Lesson concept about the rate of chemical reaction of catalysts. Chemistry lesson the rate of chemical reactions. Practical group work

Sections: Chemistry

The purpose of the lesson

  • educational: continue the formation of the concept of "the rate of chemical reactions", derive formulas for calculating the rate of homogeneous and heterogeneous reactions, consider what factors the rate of chemical reactions depends on;
  • developing: teach to process and analyze experimental data; be able to find out the relationship between the rate of chemical reactions and external factors;
  • educational: continue the development of communication skills in the course of pair and team work; to focus the attention of students on the importance of knowledge about the rate of chemical reactions occurring in everyday life (metal corrosion, milk souring, rotting, etc.)

Teaching aids: D. a multimedia projector, a computer, slides on the main issues of the lesson, a CD-ROM "Cyril and Methodius", tables on tables, protocols of laboratory work, laboratory equipment and reagents;

Teaching methods: reproductive, research, partially exploratory;

Form of organization of classes: conversation, practical work, independent work, testing;

Form of organization of student work: frontal, individual, group, collective.

1. Organization of the class

Class readiness for work.

2. Preparation for the main stage of mastering the educational material. Activation of supporting knowledge and skills(Slide 1, see the presentation for the lesson).

The topic of the lesson is “The rate of chemical reactions. Factors Affecting the Rate of a Chemical Reaction ”.

Task: to find out what the rate of a chemical reaction is and what factors it depends on. In the course of the lesson, we will get acquainted with the theory of the question on the above topic. In practice, we will confirm some of our theoretical assumptions.

Predicted student activities

The active work of students shows their readiness to perceive the topic of the lesson. We need knowledge of students about the speed of a chemical reaction from the course of the 9th grade (intra-subject communication).

Let's discuss the following questions (frontally, slide 2):

  1. Why do we need knowledge about the rate of chemical reactions?
  2. What examples can confirm that chemical reactions proceed at different rates?
  3. How is the speed of mechanical movement determined? What is the unit of measure for this speed?
  4. How is the rate of a chemical reaction determined?
  5. What conditions must be created for a chemical reaction to start?

Let's consider two examples (the experiment is conducted by the teacher).

On the table there are two test tubes, in one a solution of alkali (KOH), in the other - a nail; pour the CuSO4 solution into both test tubes. What are we seeing?

Predicted student activities

Using examples, students judge the speed of reactions and draw appropriate conclusions. Writing the reactions done on the board (two students).

In the first test tube, the reaction occurred instantly, in the second - there are no visible changes yet.

Let's compose the reaction equations (two students write equations on the board):

  1. CuSO 4 + 2KOH = Cu (OH) 2 + K 2 SO 4; Cu 2+ + 2OH - = Cu (OH) 2
  2. Fe + CuSO 4 = FeSO 4 + Cu; Fe 0 + Cu 2+ = Fe 2+ + Cu 0

What conclusion can we draw from the reactions carried out? Why is one reaction instant and the other slow? To do this, it is necessary to remember that there are chemical reactions that occur throughout the entire volume of the reaction space (in gases or solutions), and there are others that occur only on the contact surface of substances (combustion of a solid in a gas, interaction of a metal with an acid, salt of a less active metal ).

Predicted student activities

Based on the results of the demonstrated experiment, the students conclude: reaction 1 is homogeneous, and reaction

2 - heterogeneous.

The rates of these reactions will be mathematically determined in different ways.

The study of the rates and mechanisms of chemical reactions is called chemical kinetics.

3. Assimilation of new knowledge and methods of action(Slide 3)

The reaction rate is determined by the change in the amount of substance per unit of time

In unit V

(for homogeneous)

On a unit surface of contact of substances S (for heterogeneous)

Obviously, with such a definition, the value of the reaction rate does not depend on the volume in a homogeneous system and on the contact area of ​​reagents in a heterogeneous system.

Predicted student activities

Active actions of students with the object of study. Entering the table in the notebook.

Two important points follow from this (slide 4):

2) the calculated value of the speed will depend on what substance it is determined by, and the choice of the latter depends on the convenience and ease of measuring its amount.

For example, for the reaction 2Н 2 + О 2 = 2Н 2 О: υ (according to Н 2) = 2 υ (according to О 2) = υ (according to Н 2 О)

4. Consolidation of primary knowledge about the rate of a chemical reaction

To consolidate the material considered, we will solve the computational problem.

Predicted student activities

Initial understanding of the knowledge gained about the reaction rate. Correctness of the solution to the problem.

Task (slide 5). The chemical reaction takes place in solution, according to the equation: A + B = C. Initial concentrations: substance A - 0.80 mol / l, substance B - 1.00 mol / l. After 20 minutes, the concentration of substance A dropped to 0.74 mol / l. Determine: a) the average reaction rate for this period of time;

b) the concentration of substance B after 20 minutes. Solution (Appendix 4, slide 6).

5. Assimilation of new knowledge and methods of action(conducting laboratory work in the course of repetition and study of new material, in stages, Appendix 2).

We know that various factors affect the rate of a chemical reaction. Which?

Predicted student activities

Reliance on the knowledge of grades 8-9, writing in a notebook in the course of studying the material. List (slide 7):

The nature of the reactants;

Temperature;

Concentration of reactants;

The action of catalysts;

Contact surface of reactants (in heterogeneous reactions).

The influence of all the listed factors on the reaction rate can be explained using a simple theory - collision theory (slide 8). Its main idea is as follows: reactions occur when particles of reagents collide, which have a certain energy.

