The law of conservation of mass of substances in chemical reactions. The essence of a chemical reaction

The law of conservation of mass of substances is one of most important laws chemistry. It was discovered by M.V. Lomonosov, and later confirmed experimentally by A. Lavoisier. So what is the essence of this law?

Story

The law of conservation of mass of substances was first formulated by M.V. Lomonosov in 1748, and experimentally confirmed it using the example of firing metals in sealed vessels in 1756. Lomonosov connected the law of conservation of mass of substances with the law of conservation of energy (quantity of motion). He considered these laws in unity as universal law nature.

Rice. 1. M. V. Lomonosov.

But even before Lomonosov, more than 20 centuries ago, the ancient Greek scientist Democritus assumed that everything living and nonliving consists of invisible particles. later in the 17th century, these guesses were confirmed by R. Boyle. He conducted experiments with metal and wood and found that the weight of the metal increased after heating, and the weight of the ash, on the contrary, decreased compared to wood.

Regardless of M.V. Lomonosov, the law of conservation of mass of a substance was established in 1789 by the French chemist A. Lavoisier, who showed that in chemical reactions not only total mass substances, but also the mass of each of the elements that make up the interacting substances.

The views of Lomonosov and Lavoisier were confirmed modern science. In 1905, A. Einstein showed that there is a relationship between the mass of a body (m) and its energy (E), expressed by the equation:

where c is the speed of light in vacuum.

Rice. 2. Albert Einstein.

Thus, the law of conservation of mass provides a material basis for drawing up equations of chemical reactions.

The essence of the law of conservation of mass of matter

The law of conservation of mass of a substance is as follows: the mass of substances entering into a chemical reaction is equal to the mass of substances formed as a result of the reaction.

Rice. 3. Law of conservation of mass of matter.

When writing equations for chemical reactions, you must ensure compliance with this law. The number of atoms of an element in the left and right parts reactions should be the same, since atomic particles in chemical transformations they are indivisible and do not disappear anywhere, but only pass from one substance to another. Essence chemical reaction– breaking some bonds and forming other bonds. Since these processes are associated with the expenditure and production of energy, an equal sign in reactions can be put if energy factors, reaction conditions, states of aggregation substances.

Very often the equal sign, especially in inorganic reactions, put without taking into account the necessary factors, making a simplified recording. When equalizing coefficients, first they equalize the number of metal atoms, then non-metal, then hydrogen, and finally they check for oxygen.

What have we learned?

The law of conservation of mass of matter is studied at school in 8th grade chemistry, since understanding its essence is necessary for correct drafting reaction equations. The fact that any matter on earth consists of invisible particles was suggested by the ancient Greek scientist Democritus, and his more modern followers Lomonosov, Lavoisier, Einstein proved this experimentally.

Law of conservation of mass of substances. CHEMICAL EQUATIONS

Chemistry teacher, MAOU "Secondary School No. 12", Kungur Perm region Foteeva V.A.

TEST

Option 2

1 option

to the physical?

A) boiling water

A) freezing of water

B) decomposition of water by electric current

B) combustion of sulfur

B) juice fermentation

C) quenching soda with vinegar

D) melting of metals

D) melting paraffin

D) food burning

D) evaporation of the salt solution

E) water distillation

E) food burning

G) filtering

G) extinguishing soda with vinegar

H) making tea

H) yellowing of leaves

Examination

Option 2

1 option

Which of the following phenomena are to the physical?

Which of the following phenomena are chemical (chemical reactions)?

A) boiling water

B) combustion of sulfur

B) juice fermentation

D) melting paraffin

D) food burning

D) evaporation of the salt solution

G) filtering

G) extinguishing soda with vinegar

H) making tea

H) yellowing of leaves

Let's remember!!!

• What is a chemical reaction?
• What signs of chemical reactions do you know?
• What do you think happens to substances? quantitative changes, for example what happens to mass substances?
• What will be the opinions?
• Opinions are divided. Which one of you is right?

What will be the topic of the lesson?

(What happens to a mass of substances during chemical reactions?)

• How can we find out?
• (Carry out the experiment, read in the textbook).

