During chemical reactions, one substance produces another (not to be confused with nuclear reactions, in which one chemical element turns into another).
Any chemical reaction is described by a chemical equation:
Reactants → Reaction products
The arrow indicates the direction of the reaction.
For example:
In this reaction, methane (CH 4) reacts with oxygen (O 2), resulting in the formation of carbon dioxide (CO 2) and water (H 2 O), or more precisely, water vapor. This is exactly the reaction that happens in your kitchen when you light a gas burner. The equation should be read like this: One molecule of methane gas reacts with two molecules of oxygen gas to produce one molecule of carbon dioxide and two molecules of water (water vapor).
The numbers placed before the components of a chemical reaction are called reaction coefficients.
Chemical reactions happen endothermic(with energy absorption) and exothermic(with energy release). Methane combustion - typical example exothermic reaction.
There are several types of chemical reactions. The most common:
- connection reactions;
- decomposition reactions;
- single replacement reactions;
- double displacement reactions;
- oxidation reactions;
- redox reactions.
Compound reactions
In compound reactions, at least two elements form one product:
2Na (t) + Cl 2 (g) → 2NaCl (t)- formation of table salt.
Attention should be paid to an essential nuance of compound reactions: depending on the conditions of the reaction or the proportions of the reagents entering the reaction, its result may be different products. For example, when normal conditions combustion coal carbon dioxide is produced:
C (t) + O 2 (g) → CO 2 (g)
If the amount of oxygen is insufficient, then a deadly substance is formed. carbon monoxide:
2C (t) + O 2 (g) → 2CO (g)
Decomposition reactions
These reactions are, as it were, essentially opposite to the reactions of the compound. As a result of the decomposition reaction, the substance breaks down into two (3, 4...) simpler elements (compounds):
- 2H 2 O (l) → 2H 2 (g) + O 2 (g)- water decomposition
- 2H 2 O 2 (l) → 2H 2 (g) O + O 2 (g)- decomposition of hydrogen peroxide
Single displacement reactions
As a result of single substitution reactions, a more active element replaces a less active one in a compound:
Zn (s) + CuSO 4 (solution) → ZnSO 4 (solution) + Cu (s)
Zinc in a copper sulfate solution displaces the less active copper, resulting in the formation of a zinc sulfate solution.
The degree of activity of metals in increasing order of activity:
- The most active are alkali and alkaline earth metals
The ionic equation for the above reaction will be:
Zn (t) + Cu 2+ + SO 4 2- → Zn 2+ + SO 4 2- + Cu (t)
The ionic bond CuSO 4, when dissolved in water, breaks down into a copper cation (charge 2+) and a sulfate anion (charge 2-). As a result of the substitution reaction, a zinc cation is formed (which has the same charge as the copper cation: 2-). Please note that the sulfate anion is present on both sides of the equation, i.e., according to all the rules of mathematics, it can be reduced. The result is an ion-molecular equation:
Zn (t) + Cu 2+ → Zn 2+ + Cu (t)
Double displacement reactions
In double substitution reactions, two electrons are already replaced. Such reactions are also called exchange reactions. Such reactions take place in solution with the formation of:
- insoluble solid (precipitation reaction);
- water (neutralization reaction).
Precipitation reactions
When a solution of silver nitrate (salt) is mixed with a solution of sodium chloride, silver chloride is formed:
Molecular equation: KCl (solution) + AgNO 3 (p-p) → AgCl (s) + KNO 3 (p-p)
Ionic equation: K + + Cl - + Ag + + NO 3 - → AgCl (t) + K + + NO 3 -
Molecular ionic equation: Cl - + Ag + → AgCl (s)
If a compound is soluble, it will be present in solution in ionic form. If the compound is insoluble, it will precipitate to form a solid.
Neutralization reactions
These are reactions between acids and bases that result in the formation of water molecules.
