An open lesson in the discipline "chemistry" on the topic "rate of chemical reactions." Lesson "The rate of a chemical reaction. Factors influencing the rate of a chemical reaction" The rate of a chemical reaction lesson
O.I. Ivanova, chemistry teacher, MBOU “Napolnokotyakskaya Secondary School”, Kanashsky district of the Chechen Republic
Lesson "Factors influencing the rate of a chemical reaction"
Objective of the lesson: study of factors influencing the rate of a chemical reaction
Tasks:
find out what factors affect speed chemical reactions
teach to explain the influence of each factor;
stimulate students' cognitive activity by creating problematic situation;
to form the competencies of schoolchildren (educational, cognitive, communicative, health);
improve practical skills students.
Lesson type: problem-dialogical.
Forms of work: group, individual.
Equipment and reagents: set of test tubes, test tube holder, stand, alcohol lamp, 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.
Lesson progress:
1st stage:
Call: Hello guys! Today we will introduce ourselves as research scientists. But before we start learning new material, I would like to demonstrate a small experiment. Please look at the board and make your guesses about the course of these reactions:
A) copper and iron sulfate;
B) solution of copper sulfate and potassium hydroxide
Will these reactions take place? Please go to the board and write the equations for these reactions.
Let's look at these examples (the teacher conducts the experiment).
There are two test tubes on the table, both contain a solution of copper sulfate, but one test tube contains added sodium chloride; we drop an aluminum granule into both test tubes. What are we observing?
PROBLEM: Why in the second case do we not see signs of a reaction? Are our assumptions really wrong?
CONCLUSION: Chemical reactions occur at different rates. Some progress slowly, over months, such as the corrosion of iron or the fermentation of grape juice, which results in wine. Others are completed in a few weeks or days, such as the alcoholic fermentation of glucose. Still others end very quickly, such as the precipitation of insoluble salts, and some occur instantly, such as explosions.
Almost instantly, very quickly, many reactions occur in aqueous solutions: these are ionic reactions that occur with the formation of a precipitate, gas, or neutralization reaction.
Now let’s remember what you know about the speed of chemical reactions.
Understanding the concept. List the definition, formulas, and units 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 just listed? (Factors)
There are chemical instruments and reagents on the tables in front of you. For what purpose do you think you will conduct the 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 study in this lesson.
We write the name of the topic and the date in the notebooks.
IIstage:
UNDERSTANDING THE CONTENT.
What factors influence the rate of chemical reactions?
Students list: temperature, nature of reactants, concentration, contact surface, catalysts.
How can they change the rate of reaction?(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 collision theory. Its main idea is this: reactions occur when particles of reagents that have a certain energy collide. From this we can draw the following conclusions:
The more reactant particles there are, the more likely they are to collide and react.
Only effective collisions lead to a reaction, i.e. those in which “old connections” are destroyed or weakened and therefore “new ones” can be formed. But for this, the particles must have a certain energy.
The minimum excess energy required for effective collision of reactant particles is called activation energy (record the definition in notebooks).
Thus, in the path of all particles entering 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. When the energy barrier is large, additional energy is needed to overcome it; sometimes a “good push” is enough.
Let us turn to the statement of Leonardo da Vinci (Knowledge that has not been verified by experience is fruitless and full of errors).
Teacher: How do you understand the meaning of these words?(test theory with practice)
Yes, indeed, every theory must also be tested in practice. Next, you have to study for yourself. various factors on the speed of reactions. To do this, you will carry out reactions, guided by the instructions on your tables, and draw up a protocol for the experiment. After this, one student from the group will need to go to the board, explain the influence of which factor you considered, write equations on the board and draw a conclusion according to collision theory and activation theory.
TB instruction.
CARRYING OUT PRACTICAL WORK IN GROUPS
Card 1. Factors affecting the rate of a chemical reaction:
1. Nature of reactants.
Pour some sulfuric acid into two test tubes.