EXPERIENCE:

V closed system The substances that enter into the reaction are weighed: solutions of barium chloride (BaCl 2) and magnesium sulfate (MgSO 4) - m1, as well as the substances formed as a result of the reaction: barium sulfate (BaSO 4) and magnesium chloride (MgCl2) - m2.

• What phenomenon did you observe? Why do you think so?
• What happened to the mass of substances before and after the reaction?
• What is the smallest particle of matter?
• What particles are molecules made of? Remember the definition ATOM.
• What does the chemical formula show?
• How is it calculated molar mass, mass of matter?
• So Why but m1=m2?
• Can you answer immediately this question? Why? What do you need to know?

(Maybe know chemical formulas- the composition of substances before and after the reaction and see changes whether atomic composition substances before and after the reaction?)

• What question arises?

(Does the atomic composition of substances change before and after the reaction?)

• What is the purpose of our lesson?

(Find out whether the quality and quantitative composition atoms in chemical reactions?)

Solving the problem

Let's write this reaction in Russian and then in chemical language:

barium chloride + magnesium sulfate barium sulfate + magnesium chloride

• 1atom Ba 1atom Mg 1atom Ba 1atom Mg
• 2 atoms Cl 1atom S 1atom S 2 atoms Cl
• 4 atoms O 4 atoms O

Before reaction After reaction

What conclusion can be drawn?

( Atoms and their composition before and after reaction have not changed )

• The results of weighing substances before and after the reaction confirm law conservation of mass substances. Students face a decision problematic task: why m1=m2? Thanks to the updating of previously acquired knowledge about the structure of substances, students relatively easily come to to the following conclusion: m1= m2, because atoms And their number as a result chemical transformations do not change, but only combine differently to form new substances.

Let's check our conclusion with calculations:

BaCl 2 + MgSO 4 Ba SO 4 + Mg Cl 2

Before the reaction - m1 After the reaction - m2

What did the calculations show?

What have you proven?

(m1= m2 ) Why?

Conservation Law

mass of matter

“All changes in nature that occur are of such a state that whatever is taken away from one body, the same amount is added to another. So, if matter decreases somewhere, it will increase in another place...”

Let's remember

Chemical formula – conventional recording of the composition of a substance using chemical symbols and indices.

Index shows the number of atoms in the formula unit of a substance.

Coefficient shows the number of particles not connected to each other

Chemical formula

Coefficient

Index

5H 2 ABOUT

Based on this law, equations are drawn up chemical reactions

by using chemical formulas, coefficients and

mathematical signs.

Reaction equation

X A + at IN = With AB

A, B, AB - chemical formulas

x, y, s - odds

PHOSPHORUS + OXYGEN = PHOSPHORUS(V) OXIDE

1.P+O 2 P 2 +5 O 5 -2

2 . Let's start with oxygen.

3. O - 2 atoms on the left O- 5 atoms on the right

4. NOC = 10

5. 10: 2 = 5 P+ 5 O 2 P 2 O 5

6. 10: 5 = 2 P+5O 2 2 P 2 O 5

7. B left side equations must be placed before the phosphorus formula

coefficient – 4

4 P+ 5 O 2 = 2 P 2 O 5

Do the exercises:

1. Arrange the coefficients in a chemical reaction

Al+O 2 Al 2 O 3

2.Write the chemical reaction using chemical formulas and arrange the coefficients

iron(III) hydroxide + nitric acid iron (III) nitrate + water

Independent work.

Level 1:

Find and fix errors:

Al + 3HCl ═ AlCl 3 + 3H 2

Level 2:

Arrange the coefficients in the chemical reaction diagram:

FeSO 4 + KOH → Fe(OH) 2 +K 2 SO 4

Level 3:

Write an equation for the chemical reaction and arrange the coefficients:

Phosphorus (V) oxide + sodium hydroxide → sodium phosphate + water

Answers

Level 1:

2 Al+ 6 HCl═ 2 AlCl 3 + 3 H 2

Level 2:

FeSO 4 + 2 KOH ═ Fe(OH) 2 +K 2 SO 4

Level 3:

P 2 O 5 + 6 NaOH ═ 2 Na 3 P.O. 4 + 3 H 2 O

Like Boyle, the Russian scientist experimented in sealed retorts. But, unlike Boyle, Lomonosov weighed the vessels both before and after calcination without opening them. m1=m2

After two hours of heating, the sealed tip of the retort was opened, and outside air burst into it noisily.