For example, the reaction of mixing a solution of sulfuric acid and a solution of sodium hydroxide (lye):
Molecular equation: H 2 SO 4 (p-p) + 2NaOH (p-p) → Na 2 SO 4 (p-p) + 2H 2 O (l)
Ionic equation: 2H + + SO 4 2- + 2Na + + 2OH - → 2Na + + SO 4 2- + 2H 2 O (l)
Molecular ionic equation: 2H + + 2OH - → 2H 2 O (l) or H + + OH - → H 2 O (l)
Oxidation reactions
These are reactions of interaction of substances with gaseous oxygen in the air, in which, as a rule, a large number of energy in the form of heat and light. Typical reaction oxidation is combustion. At the very beginning of this page is the reaction between methane and oxygen:
CH 4 (g) + 2O 2 (g) → CO 2 (g) + 2H 2 O (g)
Methane belongs to hydrocarbons (compounds of carbon and hydrogen). When a hydrocarbon reacts with oxygen, a lot of thermal energy is released.
Redox reactions
These are reactions in which electrons are exchanged between reactant atoms. The reactions discussed above are also redox reactions:
- 2Na + Cl 2 → 2NaCl - compound reaction
- CH 4 + 2O 2 → CO 2 + 2H 2 O - oxidation reaction
- Zn + CuSO 4 → ZnSO 4 + Cu - single substitution reaction
Redox reactions with a large number of examples of solving equations using the electron balance method and the half-reaction method are described in as much detail as possible in the section
Test No. 2.
Explore Chapter 2 "The Origin of Life on Earth""pages 30-80 of the textbook" General biology. 10th grade” author, etc.
I. Answer the questions in writing:
1. What are the foundations and essence of life according to ancient Greek philosophers?
2. What is the meaning of F. Redi's experiments?
3. Describe L. Pasteur’s experiments proving the impossibility of spontaneous generation of life under modern conditions.
4.What are theories of the eternity of life?
5.What materialistic theories of the origin of life do you know?
What are nuclear fusion reactions? Give examples.
6. How, in accordance with the Kant-Laplace hypothesis, are star systems formed from gas-dust matter?
7. Are there differences in the chemical composition of planets of the same star system?
8. List the cosmic and planetary prerequisites for the emergence of life abiogenically on our planet.
9.What is the significance for the emergence of organic molecules from non organic matter on Earth had the reducing nature of the primary atmosphere?
10.Describe the apparatus and methods of conducting experiments by S. Miller and P. Ury.
11. What is coacervation, coacervate?
12. Which ones model systems can you demonstrate the formation of coacervate droplets in solution?
13.What are the opportunities to overcome low concentrations organic substances existed in the waters of the primary ocean?
14. What are the advantages for the interaction of organic molecules in zones high concentrations substances?
15. How could they be distributed in the waters of the primary ocean? organic molecules, having hydrophilic and hydrophobic properties?.
16. Name the principle of dividing a solution into phases with high and low concentrations of molecules. ?
17. What are coacervate drops?
18. How does the selection of coacervates occur in the “primary broth”?
19. What is the essence of the hypothesis of the emergence of eukaryotes through symbiogenesis?
20. In what ways did the first eukaryotic cells obtain the energy necessary for vital processes?
21. Which organisms developed the sexual process for the first time in the process of evolution?
22. Describe the essence of the hypothesis about the emergence of multicellular organisms?
23. Define the following terms: protobionts, biological catalysts, genetic code, self-reproduction, prokaryotes, photosynthesis, sexual process, eukaryotes.