From here we can draw conclusions:

  1. The more reagent particles, the closer they are to each other, the more chances they have to collide and react.
  2. Only lead to a reaction effective collisions, those. those in which "old ties" are destroyed or weakened and therefore "new" ones can form. But for this, the particles must have sufficient energy.

The minimum excess energy (over the average energy of particles in the system) required for effective collision of particles in the system) required for effective collision of reagent particles is calledactivation energy E a.

Predicted student activities

Comprehension of the concept and writing the definition in a notebook.

Thus, there is a certain energy barrier on the way of all the particles entering into the reaction, which is equal to the activation energy. If it is small, then there are many particles that successfully overcome it. With a large energy barrier, additional energy is needed to overcome it, sometimes a good "push" is enough. I light a spirit lamp - I give extra energy E a, necessary to overcome the energy barrier in the reaction of interaction of alcohol molecules with oxygen molecules.

Consider factors, which affect the reaction rate.

1) The nature of the reacting substances(slide 9) The nature of the reacting substances is understood as their composition, structure, the mutual influence of atoms in inorganic and organic substances.

The magnitude of the activation energy of substances is a factor through which the influence of the nature of the reacting substances affects the reaction rate.

Briefing.

Independent formulation of conclusions (Appendix 3 at home)

During the classes

I. Organization of the beginning of the lesson.

II. Preparation for the main stage of the lesson.

III. Concretization of knowledge, consolidation of methods of action, systematization of knowledge about the laws with which it is possible to control chemical reactions.

IV. Summing up the results of the lesson, information about homework.

I. Organization of the beginning of the lesson

Stage objective: prepare students for classroom work.

Teacher: Today we will continue our study of the topic "The rate of a chemical reaction" and find out whether a person, possessing certain knowledge, can control a chemical reaction. To solve this problem, we go to a virtual laboratory. To enter it, you must show your knowledge of the rate of a chemical reaction.

II. Preparation for the main stage of the lesson

Stage objectives: updating basic knowledge and skills, ensuring motivation and acceptance by students of the goal of the lesson.

Updating students' knowledge

The teacher organizes a frontal conversation:

Question 1: What does chemical kinetics study?

Supposed answer: chemical kinetics - the science of the laws governing the course of chemical reactions in time.

Question 2: into which two groups can the reactions be divided depending on the state of the chemicals?

Supposed answer: if chemical reactions take place in a homogeneous medium, for example in solution or in the gas phase, they are called homogeneous. And if the reaction takes place between substances in different states of aggregation, they are called heterogeneous.

Question 3: how to determine the rate of a heterogeneous reaction?

Supposed answer: the rate of a heterogeneous reaction is defined as the change in the amount of substance per unit of time per unit of surface (the student writes down the formula on the blackboard)

Question 4: how to determine the rate of a homogeneous reaction?

Supposed answer: The rate of a homogeneous reaction is defined as the change in the concentration of one of the substances per unit of time (the student writes the formula on the board).

Teacher: now, using your life experience, suppose:

Question 5: Which will burn faster: wood plank or wood shavings?

Supposed answer: wood shavings will burn faster.

Question 6: where will coal burn faster: in air or in oxygen?

Supposed answer: faster coal will burn in oxygen.

III. Concretization of knowledge, consolidation of methods of action, systematization of knowledge about the laws with which it is possible to control chemical reactions.

Stage objective: ensure the assimilation of knowledge and methods of action by organizing an active productive activity of students.

Introductory story of the teacher (accompanied by a computer presentation):

Teacher: using your life experience, you guessed correctly. Indeed, the rate of a chemical reaction depends on many factors. The main ones are: the nature and concentration of reactants, pressure, temperature, contact surface of reactants, the effect of catalysts.

We will also use the information in the tutorial as we proceed.

The students, under the guidance of the teacher, solve each experimental problem, and the teacher, using the computer presentation, leads the students to informed conclusions.

Result of work:


Securing the material.

Problem: For the reaction, substances were taken at a temperature of 40 C, then they were heated to 70 C. How will the rate of a chemical reaction change if its temperature coefficient is 2?

Answer: the speed of the chemical reaction will increase by 8 times.

Teacher: So, what conclusion can we draw: can a person control the speed of reactions?

Supposed answer: yes, maybe if he has knowledge of chemical kinetics.

IV. Lesson summary, homework information

Stage objectives: evaluate the work in the lesson and show the value of the work done for the subsequent study of the topic.

Teacher: Let's recall the course of the lesson, what have we learned today, what have we learned?

Reflection. Students' statements.

Teacher: homework: paragraph 6.1, learn the table information. Complete exercises 5, 6, 8 on pages 108-109.

Technological map of the lesson "The rate of chemical reactions"

The main points of the technological map

Mandatory general part

Name of the discipline

Lesson topic

Chemical reaction rate

Type and type of occupation

Combined lesson

Repetition, lecture

Lesson objectives

(as expected learning outcomes)

As a result of the lesson, the students:

continue to form the concept of "the rate of chemical reactions", find out what factors the rate of chemical reactions depends on;

continue to learn to process and analyze experimental data; find out the relationship between the rate of chemical reactions and external factors;

continue to develop communication skills in the course of pair and team work; to focus on the importance of knowledge about the rate of chemical reactions occurring in everyday life (metal corrosion, sour milk, rotting, etc.)

reinforce the ability to work with an electronic manual, tables, reference material, additional literature

Teaching methods

Partially - search (reproductive)

Formed competencies (general competencies (GC) and professional competencies (PC))

General: to formulate their values ​​in relation to the studied disciplines and fields of activity;

be able to make decisions, take responsibility for their consequences;

carry out an individual educational trajectory taking into account general requirements and norms;

own different types of speech activity.

