Reaction Equations in Chemistry 8. How to balance chemical equations

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The purpose of the lesson: to help students form knowledge about a chemical equation as a conditional record of a chemical reaction using chemical formulas.

Tasks:

Educational:

• systematize previously studied material;
• to teach the ability to write equations of chemical reactions.

Educational:

• develop communication skills (work in pairs, the ability to listen and hear).

Developing:

• develop educational and organizational skills aimed at fulfilling the task;
• develop analytical thinking skills.

Lesson type: combined.

Equipment: computer, multimedia projector, screen, evaluation sheets, reflection card, “set of chemical symbols”, notebook with printed base, reagents: sodium hydroxide, iron(III) chloride, spirit lamp, holder, matches, drawing paper sheet, multi-colored chemical symbols.

Lesson presentation (Appendix 3)

Lesson structure.

I. Organizing time.
II. Updating knowledge and skills.
III. Motivation and goal setting.
IV. Learning new material:
4.1 combustion reaction of aluminum in oxygen;
4.2 decomposition reaction of iron (III) hydroxide;
4.3 algorithm for placing coefficients;
4.4 minute of relaxation;
4.5 arrange the coefficients;
V. Consolidation of acquired knowledge.
VI. Summing up the lesson and grading.
VII. Homework.
VIII. Final word from the teacher.

During the classes

The chemical nature of a complex particle
determined by the nature of the elementary
components,
their number and
chemical structure.
D.I. Mendeleev

Teacher. Hello guys. Sit down.
Please note: there is a notebook with a printed basis on your table (Appendix 2), in which you will work today, and an evaluation sheet, in which you will record your achievements, sign it.

Teacher. We got acquainted with physical and chemical phenomena, chemical reactions and signs of their occurrence. We studied the law of conservation of mass of substances.
Let's test your knowledge. I suggest that you open your notebooks with a printed base and complete task 1. You are given 5 minutes to complete the task.

1. How do chemical reactions differ from physical phenomena?

1. Change in the form, state of aggregation of matter.
2. The formation of new substances.
3. Location change.

2. What are the signs of a chemical reaction?

3. In accordance with what law are the equations of chemical reactions compiled?

1. The law of the constancy of the composition of matter.
2. The law of conservation of mass of matter.
3. Periodic law.
4. The law of dynamics.
5. The law of universal gravitation.

4. The law of conservation of mass of matter discovered:

1. DI. Mendeleev.
2. C. Darwin.
3. M.V. Lomonosov.
4. I. Newton.
5. A.I. Butlerov.

5. The chemical equation is called:

Teacher. You've done the job. I suggest you check it out. Swap notebooks and check each other. Attention to the screen. For each correct answer - 1 point. Record the total score on the score sheet.

Teacher. Using this knowledge, today we will compose the equations of chemical reactions, revealing the problem “Is the law of conservation of mass of substances the basis for compiling the equations of chemical reactions”

Teacher. We are used to thinking that an equation is a mathematical example where there is an unknown, and this unknown needs to be calculated. But in chemical equations, there is usually nothing unknown: everything is simply written in them with formulas: what substances enter into the reaction and what are obtained during this reaction. Let's see the experience.

(The reaction of sulfur and iron compounds.) Appendix 3

Teacher. From the point of view of the mass of substances, the reaction equation for the combination of iron and sulfur is understood as follows

Iron + sulfur → iron (II) sulfide (task 2 tpo)

But in chemistry words are reflected by chemical signs. Write this equation in chemical symbols.

Fe + S → FeS

(One student writes on the blackboard, the rest in the TVET.)