Test your knowledge on the topic:
Origin of life and development of the organic world
1. Proponents of biogenesis argue that
· All living things are from living things
· All living things are created by God
· All living things come from non-living things
· Living organisms were brought to Earth from the Universe
2. Proponents of abiogenesis argue that everything is living
· Comes from non-living
·Arises from living things
· Created by God
·Brought from space
3. Experiments by L. Pasteur using flasks with an elongated neck
· Proved the inconsistency of the position of abiogenesis
· Affirmed the position of abiogenesis
· Affirmed the position of biogenesis
· Proved the inconsistency of the position of biogenesis
4. Proof that life does not arise spontaneously was provided by
· L. Pasteur
· A. Van Leeuwenhoek
· Aristotle
5. Aristotle believed that
· Living only from living
· Life arises from four elements
· Living things come from non-living things
· Living things can come from non-living things if they have an “active principle”
6. Hypothesis
· Strengthens the position of supporters of biogenesis
· Strengthens the position of supporters of abiogenesis
· Emphasizes the inconsistency of the position of biogenesis
· Emphasizes the inconsistency of the position of abiogenesis
7. According to the hypothesis, coacervates are the first
Organisms
"Organizations" of molecules
· Protein complexes
Accumulations of inorganic substances
8. At the stage of chemical evolution, they are formed
· Bacteria
· Protobionts
· Biopolymers
Low molecular weight organic compounds
9. At the stage biological evolution are formed
· Biopolymers
Organisms
Low molecular weight organic substances
· Inorganic substances
1. By modern ideas life on earth developed as a result
Chemical evolution
Biological evolution
· Chemical and then biological evolution
Chemical and biological evolution
Biological and then chemical evolution
10. The first organisms to appear on Earth ate
Autotrophs
Heterotrophs
· Saprophytes
11. As a result of the appearance of autotrophs in the Earth's atmosphere
Increased amount of oxygen
· Decreased amount of oxygen
· The number has increased carbon dioxide
· Ozone screen appeared
12. Quantity organic compounds in the primary ocean decreased due to
Increase in the number of autotrophs
Increase in the number of heterotrophs
Reducing the number of autotrophs
· Decrease in the number of heterotrophs
13. The accumulation of oxygen in the atmosphere occurred due to
· The appearance of the ozone screen
· Photosynthesis
· Fermentation
· The cycle of substances in nature
14. The process of Photosynthesis led to
· Formation of large amounts of oxygen
· The appearance of the ozone screen
The emergence of multicellularity
The emergence of sexual reproduction
15. Check the correct statements:
Heterotrophs - organisms capable of independently synthesizing organic substances from inorganic ones
· The first organisms on Earth were heterotrophic
Cyanobacteria – the first photosynthetic organisms
· The mechanism of photosynthesis was formed gradually
16. Breakdown of organic compounds under oxygen-free conditions:
· Fermentation
· Photosynthesis
Oxidation
Biosynthesis
17. With the appearance of autotrophs on Earth:
Irreversible changes in the conditions of life have begun
A large amount of oxygen was formed in the atmosphere
· There was an accumulation of solar energy in the chemical bonds of organic substances
· All heterotrophs disappeared
18. Man appeared on Earth in
Proterozoic era
Mesozoic era
· Cenozoic era
Proterozoic
Mesozoic
· Paleozoic
Cenozoic
20. The largest events of the Proterozoic are considered
· Emergence of eukaryotes
The appearance of flowering plants
The emergence of the first chordates
21. The process of soil formation on Earth occurred thanks to
· The water cycle in nature
· Colonization of the upper layer of the lithosphere by organisms
The death of organisms
· Destruction of hard rocks with the formation of sand and clay
22. They were widespread in Archean
Reptiles and ferns
· Bacteria and cyanobacteria
23. Plants, animals and fungi came to land in
Proterozoic
· Paleozoic
Mesozoic
24. Proterozoic era
Mammals and insects
Algae and coelenterates
· First land plants
· Dominance of reptiles
About atoms and chemical elements
There is nothing else in nature
neither here nor there, in the depths of space:
everything - from small grains of sand to planets -
consists of unified elements.
S. P. Shchipachev, “Reading Mendeleev.”
In chemistry, except for terms "atom" And "molecule" the concept is often used "element". What do these concepts have in common and how do they differ?
Chemical element – these are atoms of the same type . So, for example, all hydrogen atoms are the element hydrogen; all oxygen and mercury atoms are the elements oxygen and mercury, respectively.