Professional: have the skills to work with various sources of information (electronic manual, Internet, dictionaries, reference books, books, textbooks);

independently search, extract, analyze and select the information necessary for solving educational problems;

navigate information flows, be able to consciously perceive information;

possess the skills to use information devices (PC, printer);

apply information and telecommunication technologies to solve educational problems: audio and video recording, e-mail, the Internet;

be able to apply the acquired knowledge in practice.

Thesaurus field of study

Chemical kinetics is a branch of chemistry that studies the rates and mechanisms of chemical reactions.

A system in chemistry is a substance under consideration or a collection of substances.

A phase is a part of a system that is separated from other parts by an interface.

Homogeneous (homogeneous) system - a system consisting of one phase.

Heterogeneous (inhomogeneous) system - a system consisting of two or more phases.

The rate of a homogeneous chemical reaction is the amount of a substance entering into a reaction or formed as a result of a reaction per unit time per unit volume of the system.

The rate of a heterogeneous chemical reaction is the amount of a substance entering into a reaction or formed as a result of a reaction per unit of time per unit of interface.

Factors affecting the reaction rate:

The nature of the reactants;

Concentration of reactants;

Temperature;

The presence of catalysts.

A catalyst is a substance that changes (increases) the reaction rate, but is not consumed as a result of the reaction.

An inhibitor is a substance that changes (slows down) the reaction rate, but is not consumed as a result of the reaction.

Enzymes (enzymes) are biological catalysts.

The law of the acting masses.

The means used, incl. ICT tools

Computer terminal, multimedia projector, demonstration screen, laptop, speakers, 15 personal computers, CD with presentations and demonstration of experiments on salt hydrolysis; basic and additional literature

Interdisciplinary and intercourse links

Interdisciplinary: biology (chemical reactions in a living organism), physics (the concept of the thermal effect of reactions, the influence of physical factors on the rate of a chemical reaction)

Educational resources (including the Internet)

E-learning system "Academy-Media", chemical sites XuMuk.ru, Alhimik.ru, Useful information on chemistry, basic and additional literature

Stages of the lesson

Stage duration

results

Criteria and method of assessment

Teacher function

Organization of student activities

Organization of the beginning of the lesson

Greetings

Checking the preparation of students for the lesson

Equipment readiness

EO system launch

Identifying absent students

Greetings

The attendant calls absent students

Homework check

Issuing cards with an individual task, displaying tasks for the whole group

Performing assignments, self-test and verification in pairs

The stage of preparing students for active and conscious assimilation of new material

Announcement of the topic of the lesson and definition of its objectives

Writing a topic in a notebook

Search for the relevant topic in the EO system

Knowledge update, motivational stage

Frontal conversation

Asking questions

Discussion management

Answers to questions, complementing each other's answers

The stage of assimilation of new knowledge

Issuance of assignments in an electronic manual, consultations

Working with the electronic manual

Primary examination of the assimilation of knowledge

Issuance of assignments, control of implementation

Completing assignments

Primary consolidation of knowledge

Demonstration of experiments on the topic using a projector and a screen

Observation

Formulation of reaction equations

Control and self-examination of knowledge. Reflexive control stage

Control of writing equations, evaluation, generalization

Self-test, conclusions

Summing up the results of the lesson

Analysis of the success of achieving the goal of the lesson

Assessment of future work prospects

Homework information, instructions on how to complete it

Issuing homework

Conducting a briefing on its implementation

Recording homework, questions to clarify it



O.I. Ivanova, teacher of chemistry MBOU "Napolnokotyakskaya secondary school" of the Kanash district of the Chechen Republic

Lesson "Factors affecting the rate of chemical reaction"

The purpose of the lesson: study of factors affecting the rate of a chemical reaction

Tasks:

find out what factors influence the rate of chemical reactions

teach to explain the influence of each factor;

stimulate the cognitive activity of students by creating a problem situation;

to form the competence of schoolchildren (educational and cognitive, communicative, health preservation);

improve the practical skills of students.

Lesson type: problem-dialogical.

Forms of work: group, individual.

Equipment and reagents: a set of test tubes, a holder for test tubes, a stand, an alcohol lamp, a splinter, matches, zinc granules, zinc powder, copper oxide powder, magnesium, sulfuric acid solution (10% solution), hydrogen peroxide, potassium dichromate, copper sulfate, iron nail, sodium hydroxide, chalk.

During the classes:

1st stage:

Call: Hello guys! Today we will introduce ourselves as scientists-researchers. But before we start studying new material, I would like to demonstrate a small experiment. Please look at the board and make your assumptions about the course of these reactions:

A) copper and iron sulfate;

B) a solution of copper sulfate and potassium hydroxide

Will these reactions take place? Please go out to the blackboard and write down the equations of these reactions.

Consider these examples (the experiment is conducted by the teacher).

On the table there are two test tubes, both contain a solution of copper sulfate, but in one test tube with the addition of sodium chloride, we drop an aluminum granule into both test tubes. What are we seeing?

PROBLEM: Why, in the second case, we do not see signs of a reaction, are our assumptions wrong?

OUTPUT: Chemical reactions take place at different rates. Some go slowly, for months, such as iron corrosion or fermentation (fermentation) of grape juice, resulting in wine. Others are completed in a few weeks or days, such as alcoholic fermentation of glucose. Still others end very quickly, for example, the precipitation of insoluble salts, and some proceed instantly, such as explosions.

Almost instantaneously, very quickly, many reactions proceed in aqueous solutions: these are ionic reactions proceeding with the formation of a precipitate, a gas, or a neutralization reaction.

Now let's remember what you know about the rate of chemical reactions.