2. Lower into one small quantity magnesium, and in the other - a zinc granule.
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. What factor did you find out during this work?
6. Find in the laboratory report the half-reactions that correspond to your experiment and complete the reaction equations.
Card 2. Factors affecting the rate of a chemical reaction:
2. Concentration of reacting substances.
Be careful when working with 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 test tubes.
3. Place a zinc granule in each of the test tubes.
4. In which of the test tubes did the evolution of hydrogen begin faster?
Card 3. Factors affecting the rate of a chemical reaction:
3. Contact area of reacting substances.
Be careful when working with substances. Remember the safety rules.
1. Grind a small piece of chalk in a mortar.
2. Pour some sulfuric acid solution into two test tubes. Be very careful, pour only a little acid!
3. At the same time, place the powder in one test tube and a piece of chalk in the other.
4. In which test tube will the reaction take place faster?
5. What factor did you find out in this experiment?
6. How can this be explained from the point of view of collision theory?
7. Write the equation for the reaction.
Card 4. Factors affecting the rate of a chemical reaction:
4.Temperature.
Be careful when working with substances. Remember the safety rules.
1. Pour a solution of sulfuric acid into both test tubes and place a granule of copper oxide in them.
2. Gently heat one of the test tubes. First, we heat the test tube slightly at an angle, trying to warm it along its entire length, then only the lower part, having already straightened the test tube. Hold the test tube with a holder.
3. In which of the test tubes does the reaction proceed more intensely?
4. What factor did you find out in this experiment?
5. How can this be explained from the point of view of collision theory?
6. Write the equation for the reaction.
Card 5. Factors affecting the rate of a chemical reaction:
5. Availability of special catalyst substances, substances that increase the rate of a chemical reaction.
Be careful when working with substances. Remember the safety rules.
Pour hydrogen peroxide into two glasses.
Carefully sprinkle a few crystals of potassium dichromate into one of the test tubes. Stir the resulting solution with a glass rod.
Light a sparkle and then extinguish it. Bring the smoldering splinter to the solutions in both glasses as close to the solution as possible, but without touching the liquid. The splinter should light up.
In which of the test tubes is rapid gas evolution observed? What gas is this?
What role does potassium dichromate play in this reaction?
What factor did you find out in this experiment?
Write the reaction equation.
DISCUSSION OF THE RESULTS OBTAINED.
For discussion, one student from each working group comes to the board (one at a time)
Drawing up a summary protocol of laboratory work based on answers to the questions of the workshop.
Write reaction equations on the board and draw appropriate conclusions. All other students record their conclusions and equations in the protocols.
Influence of the nature of the reactants
Problem:
Teacher: mass of substances taken, weighed portions of solids, concentration hydrochloric acid, the reaction conditions are the same, but the intensity of the processes taking place (the rate of hydrogen evolution) is different?
Discussion:
Students: we took different metals.
Teacher: All substances are made up of atoms of chemical elements. How are they different? chemical elements according to your knowledge periodic law and the Periodic Table of D.I. Mendeleev?
Students: Serial number, position in Periodic table D.I. Mendeleev, that is, they have different electronic structure, and therefore simple substances formed by these atoms have different properties.
Teacher: that is, these substances are of different nature. Thus, the rate of a chemical reaction will depend on the nature of a particular reactant, since they have different structures and properties.
Conclusion:
Students: The rate of a chemical reaction will depend on the nature of the reactants: 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 of the experiment are the same, but the intensity of the processes taking place (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 we added water, we changed (reduced) the concentration of sulfuric acid in one test tube, and the intensity of hydrogen evolution decreased.
Conclusion:
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.
Teacher's explanation: CONCENTRATION OF REACTING SUBSTANCES.