Teacher. Now read.
Learners. An iron molecule interacts with a sulfur molecule, one molecule of iron (II) sulfide is obtained.
Teacher. In this reaction, we see that the amount of starting materials is equal to the amount of substances in the reaction product.
It must always be remembered that when drawing up reaction equations, not a single atom should be lost or unexpectedly appear. Therefore, sometimes, having written all the formulas in the reaction equation, you have to equalize the number of atoms in each part of the equation - to arrange the coefficients. Let's see another experience

(Combustion of aluminum in oxygen.) Appendix 4

Teacher. Let's write the chemical reaction equation (task 3 in TPO)

Al + O 2 → Al +3 O -2

To write down the formula of the oxide correctly, remember that

Learners. Oxygen in oxides has an oxidation state of -2, aluminum is a chemical element with a constant oxidation state of +3. LCM = 6

Al + O 2 → Al 2 O 3

Teacher. We see that 1 aluminum atom enters the reaction, two aluminum atoms are formed. Two oxygen atoms enter, three oxygen atoms are formed.
Simple and beautiful, but disrespectful to the law of conservation of mass of substances - it is different before and after the reaction.
Therefore, we need to arrange the coefficients in this chemical reaction equation. To do this, we find the LCM for oxygen.

Learners. LCM = 6

Teacher. Before the formulas for oxygen and aluminum oxide, we set coefficients so that the number of oxygen atoms on the left and right is 6.

Al + 3 O 2 → 2 Al 2 O 3

Teacher. Now we get that as a result of the reaction four aluminum atoms are formed. Therefore, before the aluminum atom on the left side we put the coefficient 4

Once again, we count all the atoms before and after the reaction. We put it equal.

4Al + 3O 2 _ = 2 Al 2 O 3

Teacher. Consider another example

(The teacher demonstrates an experiment on the decomposition of iron (III) hydroxide.)

Fe(OH) 3 → Fe 2 O 3 + H 2 O

Teacher. Let's set up the coefficients. 1 iron atom enters the reaction, two iron atoms are formed. Therefore, before the formula of iron hydroxide (3) we put the coefficient 2.

Teacher. We get that 6 hydrogen atoms (2x3) enter into the reaction, 2 hydrogen atoms are formed.

Learners. LCM =6. 6/2 \u003d 3. Therefore, we set the coefficient 3 for the water formula

2Fe(OH) 3 → Fe 2 O 3 + 3 H 2 O

Teacher. We count oxygen.

Learners. Left - 2x3 = 6; right – 3+3 = 6

Learners. The number of oxygen atoms involved in the reaction is equal to the number of oxygen atoms formed during the reaction. You can set equal.

2Fe(OH) 3 = Fe 2 O 3 +3 H 2 O

Teacher. Now let's summarize everything that was said earlier and get acquainted with the algorithm for arranging the coefficients in the equations of chemical reactions.

Teacher. You've worked hard and you're probably tired. I suggest you relax, close your eyes and remember some pleasant moments of life. Each of you is different. Now open your eyes and make circular movements with them, first clockwise, then counterclockwise. Now intensively move your eyes horizontally: right - left, and vertically: up - down.
And now we will activate mental activity and massage the earlobes.

Teacher. We continue to work.
In notebooks with a printed base, we will complete task 5. You will work in pairs. You need to place the coefficients in the equations of chemical reactions. You have 10 minutes to complete the task.

• P + Cl 2 →PCl 5
• Na + S → Na 2 S
• HCl + Mg → MgCl 2 + H 2
• N 2 + H 2 → NH 3
• H 2 O → H 2 + O 2

Teacher. Let's check the execution of the task ( the teacher asks and displays the correct answers on the slide). For each correctly set coefficient - 1 point.
You have completed the task. Well done!

Teacher. Now let's get back to our problem.
Guys, what do you think, is the law of conservation of mass of substances the basis for compiling equations of chemical reactions.

Learners. Yes, during the lesson we proved that the law of conservation of mass of substances is the basis for compiling equations of chemical reactions.

Teacher. We have covered all the key issues. Now let's do a little test to see how well you've mastered the topic. You must answer it only “yes” or “no”. You have 3 minutes to work.

Statements.