Comprehension of the concept. List the definition, formulas, unit of measurement.

PROBLEM: What do you need to know to be able to control the rate of a chemical reaction? (Know what conditions affect speed)

What are the names of these conditions that you have just listed? (Factors)

There are chemical devices and reagents on the tables in front of you. What do you think, for what purpose you will conduct experiments? (In order to study the influence of factors on the speed of reactions)

Now we come to the topic of today's lesson. It is the study of factors that we will deal with in this lesson.

We write the title of the topic and the date in the notebooks.

IIstage:

MEANING OF THE CONTENT.

What factors affect the rate of chemical reactions?

Students list: temperature, nature of reactants, concentration, contact surface, catalysts.

How can they change the reaction rate?(Students offer their guesses)

Teacher: The influence of all these factors on the rate of chemical reactions can be explained using a simple theory - the theory of collisions. Its main idea is as follows: reactions occur when particles of reagents collide, which have a certain energy. From here we can draw the following conclusions:

The more reagent particles there are, the more chances they have to collide and react.

Only effective collisions lead to a reaction, i.e. those in which "old ties" are destroyed or weakened and therefore "new" ones can form. But for this, the particles must have a certain energy.

The minimum excess energy required for effective collision of reagent particles is called the activation energy (recording the definition in notebooks).

Thus, on the path of all particles entering into the reaction, there is a certain barrier equal to the activation energy. If it is small, then there are many particles that successfully overcome it. With a large energy barrier, additional energy is needed to overcome it, sometimes a "good push" is enough.

We turn to the statement of Leonardo da Vinci (Knowledge that has not been tested by experience is fruitless and full of mistakes).

Teacher: How do you understand the meaning of these words?(test theory with practice)

Yes, indeed, any theory must be tested in practice as well. Next, you yourself have to study various factors on the speed of reactions. To do this, you will conduct reactions, guided by the instructions on your tables, draw up an experiment protocol. After that, one student from the group will need to go to the blackboard, explain the influence of which factor you considered, write equations on the blackboard and draw a conclusion according to collision theory and activation theory.

Safety briefing.

CONDUCTING PRACTICAL WORK IN GROUPS

Card 1: Factors affecting the rate of a chemical reaction:

1. The nature of the reacting substances.

Pour some sulfuric acid into two test tubes.

2. Dip a small amount of magnesium into one, and a zinc granule into the other.

3. Compare the rate of interaction of various metals with sulfuric acid.

4. What, in your opinion, is the reason for the different rates of acid reactions with these metals.

5. The influence of what factor did you find out during this work?

6. Find in the laboratory protocol the half-reactions corresponding to your experience and add the reaction equations.

Card 2. Factors affecting the rate of a chemical reaction:

2. Concentration of reactants.

Be careful when handling substances. Remember the safety rules.

1. Pour 1-2 ml of sulfuric acid into two test tubes.

2. Add the same volume of water to one of the tubes.

3. Place a zinc pellet in each tube.

4. In which test tube did hydrogen evolution start faster?

Card 3. Factors affecting the rate of a chemical reaction:

3. The area of ​​contact of the reacting substances.

Be careful when handling substances. Remember the safety rules.

1. Grind a small piece of chalk in a mortar.

2. Pour a little sulfuric acid solution into two test tubes. Be very careful, add very little acid!

3. Simultaneously place the powder in one tube and a piece of chalk in the other.

4. In which test tube will the reaction be faster?

5. The influence of which factor did you find out in this experiment?

6. How can this be explained in terms of collision theory?

7. Write the reaction equation.

Card 4. Factors affecting the rate of a chemical reaction:

4. Temperature.

Be careful when handling substances. Remember the safety rules.

1. Pour the sulfuric acid solution into both tubes and place in them one by one a copper oxide pellet.

2. Warm one of the tubes gently. First, we heat the test tube slightly obliquely, trying to warm it up along its entire length, then only the lower part, having already straightened the test tube. Hold the tube with a holder.

3. In which test tube is the reaction proceeding more intensively?

4. The influence of which factor did you find out in this experiment?

5. How can this be explained in terms of collision theory?

6. Write the reaction equation.

Card 5. Factors affecting the rate of a chemical reaction:

5. The presence of special substances - catalysts, substances that increase the rate of a chemical reaction.

Be careful when handling substances. Remember the safety rules.

Pour hydrogen peroxide into two glasses.

In one of the tubes, carefully sprinkle a few crystals of potassium dichromate. Stir the resulting solution with a glass rod.

Light a splinter, and then extinguish it. Bring the smoldering splinter to the solutions in both glasses as close to the solution as possible without touching the liquid. The speck should catch fire.

In which test tube is there rapid gas evolution? What kind of gas is it?

What role does potassium dichromate play in this reaction?

The influence of which factor did you find out in this experiment?

Write the reaction equation.

DISCUSSION OF THE OBTAINED RESULTS.

For discussion from each working group, one student comes to the board (in turn)

Drawing up a summary protocol of laboratory work based on the answers to the questions of the workshop.

The reaction equations are written on the board and the appropriate conclusions are drawn. All other students enter the findings and equations in the minutes.

Influence of the nature of reactants

Problem:

Teacher: the masses of the taken substances of the sample of solids, the concentration of hydrochloric acid, the reaction conditions are the same, but the intensity of the ongoing processes (the rate of hydrogen evolution) is different?

Discussion:

Students: we took different metals.

Teacher: all substances are made up of atoms of chemical elements. What is the difference between chemical elements according to your knowledge of the Periodic Law and the Periodic Table of D.I.Mendeleev?