According to our observation, this operation resulted in a gain of 8 grains in weight...” m1 m2

TEST YOURSELF

1).M.V. Lomonosov discovered the law of conservation of mass of substances in:

A.1789 B.1756 B.1673

2). Establish the correct sequence of the law of conservation of mass of substances:

A - mass of substances

B - mass of substances

B- as a result of her

G-reacted,

D-resulting

E- equal

3). The conventional notation for a chemical reaction is: A. chemical formula B. coefficient

B. chemical equation D. index

REFLECTION

Choose the expression that matches your work in the lesson:

1. Patience and work will grind everything down.

2. Hard to learn - easy to fight.

3. A bad soldier is one who does not dream of becoming a general.

4. The only way leading to knowledge is activity.

5. Any knowledge has value only when it makes us more energetic.

Homework

pp.96-98 § 27, ex.1(b), 2(d),3(b)

Let's remember!!!

• What phenomena are called chemical?
• What conditions are necessary for a chemical reaction to occur?
• What signs indicate that a chemical reaction has occurred?
• How did we denote the composition of a substance?
• Can you indicate the reaction? What is the topic and purpose of our lesson?

Chemistry is the science of substances, their structure, properties and their transformation, resulting from chemical reactions, the foundation of which is laid chemical laws. All general chemistry rests on 4 basic laws, many of which were discovered by Russian scientists. But in this article we will talk about the law of conservation of mass of substances, which is part of the basic laws of chemistry.

Let us consider the law of conservation of mass of matter in detail. The article will describe the history of the discovery of the law, its essence and components.

Law of conservation of mass of matter (chemistry): formulation

The mass of substances entering into a chemical reaction is equal to the mass of substances formed as a result of it.

But let's get back to history. More than 20 centuries ago, the ancient Greek philosopher Democritus suggested that all matter is invisible particles. And only in the 17th century a chemist English origin put forward a theory: all matter is built from tiny particles substances. Boyle conducted experiments with metal by heating it over a fire. He weighed the vessels before and after heating and noticed that the weight increased. Burning wood had the opposite effect - the ash weighed less than the wood.

New story

The law of conservation of mass of substances (chemistry) was presented to the scientific association in 1748 by M.V. Lomonosov, and in 1756 it was attested experimentally. The Russian scientist provided evidence. If you heat hermetically sealed capsules with tin and weigh the capsules before heating, and then after, then the law of conservation of mass of a substance (chemistry) will be obvious. The formulation expressed by the scientist Lomonosov is very similar to the modern one. The Russian naturalist introduced undeniable contribution in the development of atomic-molecular science. He combined the law of conservation of mass of substances (chemistry) with the law of conservation of energy. Current teaching has confirmed these beliefs. And only thirty years later, in 1789, the natural scientist Lavoisier from France confirmed Lomonosov’s theory. But that was just a guess. It became law in the twentieth century (beginning), after 10 years of research by the German scientist G. Landolt.

Examples of experiments

Let's consider experiments that can confirm the law of conservation of mass of substances (chemistry). Examples:

1. We place red phosphorus in the vessel, cover it tightly with a stopper and weigh it. Heat over low heat. Education white smoke(phosphorus oxide) indicates that a chemical reaction has occurred. We weigh it again and make sure that the weight of the vessel with the resulting substance has not changed. Reaction equation: 4P+3O2 = 2P2O3.
2. We take two Landolt vessels. Into one of them, carefully so as not to mix, pour the reagents lead nitrate and potassium iodide. We also place ferric chloride in another vessel. Close the containers tightly. The scales must be balanced. Mix the contents of each vessel. In one, a yellow precipitate is formed - this is lead iodide, in the other, iron thiocyanate is obtained dark red. When new substances were formed, the scales maintained balance.
3. Let's light a candle and put it in a container. We seal this container hermetically. Bringing the scales into balance. When the air in the container runs out, the candle goes out and the reaction ends. The scales will be balanced, so the weight of the reactants and the weight of the substances formed are the same.
4. Let's conduct another experiment and consider the law of conservation of mass of substances (chemistry) as an example. The formula of calcium chloride is CaCl2, and that of sulfate acid is H2SO4. When these substances interact, a white precipitate is formed - calcium sulfate (CaSO4), and hydrochloric acid(HCl). For the experiment we will need scales and a Landolt vessel. Very carefully pour calcium chloride and sulfate acid into the vessel, without stirring them, and close them tightly with a stopper. We weigh on scales. Then we mix the reagents and observe that a white precipitate (calcium sulfate) precipitates. This shows that a chemical reaction has occurred. We weigh the vessel again. The weight remained the same. The equation for this reaction will look like this: CaCl2 + H2SO4 = CaSO4 + 2HCl.

Basics

The main goal of a chemical reaction is to destroy molecules in some substances and subsequently form new molecules of the substance. In this case, the number of atoms of each substance before and after the interaction remains unchanged. When new substances are formed, energy is released, and when they decay with its absorption, there is an energetic effect, manifested in the form of absorption or release of heat. During a chemical reaction, the molecules of the starting substances - the reactants - break down into atoms, from which the products of the chemical reaction are then obtained. The atoms themselves remain unchanged.

The reaction can last for centuries, or it can occur rapidly. When manufacturing chemical products, you need to know the speed of a particular chemical reaction, whether it absorbs or releases temperature, what pressure is needed, the amount of reagents and catalysts. Catalysts are small substances that do not participate in a chemical reaction, but significantly influence its speed.

How to write chemical equations

Knowing the law of conservation of mass of substances (chemistry), you can understand how to correctly compose chemical equations.

1. It is required to know the formulas of the reagents that enter into a chemical reaction and the formulas of the products that result from it.
2. On the left are the formulas of the reagents, between which there is a “+” sign, and on the right are the formulas of the resulting products with a “+” sign between them. An “=” sign or an arrow is placed between the formulas of the reagents and the resulting products.
3. The number of atoms of all components of the reactants must be equal to the number of atoms of the products. Therefore, coefficients are calculated and placed in front of the formulas.
4. It is forbidden to move formulas from the left side of the equation to the right or change their places.

Meaning of the law

The law of conservation of mass of substances (chemistry) made it possible most interesting subject develop as a science. Let's find out why.

• The great importance of the law of conservation of mass of substances in chemistry is that on its basis they do chemical calculations for industry. Suppose you need to obtain 9 kg of copper sulfide. We know that the reaction of copper and sulfur occurs in a mass ratio of 2:1. By this law, in a chemical reaction of copper weighing 1 kg and sulfur weighing 2 kg, copper sulfide weighing 3 kg is obtained. Since we need to obtain copper sulfide weighing 9 kg, that is, 3 times more, then we will need 3 times more reagents. That is, 6 kg of copper and 3 kg of sulfur.
• Ability to write correct chemical equations.

Conclusion

After reading this article, there should be no questions left regarding the essence of this law of the history of its discovery, to which, by the way, our famous compatriot, scientist M.V., is involved. Lomonosov. Which again confirms how great the power of Russian science is. The significance of the discovery of this law and its meaning also became clear. And those who did not understand, at school, after reading the article, should learn or remember how to do this.

Back Forward

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Lesson objectives:

1. Educational : systematize students’ knowledge about the classification of substances, teach students to compose equations of chemical reactions according to the Law of Conservation of Mass of Substances.

2. Developmental: improve students’ skills when composing chemical equations, develop their ability to compare and generalize, sustained attention; develop analytical thinking; carry out interdisciplinary communication.

3. Educational: to form an information and communication culture.

Equipment and reagents: scales, test tubes, flasks, HCL, CuSO 4, CaCO 3, H 2 SO 4, Cu(OH) 2.

Lesson type: combined.

Lesson plan:

1. Organizational moment.
2. Updating knowledge. (Crossword solution, dictation).
3. Learning new material:
   a) historical information;
   b) demonstration of experiments;
   c) the wording of the law;
   d) chemical equations.
4. Consolidation (Performing exercises).
5. Lesson summary.
6. Homework.
7. Song.