The more reactant particles there are, the closer they are to each other, the more likely they are to collide and react. Based on large experimental material in 1867. Norwegian scientists K. Guldberg and P. Waage and, independently of them, in 1865 the Russian scientist N.I. Beketov formulated the basic law of chemical kinetics, establishing the dependence of the reaction rate on the concentrations of the reacting substances:
The reaction rate is proportional to the product of the concentrations of the reacting substances, taken in powers equal to their coefficients in the reaction equation.
This law is also called by law active masses. It is valid only for gaseous and liquid substances!
2A+3B=A2B3 V=k*CA2*.CB3
Task 1. Write kinetic equations for following reactions:
Task 2.
How will the rate of a reaction with the kinetic equation change?
v= kCA2CB, if the concentration of substance A is increased by 3 times.
Dependence on the surface area of reacting substances
Problem:
Teacher: all substances are identical in their chemical nature, identical in mass and concentration, react at the same temperature, but the intensity of hydrogen evolution (and therefore the rate) is different.
Discussion:
Students: A piece of chalk and chalk powder of the same mass have different occupied volumes in a test tube, varying degrees grinding. Where this degree of grinding is greatest, the rate of hydrogen evolution is maximum.
Teacher: this characteristic is the surface area of contact of the reacting substances. In our case, the surface area of contact between calcium carbonate and H2SO4 solution is different.
Conclusion:
Students: The rate of a chemical reaction depends on the area of contact of the reacting substances: than larger area contact of reacting substances (degree of grinding), the greater the reaction rate.
Teacher: such a dependence is not always observed: for some heterogeneous reactions, for example, in the Solid - Gas system, at very high temperatures(more than 500 0C), highly crushed (to powder) substances are capable of sintering, thereby reducing the surface area of contact of the reacting substances.
Effect of temperature
Problem:
Teacher: The substances taken for the experiment are of the same nature, the mass of the CuO powder taken and the concentration of sulfuric acid are also the same, but the reaction rate is different.
Discussion:
Students: This means that when we change the reaction temperature, we also change its speed.
Teacher: Does this mean that as the temperature increases, the rate of all chemical reactions will increase?
Students: No. Some reactions occur at very low and even sub-zero temperatures.
Conclusion:
Students: Consequently, any change in temperature of a few degrees will significantly change the rate of the chemical reaction.
Teacher: This is practically what Van't Hoff's law sounds like, which will be in effect here: For every 10 ºC change in the reaction temperature, the rate of the chemical reaction changes (increases or decreases) by 2-4 times.
Teacher's explanation: TEMPERATURE
How higher temperature, the more active particles there are, 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:
For every 10° C increase in temperature total number collisions increase by only ~ 1.6%, and the reaction rate increases by 2-4 times (100-300%).
The number showing how many times the reaction rate increases when the temperature increases by 10° C is called the temperature coefficient.
Van't Hoff's rule is expressed mathematically by the following formula:
WhereV1 -reaction rate at temperaturet2 ,
V2 - reaction rate at temperaturet1 ,
y- temperature coefficient.
Solve the problem:
Determine how the rate of a certain reaction changes when the temperature increases from 10 to 500C. The reaction temperature coefficient is 3.
Solution:
Substitute these problems into the formula:
the reaction rate will increase 81 times.
Catalyst influence
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.
Conclusion:
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, absorption nutrients 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)
There once 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 half of the camels for yourself. You, middle son, have just begun to help me - take the third part for yourself. And you, youngest, 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 out into a large field, counted them, and it turned out that there were only seventeen camels in the herd. And it was impossible to divide them by 2, 3, or 9! No one knew what to do. The sons began to argue, and each offered his own solution. And they were already tired of arguing, but they never came to general decision.
At this time, a traveler was riding past on his camel. Hearing screaming and arguing, he asked, “What happened?”
And the sons told about their misfortune. The traveler got off the camel, let it into the herd and said: “Now divide the camels, as your father ordered.”
And since there were 18 camels, the eldest son took half, that is, 9, the middle son took a third, that is, 6 camels, and the youngest son took a ninth, that is, two camels. And when they divided the herd in this way, there was one more camel left in the field, because 9+6+2 equals 17.