Students: Serial number, position in the Periodic Table of D. I. Mendeleev, that is, they have a different electronic structure, and therefore the simple substances formed by these atoms have different properties.

Teacher: that is, these substances are of a different nature. Thus, the rate of a chemical reaction will depend on the nature of a particular reacting substance, since they have different structures and properties.

Output:

Students: The rate of a chemical reaction will depend on the nature of the reacting substances: the more active the metal (substance), the higher the rate of the chemical reaction.

Effect of concentration

Problem: the nature of all reacting substances, the conditions for the experiment are the same, but the intensity of the ongoing processes (the rate of hydrogen evolution) is different?

Discussion:

Teacher: Why is the rate of a chemical reaction different, because substances of the same chemical nature react?

Students: When adding water, we changed (decreased) the concentration of sulfuric acid in one test tube, while the rate of hydrogen evolution decreased.

Output:

Students: The rate of a chemical reaction will depend on the concentration of the reactants: the greater the concentration of the reactants, the higher the rate of the chemical reaction.

Explanation of the teacher: CONCENTRATION OF REACTIVE SUBSTANCES.

The more reagent particles, the closer they are to each other, the more chances they have to collide and react. Based on a large amount of experimental material in 1867. Norwegian scientists K. Guldberg and P. Vaage and independently of them in 1865 the Russian scientist N. I. Beketov formulated the basic law of chemical kinetics, which establishes the dependence of the reaction rate on the concentrations of reacting substances:

The reaction rate is proportional to the product of the concentrations of the reactants taken in powers equal to their coefficients in the reaction equation.

This law is also called the law of the masses in action.It is only valid for gaseous and liquid substances!

2A + 3B = A2B3 V = k * CA2 * .CB3

Exercise 1. Write kinetic equations for the following reactions:

Task 2.

How will the reaction rate change with the kinetic equation

v = kCA2CB, if the concentration of substance A is increased by 3 times.

Dependence on the surface area of ​​the reactants

Problem:

Teacher: all substances are the same in their chemical nature, the same in mass and concentration, react at the same temperature, but the intensity of hydrogen evolution (and hence the rate) is different.

Discussion:

Students: A piece and a chalk powder of the same weight have different occupied volumes in a test tube, different degrees of grinding. Where this degree of refinement is greatest, the rate of hydrogen evolution is maximum.

Teacher: this characteristic is the area of ​​the contact surface of the reacting substances. In our case, the surface area of ​​contact of calcium carbonate with a solution of H2SO4 is different.

Output:

Students: The speed of a chemical reaction depends on the contact area of ​​the reacting substances: the larger the contact area of ​​the reacting substances (degree of grinding), the greater the reaction rate.

Teacher: Such a dependence is not always observed: so for some heterogeneous reactions, for example, in the Solid-Gas system, at very high temperatures (more than 500 ° C), highly crushed (to powder) substances are able to sinter, thereby reducing the contact surface area of ​​the reacting substances.

Influence of temperature

Problem:

Teacher: the substances taken for the experiment have the same nature, the mass of the taken CuO powder and the concentration of sulfuric acid are also the same, but the reaction rate is different.

Discussion:

Students: This means that when the temperature of the reaction changes, we also change its rate.

Teacher: Does this mean that as the temperature rises, the rate of all chemical reactions will increase?

Students: No. Some reactions take place at very low and even sub-zero temperatures.

Output:

Students: Consequently, any change in temperature by several degrees will significantly change the rate of the chemical reaction.

Teacher: This is practically how the Van't Hoff's law sounds, which will act here: When the reaction temperature changes by every 10 ºС, the rate of the chemical reaction changes (increases or decreases) by 2-4 times.

Teacher's comment: TEMPERATURE

The higher the temperature, the more active particles, the speed of their movement increases, which leads to an increase in the number of collisions. The reaction speed increases.

Van't Hoff's rule:

With an increase in temperature for every 10 ° C, the total number of collisions increases only by ~ 1.6%, and the reaction rate increases by 2-4 times (by 100-300%).

The number showing how many times the reaction rate increases when the temperature rises by 10 ° C is called the temperature coefficient.

Van't Hoff's rule is mathematically expressed by the following formula:

whereV1 -speed of reaction at temperaturet2 ,

V2 - reaction rate at temperaturet1 ,

y- temperature coefficient.

Solve the problem:

Determine how the rate of some reaction will change when the temperature rises from 10 to 500C. The temperature coefficient of the reaction is 3.

Solution:

substitute task data into the formula:

the reaction rate will increase 81 times.

Effect of catalyst

Problem:

Teacher: the substance in both cases is the same, the nature is the same, at the same temperature, the concentration of the reagent is the same, why is the speed different?

Discussion:

Teacher: Such substances that accelerate chemical reactions are called catalysts. There are substances that slow down reactions, they are called inhibitors.

Output:

Students: catalysts increase the reaction rate by decreasing the activation energy. The lower the activation energy, the faster the reaction.

Catalytic phenomena are widespread in nature: respiration, assimilation of nutrients by cells, protein synthesis, etc. are processes regulated by biological catalysts - enzymes. Catalytic processes are the basis of life in the form that exists on earth.