1. In the reaction Ca + Cl 2 → CaCl 2 coefficients are not needed.(Yes)
2. In the reaction Zn + HCl → ZnCl 2 + H 2, the coefficient of zinc is 2. (No)
3. In the reaction Ca + O 2 → CaO, the coefficient of calcium oxide is 2.(Yes)
4. In the CH 4 → C + H 2 reaction, the coefficients are not needed.(No)
5. In the reaction CuO + H 2 → Cu + H 2 O, the coefficient for copper is 2. (No)
6. In the reaction C + O 2 → CO, the coefficient 2 must be set for both carbon monoxide (II) and carbon. (Yes)
7. In the reaction CuCl 2 + Fe → Cu + FeCl 2, the coefficients are not needed.(Yes)

Teacher. Let's check the work. For each correct answer - 1 point.

Teacher. You did a good job. Now calculate the total number of points scored for the lesson and rate yourself according to the rating that you see on the screen. Give me the score sheets to put your grade in the journal.

Teacher. Our lesson came to an end, during which we were able to prove that the law of conservation of mass of substances is the basis for compiling reaction equations, and learned how to write chemical reaction equations. And, as a final point, write down your homework

§ 27, ex. 1 - for those who received a rating of "3"
ex. 2 - for those who received a rating of "4"
ex. 3 - for those who received a rating“5”

Teacher. I thank you for the lesson. But before you leave the office, pay attention to the table (the teacher points to a sheet of drawing paper with a table and multi-colored chemical signs). You see chemical signs in different colors. Each color symbolizes your mood. To do this, you must go to the music sheet, take one chemical element, according to the characteristic that you see on the screen, and attach it to the cell of the table. I will do it first, showing you my comfort from working with you.

Instruction

Task. Calculate the mass of aluminum sulfide if 2.7 g of aluminum reacted with sulfuric acid.

Write down a short condition

m(Al2 (SO4) 3)-?

Before tasks on , we compose a chemical equation. With a dilute acid, a salt is formed and a gaseous substance, hydrogen, is released. We set the coefficients.

2Al + 3H2SO4 = Al2 (SO4) 3 + 3H2

When solving, one should always pay attention only to substances for which the parameters are known, and it is also necessary to find. All others are not taken into account. In this case, these will be: Al and Al2 (SO4) 3

We find the relative molecular weights of these substances according to the table of D.I. Mendeleev

Mr(Al2 (SO4) 3) =27 2(32 3+16 4 3) =342

We translate these values ​​into molar masses (M), multiplying by 1 g / mol

M(Al) =27g/mol

M (Al2 (SO4) 3) \u003d 342 g / mol

We write down the basic formula that relates the amount of substance (n), mass (m) and molar mass (M).

We carry out calculations according to the formula

n(Al) \u003d 2.7g / 27g / mol \u003d 0.1 mol

We make two ratios. The first ratio is compiled according to the equation on the basis of the coefficients in front of the formulas of substances, the parameters of which are given or need to be found.

First ratio: 2 mol of Al accounts for 1 mol of Al2 (SO4) 3

The second ratio: 0.1 mol of Al accounts for X mol of Al2 (SO4) 3

(compiled based on the calculations obtained)

We solve the proportion, given that X is the amount of substance

Al2 (SO4) 3 and has the unit mol

n (Al2 (SO4) 3) \u003d 0.1 mol (Al) 1 mol (Al2 (SO4) 3): 2 mol Al \u003d 0.05 mol

Now we have the amount of substance and the molar mass of Al2(SO4)3, therefore, we can find the mass, which we derive from the main formula

m (Al2 (SO4) 3) \u003d 0.05 mol 342 g / mol \u003d 17.1 g

We write down

Answer: m (Al2 (SO4) 3) \u003d 17.1 g

At first glance, it seems that solving problems in chemistry is very difficult, but it is not. And to check the degree of assimilation, for this, first try to solve the same problem, but only on your own. Then plug in the other values ​​using the same equation. And the last, final stage will be the solution of the problem according to the new equation. And if you managed to cope, well - you can be congratulated!

Related videos

Helpful advice

A wonderful assistant in solving problems is the time-tested manual "Problems in Chemistry for applicants to universities" by G.P. Khomchenko. And do not be afraid to use it - it offers a solution to problems from the very beginning!

Sources:

• solve a chemistry problem

The school curriculum is quite rich, theoretical knowledge is acquired, but there are no practical skills for solving. What to do and how to learn to solve problems in chemistry? What is the first thing you need from a student?