And the traveler mounted his camel and rode on.
Laboratory work (protocol)
| Observations | |||
| Dependence of the reaction rate on the nature of the reactants Zn + H2SO4(10%)= Mg + H2SO4(10%)= | V 1 V 2 | ||
| 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 | ||
| Dependence of 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 K2Cr2O7 | V 1 V 2 |
REFLECTION.
What did we learn in this lesson?
Make a cluster on the topic “Factors influencing the speed of HR.”
Why do we need knowledge about the factors influencing the rate of chemical reactions?
Are they used in everyday life? If applicable, name the areas of application.
Test on the topic (5 minutes).
Test
1. The rate of a chemical reaction is characterized by:
1) the movement of molecules or ions of reacting substances relative to each other
2) the time during which the chemical reaction ends
3) the number of structural units of a substance that entered into a chemical reaction
4) change in the quantities of substances per unit time per unit volume
When the temperature of the reacting substances increases, 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
As the concentration of reactants increases, the rate of the chemical reaction:
1) decreases
2) increases
3) does not change
4) changes periodically
To increase the rate of a chemical reaction
2CuS(TV)+ 3O2
(G.) = 2CuO(TV.) + 2SO2
(G.)
+
Qnecessary:
1) increase the concentration of SO2
2) reduce SO2 concentration
3) reduce the temperature
4) increase the degree of grinding of CuS
Under normal conditionsWith lowest speed there is interaction between:
3) Zn and HCl (10% solution)
4) Mg and HCl (10% solution)
When the temperature increases from 10 to 30 °C, the reaction rate, the temperature coefficient of which = 3:
1) increases 3 times
2) increases by 9 times
3) decreases by 3 times
4) decreases by 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. 11th grade. Textbook for general education institutions. 11th edition, stereotypical. M.: Bustard, 2009.
For the reaction, substances were taken at a temperature of 400C, and then they were heated to 700C. How will the rate of a chemical reaction change if its temperature coefficient is 2?
How will the rate of the reaction proceeding according to the equation 2NO+O2=2NO2 change if the concentration of both substances is increased by 3 times?
RATE OF CHEMICAL REACTIONS 6.4.2 No. 86
Explanatory note.
This development training session refers to the section “Chemical transformations” studied in grade 11. During the preparation of the lesson on the topic, the general requirements to the formation of classes, such as the relationship between the principles of clarity, accessibility and scientific nature of the proposed material, adherence to a culture of safe handling of substances and instilling a holistic worldview of chemical phenomena and processes, forecasting and planning lesson results.
Clearly formulated goals and objectives of the lesson are realized using various methods, shapes and methodological techniques training. A lesson in discovering new knowledge with elements of research is proposed, since at this stage students will receive a sufficient number of theoretical concepts that are reinforced during the practical part of the lesson. The following forms of organization are used educational activities: frontal, group, individual. The teacher is assigned a role in regulating the learning process, guiding students, monitoring their observations, correcting and supplementing their results and analyzing the latter.
Planned results: form basic concepts on the topic, understand the significance of the influence of various factors on the rate of a chemical reaction. Understand the possibility of controlling a chemical reaction by changing the conditions of its occurrence. Develop the ability to plan and carry out a chemical experiment, skillfully recording the results, and analyze them. Recognize the integrity of ongoing chemical processes and phenomena, vary concepts as applied to phenomena in the environmental and interdisciplinary spheres.
Lesson topic : rate of chemical reactions.
Lesson Objectives : study the essence of the concept: the rate of chemical reactions, identify the dependence of this quantity on various external factors.
Lesson objectives:
educational What is the rate of chemical reactions and what factors does it depend on?
developing Students learn to process and analyze experimental data, identify the essence of a chemical reaction, find out the relationship between the rate of a chemical reaction and external factors
educational Students develop communication skills during the steam room, teamwork. They use the means of chemistry to understand the processes occurring in the surrounding world. During practical work understand the necessity of following instructions exactly to obtain results.
