.
4. Exchange reactions- these are reactions in which two complex substances exchange their constituent parts.
These reactions characterize the properties of electrolytes and proceed in solutions according to the Berthollet rule, i.e. only if the result is a precipitate, a gas, or a low-dissociation substance (for example, $H_2O$).
In inorganic chemistry, this can be a block of reactions characterizing, for example, the properties of alkalis:
1) a neutralization reaction that goes with the formation of salt and water:
$NaOH+HNO_3=NaNO_3+H_2O$
or in ionic form:
$OH^(-)+H^(+)=H_2O$;
2) the reaction between alkali and salt, which goes with the formation of gas:
$2NH_4Cl+Ca(OH)_2=CaCl_2+2NH_3+2H_2O$
or in ionic form:
$NH_4^(+)+OH^(-)=NH_3+H_2O$;
3) the reaction between alkali and salt, which proceeds with the formation of a precipitate:
$CuSO_4+2KOH=Cu(OH)_2↓+K_2SO_4$
or in ionic form:
$Cu^(2+)+2OH^(-)=Cu(OH)_2↓$
In organic chemistry, one can consider a block of reactions characterizing, for example, the properties of acetic acid:
1) a reaction proceeding with the formation of a weak electrolyte - $H_2O$:
$CH_3COOH+NaOH⇄NaCH_3COO+H_2O$
$CH_3COOH+OH^(-)⇄CH_3COO^(-)+H_2O$;
2) the reaction proceeding with the formation of gas:
$2CH_3COOH+CaCO_3=2CH_3COO^(-)+Ca^(2+)+CO_2+H_2O$;
3) reaction proceeding with the formation of a precipitate:
$2CH_3COOH+K_2SiO_3=2KCH_3COO+H_2SiO_3↓$
$2CH_3COOH+SiO_3^(−)=2CH_3COO^(−)+H_2SiO_3↓$.
Classification of chemical reactions according to the change in the oxidation states of chemical elements that form substances
Reactions that occur with a change in the oxidation states of elements, or redox reactions.
These include many reactions, including all substitution reactions, as well as those reactions of combination and decomposition in which at least one simple substance participates, for example:
1.$(Mg)↖(0)+(2H)↖(+1)+SO_4^(-2)=(Mg)↖(+2)SO_4+(H_2)↖(0)$
$((Mg)↖(0)-2(e)↖(-))↙(reducing agent)(→)↖(oxidation)(Mg)↖(+2)$
$((2H)↖(+1)+2(e)↖(-))↙(oxidizer)(→)↖(reduction)(H_2)↖(0)$
2.$(2Mg)↖(0)+(O_2)↖(0)=(2Mg)↖(+2)(O)↖(-2)$
$((Mg)↖(0)-2(e)↖(-))↙(reductant)(→)↖(oxidation)(Mg)↖(+2)|4|2$
$((O_2)↖(0)+4(e)↖(-))↙(oxidizer)(→)↖(reduction)(2O)↖(-2)|2|1$
As you remember, complex redox reactions are compiled using the electron balance method:
$(2Fe)↖(0)+6H_2(S)↖(+6)O_(4(k))=(Fe_2)↖(+3)(SO_4)_3+3(S)↖(+4)O_2+ 6H_2O$
$((Fe)↖(0)-3(e)↖(-))↙(reducing agent)(→)↖(oxidation)(Fe)↖(+3)|2$
$((S)↖(+6)+2(e)↖(-))↙(oxidizer)(→)↖(reduction)(S)↖(+4)|3$
In organic chemistry a prime example properties of aldehydes can serve as redox reactions:
1. Aldehydes are reduced to the corresponding alcohols:
$(CH_3-(C)↖(+1) ()↖(O↖(-2))↙(H↖(+1))+(H_2)↖(0))↙(\text"acetaldehyde") (→)↖(Ni,t°)(CH_3-(C)↖(-1)(H_2)↖(+1)(O)↖(-2)(H)↖(+1))↙(\text "ethyl alcohol")$
$((C)↖(+1)+2(e)↖(-))↙(oxidizer)(→)↖(reduction)(C)↖(-1)|1$
$((H_2)↖(0)-2(e)↖(-))↙(reductant)(→)↖(oxidation)2(H)↖(+1)|1$
2. Aldehydes are oxidized to the corresponding acids:
$(CH_3-(C)↖(+1) ()↖(O↖(-2))↙(H↖(+1))+(Ag_2)↖(+1)(O)↖(-2)) ↙(\text"acetaldehyde")(→)↖(t°)(CH_3-(Ag)↖(0)(C)↖(+3)(O)↖(-2)(OH)↖(-2 +1)+2(Ag)↖(0)↓)↙(\text"ethyl alcohol")$
$((C)↖(+1)-2(e)↖(-))↙(reducing agent)(→)↖(oxidation)(C)↖(+3)|1$
$(2(Ag)↖(+1)+2(e)↖(-))↙(oxidizer)(→)↖(reduction)2(Ag)↖(0)|1$
Reactions that take place without changing the oxidation states of chemical elements.