Solving problems in chemistry has its own specifics, and you need to find a starting point that will help you learn how to understand this difficult matter.

What you need to know to solve problems in chemistry

In order to correctly solve problems in chemistry, you first need to know the valency of the elements. The compilation of the formula of a substance depends on this; the equation of a chemical reaction cannot be compiled or equalized without taking into account the valency. The periodic table is used in almost every task, you need to learn how to use it correctly in order to get the necessary information about chemical elements, their mass, electronic. Most often, in tasks it is required to calculate the mass or volume of the resulting product, this is the basis.

If the valence is determined incorrectly, all calculations will be incorrect.

And then other, more complex tasks will be solved more easily. But first of all - the formulas of substances and correctly drawn up equations of ongoing reactions, indicating what will eventually turn out, and in what form. It can be a liquid, a free-flowing gas, a solid that precipitates or is dissolved in water or other liquid.

Where to start when solving problems in chemistry

To solve the problem, its condition is briefly written. After that, the reaction equation is drawn up. For example, we can consider specific data: you need to determine the mass of the substance obtained, aluminum sulfide, during the reaction of aluminum metal with sulfuric acid, if 2.7 grams of aluminum is taken. You should pay attention only to the substances that are known, after that - to those that you want to find.

You need to start deciding by converting the mass in grams to molar. Write a formula for the reaction, substitute the mass values ​​​​into it and calculate the proportion. After a simple task has been solved, you can try to master a similar one yourself, but with other elements, as they say, to fill your hand. The formulas will be the same, only the elements will change. The whole solution of problems in chemistry comes down to writing the correct formula of a substance, then to the correct compilation of the reaction equation.

All tasks are solved according to the same principle, the main thing is to correctly place the coefficients in the equation.

Sources:

• How to solve problems in chemistry

Topic: Chemical Equations

Target: repeat and expand knowledge of chemical reactions; to form the concept of a chemical equation as a conditional representation of a chemical reaction; explain the rules for compiling equations of chemical reactions, selecting coefficients based on the law of conservation of the mass of a substance; stimulate the cognitive activity of students through didactic games, set them up to use existing knowledge to learn new material.

Motivation: What are chemical equations and why are they needed?

Equipment and reagents: Periodic Table of Chemical Elements

D. I. Mendeleev; cards.

Lesson type: assimilation of new knowledge

Conduct forms: chemical warm-up, work in pairs, work with a textbook,

independent work.

During the classes

Organizational stage

Preparing the class for the lesson.

Updating of basic knowledge

Warm up

Blitz Poll:

1. What does chemistry study? (Substance.)

2. What is a substance? (This is a certain type of matter, what the body consists of).

3. How do we express the composition of matter? (Using chemical formulas).

4. How to make a chemical formula? What do you need to know for this?

(Chemical signs of elements, valency.)

Guess the chemical element (work with cards)

H, O, S, Fe, Cu, Al, Na, Cl.

Planned response:

The name of the chemical element

Name of a simple substance

Valence,

Relative atomic mass

Tic-tac-toe game

Winning Path - Simple Substances

Which substances are called simple, which are complex?

Winning Path - Chemical Phenomena

burning coal

nail rusting

glass melting

Which phenomena are called physical, which are chemical?

List signs of chemical reactions.

Work with text:

"When hydrogen H 2 and oxygen O 2 interact, water H 2 O is formed"

“During the combustion (interaction with oxygen O 2) of coal C, carbon dioxide CO 2 is formed”

What phenomenon are we talking about? How to write this chemical reaction?

Problem: How to write a chemical reaction?

What is a chemical equation?

Motivation:

What do you know about the equation in general?

In what subjects did you meet with equations?

An equation is a mathematical equation with one or more unknowns.

What do you think a chemical equation is?

We return to our texts.

How can you express (write down) a chemical reaction?

What law should be applied when compiling chemical equations? What does he say?

Learning new material

Drawing up equations of chemical reactions of interaction of simple substances

The principle of compiling equations of reactions for obtaining binary compounds from simple substances:

on the left side of the equation, those simple substances should be present, the atoms of the elements of which are present in the compound on the right side of the equation. So, to obtain water, it is necessary that hydrogen and oxygen react with each other.