Lesson type : a lesson in discovering new knowledge with elements of exploration.
Teaching method : partially searchable, form of organization: individual, group, frontal, collective
Literature for teachers and students:
2. G.E.Rudzitis, F.G.Feldman Chemistry. 11th grade. Basic level/ Textbook for educational institutions.
3. Gara N.N. Chemistry lessons 11th grade.
4. Gara N.N., Gabruseva N.I. Chemistry. Problem book with “assistant” 11th grade.
Learning Tools: chemicals and equipment for experiments, multimedia console, computer.
Lesson steps | Justification of the teacher's activities | Predicted activities of students | Formed UUD |
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Mutual greetings between students and teachers; recording of absentees; checking students' readiness for the lesson. | Prepare students for work | Class readiness for work | Willingness to cooperate and co-create with the teacher |
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Let's remember:
| Lead students to consider the purpose and objectives of the lesson. Ensure students' motivation and acceptance of the lesson task When discussing question (2), it is necessary to emphasize that a chemical reaction is possible only when molecules collide | The active work of students shows their readiness to perceive the topic of the lesson From personal life experience, students assume that the duration of various reactions is different. | Be able to participate in a collective discussion and argue your position. Be able to use knowledge and everyday observations |
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We write down the topic of the lesson “Rate of chemical reactions.” Let us formulate the objective of the lesson: to find out what the rate of a chemical reaction is and what factors it depends on. During the lesson we will get acquainted with the theory of the question “rate of a chemical reaction”. Thenin practice we will confirm some of our theoretical assumptions. | State the purpose of the lesson and a rough plan for its implementation. | |||||||||||||||||||||||||
Let's look at two examples. On the table there are two test tubes, in one there is an alkali solution (NaOH), in the other there is a nail; pour CuSO solution into both test tubes 4. What do we see? In the first test tube the reaction occurred instantly, in the second there were no visible changes yet. Let’s create reaction equations (two students write the equations on the board):
Cu 2+ + 2OH - = Cu(OH) 2
Fe 0 + Cu 2+ = Fe 2+ + Cu 0 Note that reaction 1) is homogeneous, and reaction 2) is heterogeneous. This is important to us. How long does the reaction last and what does it depend on? We will try to answer these questions during our lesson. The study of the rates and mechanisms of chemical reactions is calledchemical kinetics. | It is necessary to confirm students’ assumptions with a chemical experiment. | Based on the results of the demonstration experiment, students are convinced of the validity of their assumptions | Be able to independently or with the help of a teacher record the results of a demonstration, draw conclusions, and plan a possible stage of study. Be able to write equations of chemical reactions. |
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Let's turn to the concept of “speed”. You know such combinations as movement speed, reading speed, pool filling speed, etc. In general, what is speed? Change of any factor per unit of time. And what factor changes when we're talking about about reaction speed? We have already said that a chemical reaction occurs when particles collide. Then, obviously, the faster the particles collide, the faster the reaction rate. When particles of the starting substances collide, new particles are formed - reaction products. What changes over time in a chemical reaction? The amount of starting materials changes and the amount of reaction products changes. If we refer the amount of a substance to a unit volume, we get the molar concentration of the substance. The molar concentration of a substance is measured in mol/l. To determine the rate of a reaction, it is necessary to have data on the change in the concentration of any component of the reaction at certain intervals. The reaction equation is written on the board I 2 (gas) + H 2 (gas) + 2HI (gas) and there is a table of changes in iodine concentration over time (the right column – the change in HI concentration has not yet been filled in) | Provide meaningful perception of knowledge Establish a factor by which one can judge the speed of a reaction Introduction to the concept of molar concentration and its units of measurement | Active actions of students with the object of study During the conversation, students come to the conclusion about the connection between the rate of reaction and the concentration of the substances involved in the reaction | Be able to build cause-and-effect relationships, carry out the required comparison, generalization and dependence. |