These include, for example, all ion exchange reactions, as well as:
- many compound reactions:
$Li_2O+H_2O=2LiOH;$
- many decomposition reactions:
$2Fe(OH)_3(→)↖(t°)Fe_2O_3+3H_2O;$
- esterification reactions:
$HCOOH+CH_3OH⇄HCOOCH_3+H_2O$.
Classification of chemical reactions by thermal effect
According to the thermal effect, the reactions are divided into exothermic and endothermic.
exothermic reactions.
These reactions proceed with the release of energy.
These include almost all compound reactions. A rare exception is the endothermic reactions of the synthesis of nitric oxide (II) from nitrogen and oxygen and the reaction of gaseous hydrogen with solid iodine:
$N_2+O_2=2NO - Q$,
$H_(2(t))+I(2(t))=2HI - Q$.
Exothermic reactions that proceed with the release of light are referred to as combustion reactions, for example:
$4P+5O_2=2P_2O_5+Q,$
$CH_4+2O_2=CO_2+2H_2O+Q$.
The hydrogenation of ethylene is an example of an exothermic reaction:
$CH_2=CH_2+H_2(→)↖(Pt)CH_3-CH_3+Q$
It runs at room temperature.
Endothermic reactions
These reactions proceed with the absorption of energy.
Obviously, almost all decomposition reactions belong to them, for example:
a) burning limestone:
$CaCO_3(→)↖(t°)CaO+CO_2-Q;$
b) butane cracking:
The amount of energy released or absorbed in a reaction is called the thermal effect of the reaction, and the equation of a chemical reaction indicating this effect is called thermochemical equation, For example:
$H_(2(g))+Cl_(2(g))=2HCl_((g))+92.3 kJ,$
$N_(2(g))+O_(2(g))=2NO_((g)) - 90.4 kJ$.
Classification of chemical reactions according to the state of aggregation of reacting substances (phase composition)
heterogeneous reactions.
These are reactions in which the reactants and reaction products are in different states of aggregation (in different phases):
$2Al_((m))+3CuCl_(2(r-r))=3Cu_((t))+2AlCl_(3(r-r))$,
$CaC_(2(t))+2H_2O_((l))=C_2H_2+Ca(OH)_(2(solid))$.
homogeneous reactions.
These are reactions in which the reactants and reaction products are in the same state of aggregation (in the same phase):
Classification of chemical reactions according to the participation of a catalyst
non-catalytic reactions.
Non-catalytic reactions go without the participation of a catalyst:
$2HgO(→)↖(t°)2Hg+O_2$,
$C_2H_4+3O_2(→)↖(t°)2CO_2+2H_2O$.
catalytic reactions.
catalytic reactions going on with a catalyst:
$2KClO_3(→)↖(MnO_2,t°)2KCl+3O_2,$
$(C_2H_5OH)↙(ethanol)(→)↖(H_2SO-4,t°)(CH_2=CH_2)↙(ethene)+H_2O$
Since all biological reactions occurring in the cells of living organisms proceed with the participation of special biological catalysts of a protein nature - enzymes, they all belong to catalytic or, more precisely, enzymatic.
It should be noted that more than $70%$ of chemical industries use catalysts.
Classification of chemical reactions by direction
irreversible reactions.
irreversible reactions flow under these conditions in only one direction.
These include all exchange reactions accompanied by the formation of a precipitate, gas or a low-dissociating substance (water), and all combustion reactions.
reversible reactions.
Reversible reactions under these conditions proceed simultaneously in two opposite directions.
Most of these reactions are.
In organic chemistry, the sign of reversibility is reflected in the names-antonyms of processes:
- hydrogenation - dehydrogenation;
- hydration - dehydration;
- polymerization - depolymerization.
All esterification reactions are reversible (the opposite process, as you know, is called hydrolysis) and hydrolysis of proteins, esters, carbohydrates, polynucleotides. Reversibility underlies the most important process in a living organism - metabolism.
chemical reactions- these are processes as a result of which others are formed from some substances, differing from them in composition and (or) structure.
Reaction classification:
According to the number and composition of the reactants and reaction products:
Reactions that take place without changing the composition of the substance:
C (graphite) → C (diamond); P (white) → P (red).
In organic chemistry, these are isomerization reactions - reactions, as a result of which molecules of other substances of the same qualitative and quantitative composition are formed from the molecules of one substance, i.e. with the same molecular formula but a different structure.
CH 2 -CH 2 -CH 3 → CH 3 -CH-CH 3
n-butane 2-methylpropane (isobutane)
Reactions that occur with a change in the composition of a substance:
In organic chemistry, these are the reactions of hydrogenation, halogenation, hydrohalogenation, hydration, and polymerization.