We write the reaction equation and arrange the coefficients:

H 2 + O 2  H2O.

Indicate the reactants and products of the chemical reaction in the equation.

What are reagents?

What are reaction products?

In general algorithm for compiling a chemical equation has this look. 66 textbooks:

1. Draw up an interaction diagram: write down the formulas of the reagents on the left, putting a “+” sign between them. On the right, write down the formulas for the reaction products. If there are several of them, also put a “+” sign between them. Between the left and right parts of the diagram, put the sign "  ».

2. Select the coefficients for the formulas of each of the substances so that the number of atoms of each element on the left side is equal to the number of atoms of this element on the right side of the diagram.

3. Compare the number of atoms of each element in the left and right parts of the diagram. If they are the same, replace the "  » sign « = ».

According to chemical equations, the masses of reactants and reaction products are calculated.

So: let's formulate the definition of the chemical equation:

A chemical equation is a conditional record of a chemical reaction using chemical formulas, mathematical signs and coefficients.

The equations of chemical reactions are based on the law of conservation of mass of substances.

The coefficients in the chemical equation show the simplest relationships between the amounts of structural particles of reactants and reaction products.

The number of atoms of each element on the left and right sides of the equation is the same.

Consolidation and generalization of knowledge

“Heated iron powder was introduced into a flask with a yellow-green gas - chlorine, the molecules of which are diatomic. The powder ignited, resulting in brown smoke formed by particles of iron (III) chloride. Write down the reaction equation.

2. Select coefficients for the following reactions:

a) Fe + Cl 2  FeCl 3 ;

b) Na + Br 2  NaBr;

c) P + O 2  R 2 O 3 ;

d) KS1O 3  KC1 + O 2;

e) FeCl 2 + C1 2  FeCl 3 ;

f) FeCl 3 + Br 2  FeBr 3 + C1 2

3. Write down the interaction equations for the following simple substances and arrange the coefficients:

a) hydrogen and sulfur;

b) magnesium and oxygen;

c) aluminum and oxygen;

d) aluminum and sulfur;

e) zinc and oxygen;

e) sodium and sulfur;

g) magnesium and sulfur.

3. From what simple substances are formed: A1C1 3, CO 2, ZnS, Na 2 O, CuO, CH 4, Ca 3 P 2?

Write down the reaction equations.

4. Arrange the coefficients in the following schemes of chemical reactions. The sum of all correctly spaced coefficients should be equal to the relative molecular weight of the slaked lime Ca(OH) 2 .

a) Fe (OH) 3  Fe 2 O 3 + H 2 O;

b) A1 2 O 3 + H 2 SO 4  Al 2 (SO 4) 3 + H 2 O;

c) HC1 + Cr 2 O 3  CrCl 3 + H 2 O;

d) Na + H 2 O  NaOH + H 2;

e) A1 + O 2  A1 2 O 3;

f) A1C1 3 + NaOH  Al(OH)3 + NaCl;

g) Fe 2 O 3 + HN O 3  Fe (N O 3) s + H 2 O;

h) A1 + I 2  A1I 3 ;

i) Fe 2 O 3 + H 2  Fe + H 2 O;

j) Fe + Cl 2  FeCl3.

Homework: Study § 20, learn definitions; complete the task: No. 3, 4, 5 pp. 67-68.

Summing up the lesson.

So, today we learned what a chemical equation is. We considered what is needed to draw up a chemical equation.

What did you learn in the lesson, what points need further development?

Write down the chemical equation. As an example, consider the following reaction:

• C 3 H 8 + O 2 –> H 2 O + CO 2
• This reaction describes the combustion of propane (C 3 H 8) in the presence of oxygen to form water and carbon dioxide (carbon dioxide).

Write down the number of atoms of each element. Do this for both sides of the equation. Notice the subscripts next to each element to determine the total number of atoms. Write down the symbol for each element in the equation and note the corresponding number of atoms.