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We build a graph of changes in iodine concentration over time CHI, mol/l 3 1,2 1,0 2 1,0 0,8 0,8 0,6 0,6 0,4 3 0,4 0,2 0,2 0 5 10 15 20 Time, s | A graph of changes in the concentration of a reactant over time gives students the opportunity to independently determine the reaction rate and monitor how it changes during the reaction | Formation of research skills - building a graph based on experiment data | Be able to record the dependence of the reaction rate on various factors. Formulate appropriate conclusions |
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The curve of changes in the concentration of a reactant or reaction product over time is calledkinetic curve. Chemical reaction rateis the change in the concentration of one of the reactants per unit of time. C 2 - c 1 ∆c 0.3 - 1 v = = = = - 0.03 (mol/l s) T 2 – t 1 ∆t 20 – 0 It is generally accepted that the reaction rate is a positive value; the minus sign indicates that the concentration dependence function I 2 decreasing from time to time. It follows from the graph that over time, not only the concentration decreases, but also the reaction rate. Let's confirm this with calculations. Let us determine the speed for different sections of the kinetic curve: in section 1: v = 0.08 mol / (l s), in section 2: v = 0.035 mol/(l s), in section 3: v = 0.01 mol/ (l s) What conclusions follow from the analysis of the kinetic curve? – The concentration of the reactant decreases as the reaction proceeds. The reaction rate decreases over time. Obviously, "reaction speed" is average speed process in a certain period of time, that the shorter the period of time, the more precisely the meaning speed. Let's fill the right column of the table with the concentration values of the reaction product HI. When determining the values, we are guided by the reaction equation. We construct a kinetic curve relative to the reaction product, determine the reaction rates for sections of the curve 1, 2 and 3. We come to the conclusion that the speed along the HI component is twice that of the I component 2 . This can be predicted from the reaction equation. additional analysis of the kinetic curve showed us that
| Step-by-step analysis of the kinetic curve leads to a meaningful understanding of the material being studied and eliminates the formalism of knowledge Plotting a kinetic curve for the reaction product shows that the accumulation of the reaction product occurs gradually as the starting substances are consumed It is necessary to pay attention to the physical essence of the stoichiometric coefficients in the chemical reaction equation | Independently formulate the concept of “reaction speed” Independently calculate the speed for the entire kinetic curve and its individual sections. Students derive the reaction rate units themselves The results of the calculations obtained are analyzed. formulate conclusions | ||||||||||||||||||||||||
Poster on the board: The chemical reaction proceeds according to the scheme A + B = 2C 2A + B = 2C | Assess the correctness and awareness of mastering new educational material, identify and eliminate gaps and misconceptions | Fill out the table | Be able to apply acquired knowledge to solve simple tasks. Analyze the correctness of the sequence of actions. Be able to participate in problem discussions and express own opinion about the result obtained. |
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Problem: in which of the vessels of the same capacity does the reaction take place? high speed, if at the same time 10 g of hydrogen fluoride is formed in the first vessel, and 53 g of hydrogen iodide is formed in the second? | Consolidate acquired knowledge | Independent completion of tasks with mutual verification of the results of completion. | Be able to independently solve problems on the topic. Analyze the correctness of the task. |
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Let's summarize the main results. Let's formulate them and write them down in a notebook. | Develop the ability to summarize the information received and highlight the main thing | Independent formulation of conclusions. Identification of the general emotional and productive background of the lesson. | Be able to summarize and systematize the information received. Participate in discussions and be able to express your thoughts. |
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A multi-level task using cards is offered: 1) mandatory: §.12, 1-6 p. 62 2) in-depth: §. 12, z1-4 p.63 3) creative: Consider the reactions for producing sulfuric acid from pyrite from the point of view of the dependence of the rate of the chemical reaction on decomposition. factors. | Accompanying the recorded task with comments for various levels. | Selecting one of the task types for homework. Extraction necessary information and recording it in a diary. | Done correctly and with pleasure homework. |
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Objective of the lesson: contribute to the formation of the concept of the speed of a chemical reaction through the use of information and communication technology.