Greetings.

Lesson motto: “Oh, how many wonderful discoveries we have.”

The spirit prepares enlightenment..."

Today in the lesson we will talk about discoveries, learn a lot of new things, we will repeat the material we have covered, remember how formulas of substances are written, get acquainted with the law of conservation of mass of substances, learn to write equations. And to achieve our goals we will work according next plan: (a plan appears on the screen).

– Remember what phenomena exist in nature.

- How physical phenomena different from chemical ones?

– What is accompanied by chemical reactions?

– How are substances designated in chemistry?

– Who suggested this designation?

Now, pay attention to the screen. You see a crossword puzzle, by solving which you will not only repeat what everyone knows, but also learn the topic of our lesson today.

Please note that the title is written and the keyword is in red and encrypted. After solving, the correct answers appear on the screen.

Well done! Thus, the topic of our lesson is: “ Chemical equations.

Law of conservation of mass of substances”

We open the notebooks, write the date and topic of the lesson.

Now we will write a dictation.

I will name the substances, and you will write down the formulas.

Ba(NO 3), BaCL 2, HCL, Cu SO 4, CaC O 3, H 2 O, NaOH, H 2 SO 4, HNO 3, AL 2 O 3,

Zn (NO 3) 2, Mg CL 2.

appear on the screen correct formulas. Students check their notes.

Now that we have remembered the signs and formulas, we will begin to study new material.

Historical background

Z.S.M.V. was discovered by the great Russian scientist Lomonosov in 1748, later confirmed this law in 1789 French chemist Lavoisier. What is the story of the discovery?

Lomonosov's inquisitive mind was occupied by the thought of what happens to substances that enter into a chemical reaction.

Does their composition and mass change?

He conducted experiments.

At first, he took vessels with open holes for experiments. The mass changed.

Then he conducted experiments in sealed glass retorts - the mass remained unchanged.

Then he explained the law by saying that During chemical reactions, atoms do not disappear or appear, but only their rearrangement occurs..

Now we will conduct experiments that confirm Lomonosov’s discoveries.

Demonstration of experiments:

What conclusion can we draw about how the mass of substances has changed?

What law of physics has such a semantic meaning? (law of conservation of energy).

How is it formulated?

In all phenomena occurring in nature, energy neither appears nor disappears. It only transforms from one type to another, while its meaning remains the same.

– Now that you have remembered the law of conservation of energy and learned the essence of the law of conservation of mass of substances. try to formulate the Law of Conservation of Mass of Substances itself. (The law appears on the screen)

- Write it down in your notebook.

The mass of substances that entered into a chemical reaction is equal to the mass of substances formed as a result of the reaction.

– Substances react and new substances are formed.

We talk about all this. How can this be written down?

And these processes are written using equations.

Just as in Russian you make words from letters, and from words into sentences, so in chemistry you make formulas from signs, and equations from formulas.

The following symbols are used to write equations in chemistry:

When writing equations, you need to adhere to the following algorithm of actions (on the screen).

N 2 +H 2. -> NH 3
N 2 +3 H 2 -> 2NH 3

- Guys, who can guess what a chemical equation is?

(The wording appears on the screen)

– A chemical equation is a conventional representation of a chemical reaction using chemical formulas.

Substances taking part in the reaction are called reagents.

Substances formed as a result of the reaction - products reactions.

Students write in their notebooks.

– Now let’s create an equation for the reaction we carried out.

2HCL+ CuSO 4 ->CuCL 2 + H 2. SO 4
2HCL+ CaCO 3 ->Ca CL 2 + H 2 CO 3
Cu(OH) 2 + H 2 SO 4 ->Cu SO 4 + H 2 O

- Guys, who has any questions?