• For example, on the right side of the equation under consideration, as a result of addition, we get 3 oxygen atoms.
• On the left side we have 3 carbon atoms (C 3), 8 hydrogen atoms (H 8) and 2 oxygen atoms (O 2).
• On the right side we have 1 carbon atom (C), 2 hydrogen atoms (H 2) and 3 oxygen atoms (O + O 2).

Chemistry 8 cells

SUMMARY OF THE LESSON ON THE TOPIC: "EQUATIONS OF CHEMICAL REACTIONS".

Lesson type: learning new material

Tasks:

1.Educational: 1) form the concept of the equations of chemical reactions; 2) to begin to form the ability to make equations of chemical reactions.

2.Developing: 1) to develop in students the ability to observe and analyze what they see; 2) to form the skills of self-control of mastering the studied material; 3) to develop the cognitive interest and emotions of students, introducing into the content of the lesson an element of novelty of knowledge, their connection with other subjects, with life; 4) activate students' thinking through conversation and experiment.

3.Educators: 1) the application of the acquired knowledge in the following lessons (types of chemical reactions); 2) to help prevent the fatigue of schoolchildren during the lesson, using such methods of maintaining working capacity as the use of various types of work, demonstration of experiments.

TARGET: Form the concept of the equations of chemical reactions as a conditional notation that reflects the transformation of substances. To begin to form in students the ability to write equations of chemical reactions.

DURING THE CLASSES.

1. Organization of the beginning of the lesson (2 min.).

The topic of today's lesson is "Equations of chemical reactions."

Task: Today we will get acquainted with the conditional notation of chemical reactions - equations. We will learn how to write equations of chemical reactions, as well as arrange the coefficients in them.

2. Checking homework (5 min.).

Let's repeat with you what phenomena are called physical?

Physical phenomena are those in which the size, shape of bodies and the state of aggregation of substances can change, but their composition remains constant.

What are chemical phenomena?

Phenomena, as a result of which others are formed from one substance, are called chemical phenomena, or chemical reactions.

What signs of chemical reactions do you know?

Color change

The appearance of an odor

Precipitation

Dissolution of the precipitate

Gas evolution

The release or absorption of heat, sometimes light is released.

Now, try to guess what these verses are talking about.

3. Preparation for the assimilation of new knowledge (5-7 minutes).

Now I will conduct several experiments, and we will try to draw up a diagram of the observed transformation.

Experience 1. Burning magnesium.

What are you observing? Let's make a diagram of the observed phenomenon.

Magnesium + oxygen → magnesium oxide

starting materials reaction product

This conditional notation is called a reaction scheme. On the left side of the scheme write the starting substances ( i.e., those substances that were taken for interaction), on the right side are the reaction products (i.e., those substances that were formed as a result of the interaction).

Experience 2. Getting carbon dioxide

Put a piece of chalk in a test tube, pour 1-2 ml of hydrochloric acid solution. What are we seeing? What's happening? What are the signs of these reactions?

Using chemical formulas, we will compose a scheme of the observed transformation:

calcium carbonate + hydrochloric acid →

starting materials

CaCO 3 + HCl→

calcium chloride + water + carbon dioxide

reaction products

CaCl 2 + H 2 O + CO 2

4. Assimilation of new material.

Formation of the concept of “coefficients and the ability to arrange coefficients in the equation of a chemical reaction.

Now we will learn about the law of conservation of mass of substances, which was discovered by M.V. Lomonosov in 1756.

The law of conservation of mass of substances (The mass of substances that have entered into a reaction is equal to the mass of substances resulting from it).

The material carriers of the mass of substances are the atoms of chemical elements, because they are not formed and destroyed during chemical reactions, but they are rearranged, then the validity of this law becomes obvious.

The number of atoms of one element on the left side of the equation must be equal to the number of atoms of that element on the right side of the equation.

Task 1 (for groups). Determine the number of atoms of each chemical element involved in the reaction. 1. Calculate the number of atoms:

a) hydrogen: 8NH 3 , NaOH, 6NaOH, 2NaOH, H z PO 4 , 2H 2 SO 4 , 3H 2 S0 4 , 8H 2 SO 4 ;

6) oxygen: C0 2, 3C0 2, 2C0 2, 6CO, H 2 SO 4, 5H 2 SO 4, 4H 2 S0 4, HN0 3.