Lesson objectives:
- development essential knowledge homogeneous and heterogeneous systems, the influence on the reaction rate of the nature of the reactants, their concentration, temperature, catalyst;
- promote the formation of operational control skills and the ability to use a computer through working with slides;
- cultivating an attitude towards chemistry as one of the fundamental components of natural science and an element of universal human culture;
- mastering the skills to observe chemical phenomena, make calculations based on chemical formulas substances and equations of chemical reactions.
Material and technical base and equipment:
Multimedia projector, computer, iron wire, copper (II) chloride, zinc (granules), hydrochloric acid (1:10) and (1:3), copper (II) oxide, nitric acid, alcohol lamp, hydrogen peroxide, splinter, oxide manganese (IY), test tubes, glass rod.
Didactic support: slides, disk with the teaching program "Chemistry. 8th grade", signal cards.
Lesson type: learning new material.
Lesson epigraph:
"We are extremely lucky that we
We live in a century when it is still possible
make discoveries"
Lesson progress
| Lesson stage | Teacher activities | Student activity |
| 1. Indicative-motivational stage(initiation of a lesson, announcement of the topic, goals, tasks, initial notes) | Teacher:“Guys, how do you understand the word speed? When studying what subjects did you come across the concept of speed? Do you think this concept is applicable in a chemistry course? Which practical significance has knowledge of the concept of the rate of a chemical reaction? |
Students: answer questions, formulate tasks
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| 2. Operational research stage(students work in groups and individually to complete tasks) | Teacher: gives the concept of the speed of a chemical reaction, students work for 10 minutes with a teaching computer program, distributes instructions for performing laboratory work in pairs, time is given 15 minutes (see application) |
Students: write down the topic of the lesson in a notebook, then introductory word teachers working with the educational computer program: "Chemistry. 8th grade." Perform laboratory work according to instructions and keep notes in notebooks. |
| 3. The stage of primary consolidation in a generalizing conversation. | Teacher asks questions: What defines the concept of the rate of a chemical reaction? - What formula expresses the rate of a chemical reaction? Which chemical systems are they homogeneous and heterogeneous? What factors influence the rate of chemical reactions? What chemical reactions did you use to prove these points? What do the concepts have in common? speed movement and speed of chemical reactions? |
Students answer the teacher's questions. |
| 4. Reflective-evaluative stage(primary control: express survey) | The teacher conducts an express- poll: Is it true that: : is the rate of a chemical reaction determined by the change in the concentration of one of the reactants or one of the reaction products per unit time? : the rate of a chemical reaction is measured: mol/hp? :The rate of a chemical reaction does not depend on temperature? : Are reactions that occur between substances in a heterogeneous environment called heterogeneous? : For every 10° C increase in temperature, the reaction rate increases by 2-4 times? |
Students prepare signal cards. Green means yes red - "no" yellow - “I doubt it.” |
| 5. Setting homework. | Offered to students: 29, 30, 31, p. 128 exercise 1, p. 125 exercise 1, 5, | Students write down homework in a diary. |
| 6. Summing up. | Teacher sums up the lesson, conducts reflection: if the guys have completed the assigned tasks, raise a red card, if there are some questions left - green, if more than half have not been learned - yellow. Evaluates and comments on the work of the most active students | Students raise signal cards. |
The rate of a chemical reaction characterizes how quickly or slowly the transformation of substances occurs. Chemical kinetics studies the rates of chemical reactions. One of its most important tasks is to control the speed of reaction.
For a homogeneous reaction occurring in a constant volume, the reaction rate is equal to the change in the concentration of any of the substances participating in the reaction per unit time:
If the concentration decreases (C 2< С 1), то перед дробью ставят знак «минус», т. к. скорость не может иметь negative value.