Parable "The Eighteenth Camel" (to explain the role of the catalyst)

(a very ancient Arabic parable)

Once upon a time there lived in the East a man who bred camels. He worked all his life, and when he got old, he called his sons to him and said:
“My children! I have become old and weak and will soon die. After my death, divide the remaining camels as I tell you. You, the eldest son, worked the hardest - take for yourself half of the camels. You, the middle son, have just started helping me - take yourself a third part. And you, junior, take the ninth part. "
Time passed and the old man died. Then the sons decided to divide the inheritance as their father bequeathed to them. They drove the herd into a large field, counted, and it turned out that there were only seventeen camels in the herd. And it was impossible to divide them by either 2, or 3, or 9! Nobody knew what to do. The sons began to argue, and each offered his own solution. And they were already tired of arguing, but did not come to a common decision.
At this time, a traveler was riding by on his camel. Hearing a shout and an argument, he asked: "What happened?"
And the sons told about their misfortune. The traveler got off the camel, let him into the herd and said: "Now separate the camels as your father ordered."
And since there were 18 camels, the eldest son took for himself half, that is, 9, the middle one - a third, that is, 6 camels, and the youngest one ninth, that is, two camels. And when they divided the flock in this way, one more camel remained in the field, because 9 + 6 + 2 equals 17.
And the traveler got on his camel and drove on.

Laboratory work (protocol)

Observations
Dependence of the reaction rate on the nature of the reacting substances

Zn + H2SO4 (10%) =

Mg + H2SO4 (10%) =

 V 1 V 2

The dependence of the reaction rate on the concentration of reactants

Zn + H2SO4 (10%) =

 V 1 V 2
Dependence of the reaction rate on the surface area of ​​the reactants for heterogeneous reactions

Zn (granules) + H2SO4 (10%) =

Zn (powder) + H2SO4 (10%) =

 V 1 V 2
The dependence of the reaction rate on temperature CuO + H 2 SO 4 (10%) = CuO + H 2 SO 4 (10%) heating = V 1 V 2
Dependence of the reaction rate on the presence of a catalyst

K 2 Cr 2 O 7

 V 1 V 2

REFLECTION.

What have we learned in this lesson?

Make a cluster on the topic "Factors affecting XP speed."

Why do we need knowledge about the factors affecting the rate of chemical reactions?

Are they used in everyday life? If applicable, name areas of application.

Test on the topic (for 5 minutes).

Test

1. The rate of a chemical reaction characterizes:

1) the movement of molecules or ions of reacting substances relative to each other

2) the time it takes for the chemical reaction to end

3) the number of structural units of a substance that have entered into a chemical reaction

4) change in the amount of substances per unit of time in a unit of volume

With an increase in the temperature of the reacting substances, the rate of the chemical reaction:

1) decreases

2) increases

3) does not change

4) changes periodically

With an increase in the surface area of ​​contact of the reacting substances, the rate of the chemical reaction:

1) decreases

2) increases

3) does not change

4) changes periodically

With an increase in the concentration of reactants, the rate of the chemical reaction:

1) decreases

2) increases

3) does not change

4) changes periodically

To increase the speed of a chemical reaction
2CuS (tv.)+ 3O2 (G.) = 2CuO (tv.) + 2SO2 (G.) + Qnecessary:

1) increase the concentration of SO2

2) reduce the concentration of SO2

3) reduce the temperature

4) increase the fineness of CuS

Under normal conditionsat the lowest speedthere is an interaction between:

3) Zn and HCl (10% solution)

4) Mg and HCl (10% solution)

With an increase in temperature from 10 to 30 ° C, the reaction rate, the temperature coefficient of which = 3:

1) increases by 3 times

2) increases 9 times

3) decreases 3 times

4) decreases 9 times

Test Work Evaluation:

Test answers:

No errors - "5"

1-2 errors - "4"

3 errors - "3"

Homework:

§13, p. 135-145.

O.S. Gabrielyan, G. G. Lysova. Chemistry. Grade 11. Textbook for educational institutions. 11th edition, stereotyped. M .: Bustard, 2009.

For the reaction, substances were taken at a temperature of 400C, and then they were heated to 70C. How will the rate of a chemical reaction change if its temperature coefficient is 2?

How the rate of the reaction proceeding according to the equation 2NO + O2 = 2NO2 will change if the concentration of both substances is increased by 3 times.

Date _____________ Class _______________
Theme: The concept of the rate of a chemical reaction. Catalysts. Chemical equilibrium
Lesson objectives: to repeat and consolidate knowledge about reversible reactions, chemical equilibrium; to form ideas about catalysts and catalysis.

During the classes

1. Organizational moment of the lesson. 2. Learning new material You are familiar with the concept of "speed" from a physics course. In general terms, speed is a quantity that shows how any characteristic changes per unit of time.The rate of a chemical reaction is a value that shows how the concentrations of the starting substances or reaction products change per unit of time. To estimate the rate, it is necessary to change the concentration of one of the substances.1. Of greatest interest are reactions proceeding in a homogeneous (homogeneous) medium.Homogeneous systems (homogeneous) - gas / gas, liquid / liquid - reactions are in full swing. Mathematically, the rate of a chemical homogeneous reaction can be represented using the formula:
2. For a heterogeneous reaction, the reaction rate is determined by the number of moles of substances entering or forming as a result of the reaction per unit of time per unit of surface:Heterogeneous (heterogeneous) systems - solid / liquid, gas / solid, liquid / gas - the reactions take place at the interface. Thus, the rate of a chemical reaction shows the change in quantity substances per unit time, per unit volume or per unit interface. Dependence of the reaction rate on various factors

Conditions

Mass action law The rate of a chemical reaction is directly proportional to the product of the concentrations of the reactants. With an increase in the concentration of at least one of the reacting substances, the rate of the chemical reaction increases in accordance with the kinetic equation.
Consider the general reaction equation: aA + bB = cC + dD, where A, B, C, D - gases, liquidsFor this reaction, the kinetic equation takes the form:

The reason for the increase in speed is an increase in the number of collisions of reacting particles due to the increase in particles per unit volume.