Currently, more than 107 types of atoms are known, that is, more than 107 chemical elements. It is necessary to distinguish between the concepts of “chemical element”, “atom” and “simple substance”
Simple and complex substances
According to their elemental composition they are distinguished simple substances, consisting of atoms of one element (H 2, O 2, Cl 2, P 4, Na, Cu, Au), and complex substances, consisting of atoms of different elements (H 2 O, NH 3, OF 2, H 2 SO 4, MgCl 2, K 2 SO 4).
Currently, 115 chemical elements are known, which form about 500 simple substances.
Native gold is a simple substance.
The ability of one element to exist in the form of different simple substances, differing in properties, is called allotropy For example, the element oxygen O has two allotropic forms - dioxygen O 2 and ozone O 3 with different numbers of atoms in the molecules.
Allotropic forms of the element carbon C - diamond and graphite - differ in the structure of their crystals. There are other reasons for allotropy.
chemical compounds, for example, mercury(II) oxide HgO (obtained by combining atoms of simple substances - mercury Hg and oxygen O 2), sodium bromide (obtained by combining atoms of simple substances - sodium Na and bromine Br 2).
So, let's summarize the above. There are two types of molecules of matter:
1. Simple– the molecules of such substances consist of atoms of the same type. In chemical reactions they cannot decompose to form several simpler substances.
2. Complex- molecules of such substances consist of atoms different types. In chemical reactions they can decompose to form simpler substances.
The difference between the concepts of “chemical element” and “simple substance”
Distinguish between concepts "chemical element" And “simple substance” possible by comparing the properties of simple and complex substances. For example, a simple substance - oxygen– a colorless gas necessary for breathing and supporting combustion. The smallest particle of the simple substance oxygen is a molecule that consists of two atoms. Oxygen is also included in carbon monoxide (carbon monoxide) and water. However, water and carbon monoxide contain chemically bound oxygen, which does not have the properties of a simple substance; in particular, it cannot be used for respiration. Fish, for example, do not breathe chemically bound oxygen, which is part of the water molecule, but free oxygen dissolved in it. Therefore, when we talk about the composition of any chemical compounds, it should be understood that these compounds do not include simple substances, but atoms certain type, that is, the corresponding elements.
When complex substances decompose, atoms can be released in a free state and combine to form simple substances. Simple substances consist of atoms of one element. The difference between the concepts of “chemical element” and “simple substance” is also confirmed by the fact that the same element can form several simple substances. For example, atoms of the element oxygen can form diatomic oxygen molecules and triatomic ozone molecules. Oxygen and ozone are completely different simple substances. This explains the fact that much more simple substances are known than chemical elements.
Using the concept of “chemical element”, we can give the following definition to simple and complex substances:
Simple substances are those that consist of atoms of one chemical element.
Complex substances are those that consist of atoms of different chemical elements.
The difference between the concepts of “mixture” and “chemical compound”
Complex substances are often called chemical compounds.
Try to answer the questions:
1.What is the difference in composition of the mixture from chemical compounds?
2. Compare the properties of mixtures and chemical compounds?
3. In what ways can you separate the components of a mixture and a chemical compound?
4. Is it possible to judge by external signs about the formation of a mixture and a chemical compound?
Comparative characteristics of mixtures and chemicals
|
Questions to match mixtures to chemical compounds |
Comparison |
|
|
Mixtures |
Chemical compounds |
|
|
How do mixtures differ in composition from chemical compounds? |
Substances can be mixed in any ratio, i.e. variable composition of mixtures |
The composition of chemical compounds is constant. |
|
Compare the properties of mixtures and chemical compounds? |
Substances in mixtures retain their properties |
Substances that form compounds do not retain their properties, since chemical compounds with other properties are formed |
|
In what ways can a mixture and a chemical compound be separated into its constituent components? |
Substances can be separated by physical means |
Chemical compounds can only be broken down through chemical reactions |
|
Is it possible to judge by external signs the formation of a mixture and a chemical compound? |
Mechanical mixing is not accompanied by the release of heat or other signs of chemical reactions |
The formation of a chemical compound can be judged by the signs of chemical reactions |
Tasks for consolidation
I. Work with simulators
II. Solve the problem
NaCl, H 2 SO 4, K, S 8, CO 2, O 3, H 3 PO 4, N 2, Fe.