1. Nature of reactants
For example, metals (sodium and potassium) react with the same substance - water - at different rates. Potassium reacts very vigorously with water, and the hydrogen released ignites in air (Fig. 2). Sodium reacts with water more calmly (Fig. 1).
Rice. 1. Reaction of sodium with water
Rice. 2. Interaction of potassium with water
2. Concentration of starting substances
The greater the concentration of substances, the greater the probability of collision of reacting substances, therefore, the greater the reaction rate.
3. Temperature
Many chemical processes accelerate with increasing temperature. For example, meat room temperature will spoil much faster than in the refrigerator; in countries with humid tropical climate Cars rust faster than in northern latitudes.
For example, if a little black copper(II) oxide powder is added to a sulfuric acid solution, no change will be observed. When the mixture is heated, the solution will turn blue.
4. Pressure
Pressure affects the reaction rate when the reaction occurs with the participation of gaseous substances. As the pressure increases, the reaction rate increases. This is due to the fact that as pressure increases, the distance between molecules decreases, therefore the probability of collisions between molecules, leading to the transformation of a substance, increases.
5. Surface area of contact of starting substances
How more degree grinding a solid, the greater the area of contact of the substance with the solution. This, in turn, affects the speed of the reaction. The greater the surface area of contact of the reacting substances, the greater the reaction rate.
6. Presence of a catalyst
The rate of chemical reactions may depend on the presence of certain substances.
Substances that accelerate a chemical reaction, but are not consumed in it themselves, are called catalysts.
If you mix aluminum powder with iodine powder, there will be no signs of a reaction. There is no reaction. But as soon as you add a catalyst - a drop of water - it starts violent reaction. Water, in this case, participates in the reaction, accelerating the transformation of substances, but is not consumed in it itself.
Rice. 3. Reaction of aluminum with iodine in the presence of water
It should be remembered that one catalyst can speed up one reaction, but not another. There are also reactions that occur quickly without a catalyst. Such reactions are called non-catalytic. For example, these are ion exchange reactions in solutions.
Some reactions, under certain conditions, can proceed in both the forward and reverse directions. For example, carbon dioxide when interacting with water, it forms carbonic acid, which, in turn, decomposes into carbon dioxide and water.
CO 2 + H 2 O ↔ H 2 CO 3
Such reactions are written with a reversibility sign and are called reversible.
If in a reversible reaction the rates of the forward and reverse reactions are equal, then this state is called chemical equilibrium.
References
1. Orzhekovsky P.A. Chemistry: 9th grade: general education. establishment / P.A. Orzhekovsky, L.M. Meshcheryakova, M.M. Shalashova. - M.: Astrel, 2013. (§14)
2. Rudzitis G.E. Chemistry: inorganic. chemistry. Organ. chemistry: textbook. for 9th grade. / G.E. Rudzitis, F.G. Feldman. - M.: Education, OJSC “Moscow Textbooks”, 2009. (§14)
3. Khomchenko I.D. Collection of problems and exercises in chemistry for high school. - M.: RIA “New Wave”: Publisher Umerenkov, 2008.
4. Encyclopedia for children. Volume 17. Chemistry / Chapter. ed. V.A. Volodin, Ved. scientific ed. I. Leenson. - M.: Avanta+, 2003. (p. 116-131)
1. Single collection of digital educational resources(video experiments on the topic) ().
2. Electronic version magazine "Chemistry and Life" ().
Homework
1. p. 99 No. 3-8 from the textbook P.A. Orzhekovsky “Chemistry: 9th grade” / P.A. Orzhekovsky, L.M. Meshcheryakova, M.M. Shalashova. - M.: Astrel, 2013.
2. Why do liquid gasoline and ethanol burn quietly, but the vapors of these substances explode when mixed with air?
3. What is a catalyst? How does a catalyst change the rate of a chemical reaction?
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