– And now we will perform several exercises to consolidate:

1. What coefficient is in the reaction equation before the formula of hydrochloric acid

2. Continue the reaction equations, arrange the coefficients:

AL + O 2 -> … (AL 2 O 3)

3. Write down the reaction equations and arrange the coefficients: sodium sulfate combines with barium nitrate to form barium sulfate and sodium nitrate

(Na 2 SO 4 +Ba (N O 3) 2 -> Ba S O 4 v+ 2NaN O 3)

3. Find errors:

5.Complete the equations:

6. Perform a series of transformations, write down the reaction equations:

Ca -> CaO -> (CaOH) 2

- We're done, okay. Pay attention to the screen. Take each other's notebooks and test yourself. Change back. Who has everything right? Fine.

– What conclusions can we draw?

– What are we going through in class?

– How are the equations equalized?

– Who discovered the Law of Conservation of Mass of Substances?

-What is an equation called?

– What are the names of the substances that reacted?

– What are the names of the resulting substances?

Great job today
Can I let you down result.
You all tried, you weren’t lazy
And everyone did as much as they could!
Grading.

– Now, write in your diaries:

D om.task .

P. 31, exercises 2, 3. p. 110, for inquisitive exercises. 2,3,4.

- Fine!

– And we will end the lesson with a song about the Law based on the song “ Smile”.

Lomonosov discovered this law
Confirmed by the French chemist Lavoisier
Masses of all substances that reacted
Equal to the mass of the resulting substances
Every atom is not a fool
It does exactly this:
Will not appear, will not disappear
Won't change

Well, the mass is as always
There is only one of these atoms
And in starting materials she won't change. – 2 times

Lomonosov's law then
In chemistry it has become the main panacea
All reactions are now always
Compiled by a system of equations.

Every atom is not a fool
It does exactly this:
Will not appear, will not disappear
Won't change

Well, the mass is as always
There is only one of these atoms
And it will not change in the original substances. - 2 times

Lesson topic: Law of conservation of mass of substances. Chemical equations

Educational objectives:

Review concepts about physical and chemical phenomena, chemical reactions and their essence;

Based on demonstration experiment lead students to the discovery of the law of conservation of mass of substances;

Using a video fragment of the electronic application to the textbook, introduce students to historical information discovery of the law of conservation of mass of substances;

Show the significance of the discovery of the law in chemistry and for production;

Developmental tasks:

Promote the development of independent and group work skills;

Promote development cognitive activity students in the classroom through the use of video clips from an electronic application;

Develop logical thinking students to be able to explain the results of a demonstration experiment;

Develop the ability to apply the law of conservation of mass of substances to solve problems and draw up reaction equations.

Educational tasks:

Continue to instill accuracy in students in writing down notes when solving problems and writing reaction equations;

To help students develop the ability to listen to the opinions of others, to various forms oral presentations, evaluation different points vision.

Foster a culture of mental work, a dialectical-materialistic perception of the world.

Lesson type: A lesson in learning new knowledge.

Forms and methods: story, conversation, independent work, work with a textbook, visual, work in groups.

Equipment: laptop, multimedia projector, interactive whiteboard, electronic application, PSHE, scales, a device for demonstrating the law of conservation of mass of substances.

Reagents: Solutions of sodium sulfate and barium chloride.

Demos: 1) interaction of barium chloride and sodium sulfate on the scales; 2) video fragments of the electronic supplement to the textbook.

Expected result:

Student:

defines the law of conservation of mass of substances, knows its essence;

arranges coefficients in equations of chemical reactions;

calculates the mass of a substance (product or reactant) using the law of conservation of mass of substances.

PROGRESS OF THE LESSON

I. Organizing students for the lesson.

II. Update background knowledge. Motivation educational activities. Statement of a problematic question.

1. Frontal survey

"GAME - exercise." The teacher lists physical and chemical phenomena. Students listen carefully. If a chemical phenomenon is named, they raise their hand up. The student who answered incorrectly gives a definition of a physical or chemical phenomenon and additionally gives his own example:

a) souring of milk;

b) grape fermentation;

c) melting ice;

d) rusting of a nail;

e) melting paraffin;

f) evaporation of alcohol;

g) boiling distilled water;

h) combustion natural gas;

i) frost formation;

j) rotting garbage.