Explain your choice in each case.
III. Answer the questions
№1
How many simple substances are written in a series of formulas:
H 2 O, N 2, O 3, HNO 3, P 2 O 5, S, Fe, CO 2, KOH.
№2
Both substances are complex:
A) C (coal) and S (sulfur);
B) CO 2 (carbon dioxide) and H 2 O (water);
B) Fe (iron) and CH 4 (methane);
D) H 2 SO 4 (sulfuric acid) and H 2 (hydrogen).
№3
Choose the correct statement:
Simple substances consist of atoms of the same type.
A) Correct
B) Incorrect
№4
What is typical for mixtures is that
A) They have a constant composition;
B) Substances in the “mixture” do not retain their individual properties;
C) Substances in “mixtures” can be separated by physical properties;
D) Substances in “mixtures” can be separated using a chemical reaction.
№5
The following are typical for “chemical compounds”:
A) Variable composition;
B) Substances contained in a “chemical compound” can be separated by physical means;
C) The formation of a chemical compound can be judged by the signs of chemical reactions;
D) Permanent composition.
№6
In what case are we talking about gland how about chemical element?
A) Iron is a metal that is attracted by a magnet;
B) Iron is part of rust;
C) Iron is characterized by a metallic luster;
D) Iron sulfide contains one iron atom.
№7
In what case are we talking about oxygen as a simple substance?
A) Oxygen is a gas that supports respiration and combustion;
B) Fish breathe oxygen dissolved in water;
C) The oxygen atom is part of the water molecule;
D) Oxygen is part of air.
In life we are surrounded by various bodies and objects. For example, indoors this is a window, door, table, light bulb, cup, outdoors - a car, traffic light, asphalt. Any body or object consists of matter. This article will discuss what a substance is.
What is chemistry?
Water is an essential solvent and stabilizer. It has strong heat capacity and thermal conductivity. The aqueous environment is favorable for the occurrence of basic chemical reactions. It is characterized by transparency and is practically resistant to compression.
What is the difference between inorganic and organic substances?
Particularly strong external differences There are no substances between these two groups. The main difference lies in the structure, where inorganic substances have a non-molecular structure, and organic substances have a molecular structure.
Inorganic substances have a non-molecular structure, therefore they are characterized high temperatures melting and boiling. They do not contain carbon. These include noble gases (neon, argon), metals (calcium, calcium, sodium), amphoteric substances (iron, aluminum) and nonmetals (silicon), hydroxides, binary compounds, salts.
Organic substances of molecular structure. They have enough low temperatures melting, and they quickly decompose when heated. Mainly composed of carbon. Exceptions: carbides, carbonates, carbon oxides and cyanides. Carbon allows the formation great amount complex compounds (more than 10 million of them are known in nature).
Most of their classes belong to biological origin (carbohydrates, proteins, lipids, nucleic acids). These compounds include nitrogen, hydrogen, oxygen, phosphorus and sulfur.
To understand what a substance is, it is necessary to imagine what role it plays in our lives. By interacting with other substances, it forms new ones. Without them, the life of the surrounding world is inseparable and unthinkable. All objects consist of certain substances, so they play an important role in our lives.
Nature develops dynamically, living and inert matter continuously undergoes processes of transformation. The most important transformations are those that affect the composition of a substance. The formation of rocks, chemical erosion, the birth of a planet, or the respiration of mammals are all observable processes that involve changes in other substances. Despite their differences, they all have something in common: changes at the molecular level.
- During chemical reactions, elements do not lose their identity. These reactions involve only the electrons in the outer shell of the atoms, while the nuclei of the atoms remain unchanged.
