Give examples of reactions, an increase or decrease in the rate of which has a positive or negative meaning at work or at home. Please explain.
Answers:
Corrosion of metals: occurs both chemically and electrochemically in various industrial plants. Need to get rid of corrosion iron pipes by adding alloying elements, varnishes, paints, etc. Make it the best)))
Similar questions
- Please help me, write what visual and artistic means are there in the prose “The Last Date” by Turgenev, with examples =)
- Find 1 fraction 2 from 1t; 1 fraction 5 from 1t; 1 fraction 10 from 1 kg
- why didn't all your actions bring you pleasure?
- Express 305.702kg in centners and kilograms
- In the parallelogram KMNP, the bisector of the angle MKP is drawn, which intersects the side MN at point E. a) prove that the triangle KME is isosceles. b) Find the side KR if ME = 10 cm, and the perimeter of the parallelogram is 52 cm.
- 1. To melt 2 kg of copper taken at the melting temperature, 420 kJ of heat was required. Determine the specific heat of fusion of copper.
- A pair of lines from M. Yu. Lermontov's poem "Mtsyri" are given. In which example are rhyming words in different cases?
- A) You can’t hear the singing at a late hour / The monks praying for us. B) I saw mountain ranges, / Bizarre, like dreams... C) All this in a vague series / Suddenly ran before me. D) The snake slid between the stones; / But fear did not squeeze my soul... D) But I argued in vain with fate: / She laughed at me!
Chemical reaction. Reaction speed and factors on which it depends. Chemistry lesson. Methodological development intended for 1st year students.
Lesson type: lesson - introduction to new material.
Subject: Chemical reaction. Reaction speed and factors on which it depends.
Target: generalize and deepen knowledge about the rate of chemical reactions and the factors influencing it.
Tasks:
Educational objective:
Developmental tasks
Equipment: TV, VCR, film clip.
Candle, zinc, solutions of hydrochloric and sulfuric acids.
Lesson plan:
Organizing time.
Topic and purpose.
Motivation.
Updating.
Main part.
Conclusion.
Consolidation.
Lesson summary.
Homework.
During the classes:
1. Organizing time.
2. Topic and purpose. Write it down in your notebook.
3. Motivation.
Teacher: “What do we mean when we say the word SPEED?”
Studying:
Teacher: “At what speed can you eat candy? Cutlets?
How fast can you go shopping? Knit socks? Saw boards?
That is, SPEED is the change in a parameter per unit of time. (Write on the board)
Teacher: Is it possible to talk about the speed of a chemical reaction?
Students: give examples of various chemical processes.
4. Updating.
Teacher: Let's return to the topic of the lesson. What is a chemical reaction?
Message “Physical and chemical phenomena”.
Oral frontal work.
Surovtseva R. P., pp. 8, work No. 8. Option 1. (A, B, C, D - work in groups)
5. Main part.
Teacher: Do all chemical processes proceed at the same speed?
PROBLEM: What factors determine the rate of a chemical reaction? (WRITE ON THE BOARD)
Step by step solution to the problem:
1.What is the speed of a chemical reaction called? (p. 33, read and write down the definition in your notebook).
2.Teacher: So, speed chemical reactions vary greatly.
Some reactions need to be slowed down (rusting, oxidation), some need to be accelerated (obtaining medicines, other useful products).
REPEATING THE SAFETY RULES WHEN WORKING WITH REAGENTS!!!
3. Experiment No. 1. Film fragment. 6 min.
(The rate of a chemical reaction depends on the nature of the reactants.)
4. Experience No. 2. Burning a candle in air and under a hood.
(For dissolved substances and gases, the rate of a chemical reaction depends on the concentration of the reactants.)
5. Experiment No. 3. Place zinc granules in one test tube, and powder in another. Pour 2 ml of dilute hydrochloric acid into both test tubes.
(For substances in the solid state, the reaction rate is directly proportional to the surface area of the reacting substances.)