2. Conversation

Teacher: Remember the experiment on sulfur combustion when studying the topic “Physical and Chemical Phenomena”. How did we write down the scheme for this chemical reaction? (the student writes down a chemical reaction diagram on the board using the chemical formulas S + O 2 SO 2, at this time with the class we frontally check the mechanism for writing a chemical reaction diagram, which was worked out in that lesson).

What are the names of the starting and final substances in a reaction scheme?

What happens to the sulfur and oxygen atoms after the end of a chemical reaction, judging by its diagram?

3. Determining the topic and purpose of the lesson, its significance in chemical science.

Teacher: Today in the lesson we are faced with an extremely responsible mission - to discover for ourselves one of the most important laws of nature and science. You will try yourself in the role of theoreticians and partly practitioners, solving simple exercises and problems.

In a few minutes you will independently formulate the topic of today's lesson.

The motto of our lesson will be the words of the English philosopher F. Bacon: “Truth is the daughter of time, not authority”. Be careful, because at the end of the lesson I will ask you to explain what the author meant by this statement. You also have to answer key question: “How do chemists understand the world of substances?”

Conversation

Teacher: Let's return again to the scheme of the chemical combustion reaction we know simple substance sulfur. What do you think: What is the essence of a chemical reaction? (Sulfur and Oxygen atoms do not disappear, and new atoms do not appear, but they are rearranged, resulting in the formation of a new substance es-O-two). So, the essence of the chemical reaction is rearrangement of atoms of elements resulting in the formation of new substances.

Teacher: Does the number of atoms change before and after the reaction? (the number of atoms of the elements does not change).

Teacher:Does the mass of Sulfur and Oxygen atoms change before and after the reaction?(the mass of atoms of the elements Sulfur and Oxygen does not change).

Teacher: So, does the total mass of substances change before and after the reaction?

(the mass of substances before and after the reaction does not change).

Teacher's story

This is our theoretical assumption, which in science is called Hypothesis. Hypothesis is a thought, an assumption that requires proof. When a hypothesis is confirmed practically, experimentally, then it becomes by law.

Determine the topic of our lesson(students formulate the topic of the lesson)

III. Learning new material.

1. The history of the discovery of the law.

Story accompanied by video clips

Teacher: In 1676, the English physicist and chemist Robert Boyle conducted the following experiment: he weighed a sealed retort with metal powder, long time heated it, then cooled it to room temperature, opened the retort and weighed it again. The weight of the retort with its contents increased. On the basis of which R. Boyle concludes that the mass of calcined metal increases due to the combination of the metal with “fiery force”, which penetrates through the walls of the retort ( video clip 1). Such particles of “fiery force” were called at that time phlogistons. There was even a whole theory of phlogiston.

However, according to our theoretical reasoning The mass of substances before and after the reaction must remain unchanged!

SO WHO IS WRONG? Us or R. Boyle? What can we do? Right! Conduct your own experiment!

Demonstration. Before carrying out the experiment, we will balance the Landol vessel (a double-ended test tube) on technical scales. Pour a colorless barium chloride solution into one elbow, and a colorless sodium sulfate solution into the other. Having tilted the test tube, we pour the contents of one elbow to the contents of the other, i.e. mix transparent substances. We observe the formation of a white precipitate.

Teacher: What does it indicate? this sign reactions?

(about the formation of a new substance).

Observation: The balance of the scales is not disturbed!

Conclusion:We're right! This is already a LAW.

Teacher:What mistake did R. Boyle make?(students' answers).

Teacher: I congratulate you all, we have discovered one of the most important laws of nature about the conservation of the mass of matter during chemical reactions.

However, before us it was discovered by a scientist with multifaceted talent, who also had doubts about the validity of the experiments

R. Boyle ( video clip 2).

Teacher: How M.V. Did Lomonosov change the experience? He conducted a series of experiments similar to those carried out by R. Boyle with the calcination of metals in retorts. He noticed that if a vessel containing metal is weighed before and after calcination, without opening it, then the mass remains unchanged. Experiments by M.V. Lomonosov is refuted by the experiments and conclusions of R. Boyle.

Lomonosov calls his law the Law of Conservation of Mass of Substances. The fact that atoms have constant mass, and determines the conservation of the mass of the substance. Lomonosov wrote: “All changes in Nature that occur are of such a state that as much of something is taken away from one body, the same amount is added to another. So, if matter decreases somewhere, it will increase in another place...”