2. Calculate the number of atoms: a) hydrogen:

1) NaOH + HCl 2) CH 4 + H 2 0 3) 2Na + H 2

b) oxygen:

1) 2CO + 0 2 2) С0 2 + 2Н.О. 3) 4NO 2 + 2H 2 O + O 2

Algorithm for arranging coefficients in the equations of chemical reactions

5. Primary test of knowledge acquisition (8-10 min.). Formation

There are two oxygen atoms on the left side of the diagram, and one on the right side. The number of atoms must be aligned using coefficients. The number of atoms must be aligned with coefficients. Let's summarize the lesson:

1) 2Mg + O 2 → 2MgO

2) CaCO 3 + 2HCl → CaCl 2 + H 2 O + CO 2

Task 2

Fe 2 O 3 + A1 → A1 2 O 3 + Fe;

Mg + N 2 → Mg3N2;

Al+S → A1 2 S 3 ;

A1 + C → A1 4 C 3 ;

Al + Cr 2 0 3 → Cr + A1 2 O 3 ;

Ca+P → Ca 3 P 2 ;

C + H 2 → CH4;

Ca + C → CaC 2 ;

Fe + O2 → Fe 3 O 4 ;

Si+Mg → Mg2Si;

Na+S → Na2S;

CaO + C → CaC2 + CO;

Ca+N2 → Ca 3 N 2 ;

Si + C1 2 → SiCl 4 ;

Ag+S → Ag2S;

Exercise (reserve) 3.

H 2 + C1 2 → HC1;

N 2 + O 2 → NO;

CO 2 + C → CO;

HI → H 2 + 1 2;

Mg + HC1 → MgCl 2 + H 2;

FeS + HC1 → FeCl 2 + H 2 S;

Zn+ HC1 → ZnCl 2 + H 2;

Br2 + KI → KBr+ I 2 ;

Si+HF(r) → SiF 4 + H 2 ;

HCl + Na 2 C0 3 → C0 2 +H 2 O+ NaCl;

KC1O 3 + S → KC1+SO2;

C1 2 + KBr → KC1 + Br2;

SiO 2 + C → Si + CO;

SiO 2 + C → SiC+CO;

Mg + SiO 2 → Mg 2 Si + MgO

Mg 2 Si + HC1 → MgCl 2 + SiH 4

6. Summing up (2 min.).

So, today we got acquainted with the concept "the equation of chemical reactions", learned to arrange the coefficients in these equations on the basis of the law of conservation of mass.

What is a chemical reaction equation?

What is written on the right side of the equation? And on the left?

What does the "+" sign mean in an equation?

Why place coefficients in the equations of chemical reactions?

7. Homework. § 27, ex. 1.3(pis.).

Lesson grades.

Handout:

Arrange the coefficients in the equations of chemical reactions (note that the coefficient changes the number of atoms of only one element):

Fe 2 O 3 + A1 → A1 2 O 3 + Fe;

Mg + N 2 → Mg3N2;

Al+S → A1 2 S 3 ;

A1 + C → A1 4 C 3 ;

Al + Cr 2 0 3 → Cr + A1 2 O 3 ;

Ca+P → Ca 3 P 2 ;

C + H 2 → CH4;

Ca + C → CaC 2 ;

Fe + O2 → Fe 3 O 4 ;

Si+Mg → Mg2Si;

Na+S → Na2S;

CaO + C → CaC2 + CO;

Ca+N2 → Ca 3 N 2 ;

Si + C1 2 → SiCl 4 ;

Ag+S → Ag2S;

Exercise 3 * .

Arrange the coefficients in the equations of chemical reactions (note that the coefficient simultaneously changes the number of atoms of two elements):

H 2 + C1 2 → HC1;

N 2 + O 2 → NO;

CO 2 + C → CO;

HI → H 2 + 1 2;

Mg + HC1 → MgCl 2 + H2