- The reactivity of an element to a chemical reaction depends on the oxidation state of the element. In ordinary chemical reactions, Ra and Ra 2+ behave completely differently.
- Different isotopes of an element have almost the same chemical reactivity.
- The rate of a chemical reaction is highly dependent on temperature and pressure.
- The chemical reaction can be reversed.
- Chemical reactions are accompanied by relatively small changes in energy.
Nuclear reactions
- During nuclear reactions, the nuclei of atoms undergo changes and, therefore, new elements are formed as a result.
- The reactivity of an element to a nuclear reaction is practically independent of the oxidation state of the element. For example, Ra or Ra 2+ ions in Ka C 2 behave in a similar way in nuclear reactions.
- In nuclear reactions, isotopes behave completely differently. For example, U-235 fissions quietly and easily, but U-238 does not.
- The rate of nuclear reaction does not depend on temperature and pressure.
- A nuclear reaction cannot be undone.
- Nuclear reactions are accompanied by large changes in energy.
Difference between chemical and nuclear energy
- Potential energy that can be converted into other forms, primarily heat and light, when bonds are formed.
- The stronger the bond, the greater the chemical energy converted.
- Nuclear energy does not involve the formation of chemical bonds (which are caused by the interaction of electrons)
- Can be converted into other forms when a change occurs in the nucleus of the atom.
Nuclear change occurs in all three main processes:
- Nuclear fission
- The joining of two nuclei to form a new kernel.
- Release of high energy electromagnetic radiation (gamma radiation), creating a more stable version of the same nucleus.
Energy conversion comparison
The amount of chemical energy released (or converted) in a chemical explosion is:
- 5kJ for every gram of TNT
- Amount of nuclear energy in a released atomic bomb: 100 million kJ for every gram of uranium or plutonium
One of the main differences between nuclear and chemical reactions has to do with how a reaction occurs in an atom. While a nuclear reaction occurs in the nucleus of an atom, the electrons in the atom are responsible for the chemical reaction that occurs.
Chemical reactions include:
- Transfers
- Losses
- Gain
- Electron sharing
According to the atomic theory, matter is explained by rearrangement to give new molecules. The substances involved in a chemical reaction and the proportions in which they are formed are expressed in the corresponding chemical equations underlying to perform various types chemical calculations.
Nuclear reactions are responsible for the decay of the nucleus and have nothing to do with electrons. When a nucleus decays, it can move on to another atom due to the loss of neutrons or protons. In a nuclear reaction, protons and neutrons interact within the nucleus. In chemical reactions, electrons react outside the nucleus.
The result of a nuclear reaction can be called any fission or fusion. A new element is formed due to the action of a proton or neutron. As a result of a chemical reaction, a substance changes into one or more substances due to the action of electrons. A new element is formed due to the action of a proton or neutron.
When comparing energy, a chemical reaction involves only a low energy change, whereas a nuclear reaction has a very high energy change. In a nuclear reaction, the energy changes are of magnitude 10^8 kJ. This is 10 - 10^3 kJ/mol in chemical reactions.
While some elements are transformed into others in the nuclear, the number of atoms remains unchanged in the chemical. In a nuclear reaction, isotopes react differently. But as a result of a chemical reaction, isotopes also react.
Although a nuclear reaction does not depend on chemical compounds, a chemical reaction is highly dependent on chemical compounds.
Summary
- A nuclear reaction occurs in the nucleus of an atom, the electrons in the atom are responsible for chemical compounds.
- Chemical reactions involve the transfer, loss, gain and sharing of electrons without involving the nucleus in the process. Nuclear reactions involve the decay of a nucleus and have nothing to do with electrons.
- In a nuclear reaction, protons and neutrons react inside the nucleus; in chemical reactions, electrons interact outside the nucleus.
- When comparing energies, a chemical reaction only uses a low energy change, whereas a nuclear reaction has a very high energy change.
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