This discovery was a huge breakthrough in science, an impetus for its development, since R. Boyle’s assumption dominated chemistry for almost a century and thereby held back its development. We came to the essence of the law simply... but in science, discoveries do not happen quite simply. The lack of precise instruments, knowledge about gases, and the inability to weigh them did not make it possible to discover this law of nature.

2. Discovery of A.L. Lavoisier.

Lavoisier wrote: “Mass is never formed or disappears, but only passes from one substance to another.” “Elements do not appear or disappear, but only their rearrangement.”

Teacher: Do you know any facts that are an exception to this law? For example: after burning firewood, its mass clearly decreases compared to the original one. Is this true? Explain your answer (students' answers). No!

Corollary of the law:“Nothing comes from nothing and disappears without a trace. Science does not know of a single case in which this law was violated during any process.”

3. Application of the law of conservation of mass of substances, its significance.

in chemical production;

when drawing up chemical equations of reactions;

in calculations when solving problems;

The discovery of the law of conservation of mass of substances contributed to the further development of chemical science and understanding of the laws of nature.

Teacher: I propose to test the law in action using the example of the well-known reaction of sulfur combustion and hydrogen combustion.

S + O 2 = SO 2

32 32 64 The law is in effect!

H 2 + O 2 = H 2 O

2 + 32 = 18The law does not apply!

Teacher: Since atoms do not disappear and new ones are not formed, their number, according to the law of conservation of mass, must be equal. How can this be achieved? This can be achieved by selecting coefficients.

2 H 2 + O 2 = 2 H 2 O

4 + 32 = 36 The law works!

Teacher: The law of conservation of mass of substances is also applied to solve problems. For example: What mass of sulfur must be burned in 4 g of oxygen to obtain 8 g of sulfur(IV) oxide?

Given: Solution:

m(O 2) = 4 g m(S) + m(O 2) = m(SO 2)

m(S) – ? m(S) = m(SO 2) – m(O 2) = 8 g – 4 g = 4 g

Answer: m(S) = 4 g

IV. Consolidation of acquired knowledge.

Work in pairs

1. Arrange the coefficients in the equations of chemical reactions:

a) Na + С1 2 → NaС1; b) Ag + S → Ag 2 S;

d) HgO → Hg + O 2; e) Na + O 2 → Na 2 O.

2. Solve problems:

a) When burning 24 kg of coal, 88 kg were formed carbon dioxide. What mass of oxygen is required for this?

b) What mass of mercury can be obtained by decomposition of 8.68 g of mercury(II) oxide, if 0.64 g of oxygen is released?

Independent work

1. Complete the sentences:

a) The law of conservation of mass of substances was experimentally confirmed by: _____________________________ and ______________________________.

b) Modern formulation The law of conservation of mass of substances is: ___________________________________________________________________.

c) The law of conservation of mass of substances is used to compose _____________________________ and _______________________________.

d) The number of atoms before the reaction must always be equal to _______________________________________________________________.

e) The coefficient is always set to ________________________________.

2. The sum of all coefficients in the equation of a chemical reaction

P + O 2 = P 2 O 5, equal to:

a) 8; b) 9; c) 11; d) 6.

V. Generalization and systematization of acquired knowledge.

Frontal survey

What topic did we study in class today?

Who discovered the law of conservation of mass of substances?

What is the significance of the law of conservation of mass of substances and where is it applied?

What consequence follows from the law of conservation of mass of substances?

What is the essence of a chemical reaction?

What is a coefficient called and why is it used in equations of chemical reactions?

VI. Reflection.

So, what meaning do you think F. Bacon put into the expression: “Truth is the daughter of time, not authority”?

How do chemists understand the world of substances?

Today in class...

found out... understood... liked...

Learned... will help... interesting...

VII. Instruction D/z.

§ 20, pp. 67 – 68, ex. 3, 4, 5, test tasks 1 , 2 .

Use the textbook's electronic supplement to prepare for the lesson.

VIII. Summing up the lesson.