CH 2 \u003d CH 2 + HOH → CH 3 - CH 2 OH
b) Decomposition reactions (in organic chemistry, elimination, elimination) - reactions during which several new substances are formed from one complex substance:
CH 3 - CH 2 OH → CH 2 \u003d CH 2 + H 2 O
2KNO 3 →2KNO 2 + O 2
In organic chemistry, examples of cleavage reactions are dehydrogenation, dehydration, dehydrohalogenation, cracking.
c) Substitution reactions - reactions in which atoms of a simple substance replace the atoms of an element in a complex substance (in organic chemistry, two complex substances are often reactants and reaction products).
CH 4 + Cl 2 → CH 3 Cl + HCl; 2Na+ 2H 2 O → 2NaOH + H 2
Examples of substitution reactions that are not accompanied by a change in the oxidation states of atoms are extremely few. It should be noted the reaction of silicon oxide with salts of oxygen-containing acids, which correspond to gaseous or volatile oxides:
CaCO 3 + SiO 2 \u003d CaSiO 3 + CO 2
Ca 3 (RO 4) 2 + ZSiO 2 = ZCaSiO 3 + P 2 O 5
d) Exchange reactions - reactions during which two complex substances exchange their constituent parts:
NaOH + HCl → NaCl + H 2 O,
2CH 3 COOH + CaCO 3 → (CH 3 COO) 2 Ca + CO 2 + H 2 O
By changing the oxidation states of chemical elements that form substances
Reactions that go with a change in oxidation states, or OVR:
∙3| Cu 0 - 2e - → Cu +2 (oxidation process, element - reducing agent),
8HNO 3 + 3Cu → 3Cu(NO 3) 2 + 2NO + 4H 2 O.
In organic chemistry:
C 2 H 4 + 2KMnO 4 + 2H 2 O → CH 2 OH–CH 2 OH + 2MnO 2 + 2KOH
Reactions that take place without changing the oxidation states of chemical elements:
HCOOH + CH 3 OH → HCOOCH 3 + H 2 O
By thermal effect
Exothermic reactions proceed with the release of energy:
CH 4 + 2O 2 → CO 2 + 2H 2 O + Q
Endothermic reactions proceed with the absorption of energy:
C 12 H 26 → C 6 H 14 + C 6 H 12 - Q
According to the state of aggregation of the reactants
Heterogeneous reactions - reactions in which the reactants and reaction products are in different states of aggregation:
CaC 2 (tv) + 2H 2 O (l) → Ca (OH) 2 (solution) + C 2 H 2 (g)
Homogeneous reactions - reactions in which the reactants and reaction products are in the same state of aggregation:
2C 2 H 2 (g) + 5O 2 (g) → 4CO 2 (g) + 2H 2 O (g)
According to the participation of the catalyst
Non-catalytic reactions that take place without the participation of a catalyst:
Catalytic reactions that take place with the participation of catalysts:
2H 2 O 2 → 2H 2 O + O 2
Towards
Irreversible reactions proceed under these conditions in only one direction:
Reversible reactions under these conditions proceed simultaneously in two opposite directions: N 2 + 3H 2 ↔2NH 3
According to the flow mechanism
radical mechanism.
A homolytic (equivalent) bond cleavage occurs. During hemolytic rupture, a pair of electrons forming a bond is divided in such a way that each of the formed particles receives one electron. In this case, radicals are formed - uncharged particles with unpaired electrons. Radicals are very reactive particles, reactions involving them occur in the gas phase at high speed and often with an explosion.
Radical reactions take place between the radicals and molecules formed during the reaction:
2H 2 O 2 → 2H 2 O + O 2
CH 4 + Cl 2 → CH 3 Cl + HCl
Examples: combustion reactions of organic and inorganic substances, synthesis of water, ammonia, reactions of halogenation and nitration of alkanes, isomerization and aromatization of alkanes, catalytic oxidation of alkanes, polymerization of alkenes, vinyl chloride, etc.
Ionic mechanism.
A heterolytic (unequal) bond breaking occurs, with both bond electrons remaining with one of the previously bonded species. Charged particles (cations and anions) are formed.
Ionic reactions take place in solutions between ions already present or formed during the reaction.
For example, in inorganic chemistry this is the interaction of electrolytes in solution, in organic chemistry these are addition reactions to alkenes, oxidation and dehydrogenation of alcohols, substitution of the alcohol group and other reactions that characterize the properties of aldehydes and carboxylic acids.
According to the type of energy that initiates the reaction:
Photochemical reactions occur when exposed to light quanta. For example, the synthesis of hydrogen chloride, the interaction of methane with chlorine, the production of ozone in nature, the processes of photosynthesis, etc.
Radiation reactions are initiated by high-energy radiation (X-rays, γ-rays).
Electrochemical reactions are initiated by an electric current, for example, during electrolysis.
Thermochemical reactions are initiated by thermal energy. These include all endothermic reactions and many exothermic ones that require heat to initiate.