Chemical reactions occurring in homogeneous systems (mixtures of gases, liquid solutions) are carried out due to the collision of particles. However, not every collision of reagent particles leads to the formation of products. Only particles with increased energy -active particles, able to carry out the act of a chemical reaction. As the temperature rises, the kinetic energy of the particles increases and the number of active particles increases; therefore, chemical reactions at high temperatures proceed faster than at low temperatures. The dependence of the reaction rate on temperature is determined by the Van't Hoff rule:when the temperature rises for every 10 ° C, the reaction rate increases by 2-4 times.

The Van't Hoff rule is approximate and is applicable only for a rough estimate of the effect of temperature on the reaction rate.

Catalysts are substances that increase the rate of a chemical reaction.They interact with reagents to form an intermediate chemical compound and are released at the end of the reaction.
The effect of catalysts on chemical reactions is calledcatalysis ... According to the state of aggregation in which the catalyst and reactants are located, one should distinguish between:
homogeneous catalysis (the catalyst forms a homogeneous system with the reactants, for example, a gas mixture);
heterogeneous catalysis (catalyst and reactants are in different phases; catalysis occurs at the interface).

A substance that slows down the reaction rate

1. Among all known reactions, there are reversible and irreversible reactions. When studying the reactions of ion exchange, the conditions under which they proceed to the end were listed. ( ). There are also known reactions that do not go to the end under the given conditions. So, for example, when sulfur dioxide dissolves in water, the reaction occurs: SO 2 + H 2 O→ H 2 SO 3 ... But it turns out that only a certain amount of sulfurous acid can form in an aqueous solution. This is due to the fact that sulfurous acid is fragile, and the opposite reaction occurs, i.e. decomposition into sulfur oxide and water. Consequently, this reaction does not go to the end because two reactions occur simultaneously -straight (between sulfur oxide and water) andreverse (decomposition of sulfurous acid). SO 2 + H 2 O↔ H 2 SO 3 . Chemical reactions proceeding under given conditions in mutually opposite directions are called reversible.
2. Since the rate of chemical reactions depends on the concentration of the reacting substances, then at first the rate of the direct reaction( υpr ) should be maximum,and the reaction rate (υ arr ) is equal to zero. The concentration of the reactants decreases over time, and the concentration of the reaction products increases. Therefore, the speed of the forward reaction decreases, and the speed of the reverse reaction increases. At a certain point in time, the rates of forward and reverse reactions become equal:
In all reversible reactions, the rate of the forward reaction decreases, the rate of the reverse reaction increases until both rates become equal and a state of equilibrium is established: υ pr = υ arr The state of the system at which the rate of the forward reaction is equal to the rate of the reverse reaction is called chemical equilibrium. In a state of chemical equilibrium, the quantitative ratio between the reactants and the reaction products remains constant: how many molecules of the reaction product per unit time are formed, so many of them decompose. However, the state of chemical equilibrium is maintained as long as the reaction conditions remain unchanged: concentration, temperature and pressure. Quantitatively, the state of chemical equilibrium is describedthe law of the masses in action. In equilibrium, the ratio of the product of the concentrations of the reaction products (in powers of their coefficients) to the product of the concentrations of the reagents (also in powers of their coefficients) is a constant value that does not depend on the initial concentrations of substances in the reaction mixture.This constant is calledequilibrium constant - k So for the reaction: N 2 (D) + 3 H 2 (G)↔ 2 NH 3 (G) + 92.4 kJthe equilibrium constant is expressed as follows:υ 1 = υ 2 υ 1 (direct reaction) = k 1 [ N 2 ][ H 2 ] 3 , where - equilibrium molar concentration, = mol / l υ 2 (feedback) = k 2 [ NH 3 ] 2 k 1 [ N 2 ][ H 2 ] 3 = k 2 [ NH 3 ] 2 K p = k 1 / k 2 = [ NH 3 ] 2 / [ N 2 ][ H 2 ] 3 – equilibrium constant . Chemical equilibrium depends - on concentration, pressure, temperature. Principle determines the direction of mixing equilibrium:If an external effect has been exerted on a system in equilibrium, then the balance in the system will shift in the direction opposite to this effect. 1) Effect of concentration - if the concentration of the starting materials is increased, then the equilibrium shifts towards the formation of reaction products.For example, K p = k 1 / k 2 = [ NH 3 ] 2 / [ N 2 ][ H 2 ] 3 When added to the reaction mixture, for example nitrogen, i.e. the concentration of the reagent increases, the denominator in the expression for K increases, but since K is a constant, the numerator must also increase in order to fulfill this condition. Thus, the amount of the reaction product increases in the reaction mixture. In this case, one speaks of a shift in chemical equilibrium to the right, towards the product. Thus, an increase in the concentration of reagents (liquid or gaseous) displaces towards the products, i.e. towards a direct reaction. An increase in the concentration of products (liquid or gaseous) shifts the equilibrium towards the reactants, i.e. in the direction of the reverse reaction. A change in the mass of a solid does not change the equilibrium position. 2) Influence of temperature - an increase in temperature shifts the equilibrium towards the endothermic reaction.a) N 2 (D) + 3 H 2 (G) ↔ 2 NH 3 (G) + 92.4 kJ (exothermic - heat release) As the temperature rises, the equilibrium will shift towards the ammonia decomposition reaction ( ← ) b) N 2 (D) + O 2 (G) ↔ 2 NO (G) - 180.8 kJ (endothermic - heat absorption) As the temperature rises, the equilibrium will shift towards the formation reaction NO ( → ) 3) Influence of pressure (only for gaseous substances) - with increasing pressure, the equilibrium shifts towards the formation of substances that occupy a smaller volume.N 2 (D) + 3 H 2 (G) ↔ 2 NH 3 (G) 1 V - N 2 3 V - H 2 2 V – NH 3 With increasing pressure ( P ): before reaction 4 V gaseous substances → after reaction 2 V gaseous substances, therefore, the equilibrium shifts to the right ( → ) With an increase in pressure, for example, 2 times, the volume of gases decreases by the same number of times, and therefore, the concentration of all gaseous substances will increase 2 times. K p = k 1 / k 2 = [ NH 3 ] 2 / [ N 2 ][ H 2 ] 3 In this case, the numerator of the expression for K will increase by 4 times, and the denominator is 16 times, i.e. equality will be violated. To restore it, concentration must increase. ammonia and decrease in concentration nitrogen and hydrogen. The balance will shift to the right. So, with increasing pressure, the equilibrium shifts towards a decrease in volume, with a decrease in pressure - towards an increase in volume. The change in pressure has practically no effect on the volume of solid and liquid substances, i.e. does not change their concentration. Consequently, the equilibrium of reactions in which gases do not participate is practically independent of pressure. ! The course of a chemical reaction is influenced by substances - catalysts. But when using a catalyst, the activation energy of both direct and reverse reactions decreases by the same amount and therefore the balance does not shift. 3. Consolidation of the studied material Task Indicate how it will affect:a) pressure increase;b) temperature rise;c) an increase in the oxygen concentration for the equilibrium of the system: 2 CO (g) + O 2 (g) ↔ 2 CO 2 (g) + Q Solution: a) Pressure changeshifts the equilibrium of reactions involving gaseous substances (g). Let us determine the volumes of gaseous substances before and after the reaction by stoichiometric coefficients:On the principle of Le Chatelier,with increasing pressure, balance shiftsin the direction of the formation of substances occupying a smaller volume, therefore, the equilibrium will shift to the right, i.e. towards the formation of CO 2 , towards the direct reaction(→) . b) According to Le Chatelier's principle,when the temperature rises, the balance shiftstowards the endothermic reaction (- Q ), i.e. in the direction of the reverse reaction - the reaction of decomposition of CO 2 (←) since on the law of conservation of energy: Q- 2 CO (g) + O 2 (g) ↔ 2 CO 2 (g) + Qv) With increasing oxygen concentrationthe equilibrium of the system is shiftingtowards obtaining CO 2 (→) since an increase in the concentration of reagents (liquid or gaseous) displaces towards the products, i.e. towards a direct reaction. 4. Homework. A.14, Complete the task in pairsExample 1. How many times will the speed of the forward and reverse reactions in the system change: 2 SO 2 (g) + O 2 (g) = 2 SO 3 (g) if the volume of the gas mixture is reduced by three times? In which direction will the equilibrium of the system shift?Solution. Let's designate the concentration of reactants: [ SO 2] = a, [About 2] = b, [SO 3] = with. According to the law of action of masses, the velocityv direct and reverse reactions before volume change:v pr = Ka 2 b v arr = TO 1 with 2 . After reducing the volume of the homogeneous system by three times, the concentration of each of the reacting substances will increase three times: [ SO 2 ] = 3 a , [O 2 ] = 3 b; [ SO 3 ] = 3 with ... At new concentrations of speed v’ forward and backward reaction:v’ NS = TO (3 a ) 2 (3 b) = 27 Ka 2 bv’ arr = TO 1 (3 with ) 2 = 9 TO 1 with 2 Hence:

Consequently, the speed of the forward reaction increased by 27 times, and the reverse - only nine times. The equilibrium of the system has shifted towards education SO 3 . Example 2. Calculate how many times the rate of the reaction proceeding in the gas phase will increase when the temperature rises from 30 to 70 O C if the temperature coefficient of reaction is 2.Solution. The dependence of the rate of a chemical reaction on temperature is determined by the Van't Hoff rule of thumb according to the formula:Therefore, the reaction rate νТ 2 at a temperature of 70 O With more reaction speed νТ 1 at a temperature of 30 O C 16 times.Example 3. Equilibrium constant of a homogeneous system:CO (g) + H 2 O (g) = CO 2 (d) + H 2 (G)at 850 O С is equal to 1. Calculate the concentrations of all substances at equilibrium if the initial concentrations are: [СО] ref = 3 mol / l, [H 2 O] ref = 2 mol / l.Solution. In equilibrium, the rates of direct and reverse reactions are equal, and the ratio of the constants of these rates is constant and is called the equilibrium constant of the given system:v pr = TO 1 [DREAM 2 O]v arr = K 2 [CO 2 ] [N 2 ]
In the condition of the problem, the initial concentrations are given, while in the expression TO R only equilibrium concentrations of all substances in the system are included. Suppose that by the moment of equilibrium concentration [СО 2 ] R = NS mol / l. According to the equation of the system, the number of moles of the formed hydrogen will also be NS mol / l. The same number of moles (NS mol / l) CO and H 2 O is spent for education on NS moles of CO 2 and H 2 ... Therefore, the equilibrium concentrations of all four substances are:[CO 2 ] R = [H 2 ] R = NS mol / l; [CO] R = (3 – NS ) mol / l;[N 2 O] R = (2 – NS ) mol / L.Knowing the equilibrium constant, we find the value NS , and then the initial concentrations of all substances:

Thus, the sought equilibrium concentrations are:[CO 2 ] R = 1.2 mol / l;[N 2 ] R = 1.2 mol / l;[CO] R = 3 - 1.2 = 1.8 mol / l;[N 2 O] R = 2 - 1.2 = 0.8 mol / l.
Loading ...Loading ...