6. Experiment No. 4. Place two pieces of zinc in two test tubes. Pour 2 ml of dilute sulfuric acid into both test tubes. Warm one test tube slightly, leave the second for comparison. Oxygen begins to react with many substances at a noticeable speed already at room temperature (slow oxidation). As the temperature rises, a violent reaction begins and the reaction rate increases sharply.
(As the temperature increases, the rate of most reactions increases.)
6. CONCLUSION: The answer to the problematic question. Read page 34. Conditions affecting the rate of a chemical reaction.
Write down: CATALYSTS AND INHIBITORS.
7. Consolidation.
*Write down the reaction equations.
*Give examples of reactions, an increase or decrease in the speed of which has a positive or negative meaning in production or in everyday life.
8. Lesson summary. Ratings.
Introspection.
Lesson type: lesson introducing new material.
Goal: introduction of new concepts of inorganic chemistry: the rate of a chemical reaction, factors influencing the rate of a chemical reaction.
In this lesson, the peculiarities of the rate of a chemical reaction and the factors influencing the rate of a chemical reaction are clarified. Subsequent lessons will cover the processes of chemical production of sulfur and nitric acids, i.e., the material will be based on this lesson.
The specificity of this lesson is that students are introduced to the concept of the rate of a chemical reaction for the first time.
This lesson is 3 in the topic “Fundamentals of Theoretical Chemistry”.
The main task of this section is to formulate the concept of the basic laws of the flow of chemical reactions.
The level of development of mental operations in students of this group does not correspond to the socio-psychological standard. High level no one has. In order to develop the ability to draw analogies and generalize, when planning a lesson, I decided to use a problem-based method to study the main material of the lesson.
The following tasks were solved in this lesson:
Educational objective: expand and deepen knowledge chemical kinetics.
Developmental tasks: improve students’ abilities to analyze, compare, and draw conclusions.
Educational tasks: continue the formation of ideological concepts: about the knowability of nature, the cause-and-effect relationship between composition and properties.
Because this lesson third in the topic, the following lesson structure was chosen:
A few minutes are allocated for updating;
Most of the time is allocated to learning new material;
The remaining time is spent on consolidation.
The main emphasis of the lesson was on identifying the factors that influence the rate of a chemical reaction.
The following methods were used in the lesson: explanatory-illustrative, reproductive methods. To reveal the main material, a problematic method was chosen. The content of this topic allows us to construct it as a system of cognitive problems and conduct study, constantly involving students in the search for answers to certain questions.
Selected forms of training: frontal, group, individual.
The frontal form of work is used when solving basic cognitive problems in order to intensify the work of each student, develop the ability to draw analogies, and generalize the material.
Individual and group forms of work are used at the actualization stage, since already familiar material is repeated.
Control over the acquisition of knowledge, skills and abilities was carried out at various stages of the lesson various forms and methods:
*at the update stage - individual survey;
*at the stage of learning new material - visually, individually, frontally.
*individual control was carried out at the stage of knowledge consolidation.
During the lesson, TV, VCR, and film clips were used as teaching aids.
The high performance of students in the lesson was supported by the problematic presentation of the material (at the main stage of the lesson), the use of technical teaching aids, and work in groups.
I tried to maintain the psychological atmosphere with a friendly attitude towards students. I tried to leave my problems outside the classroom.
Chemical processes.
Production of sulfuric acid.
Rust formation.
Blackening of silver.
Food oxidation.
Receiving medications.
Souring of milk.
Protein rotting.
Sauerkraut.
Laundry.
Cooking food.
Burning candle.
2.Formation of rust.
3. Blackening of silver.
5. Obtaining medications.
6. Souring of milk.
7. Protein decay.
8. Sauerkraut.
9. Washing clothes.
10.Cooking.
11.Candle burning.
12.Combustion of gasoline in the engine
1.Production of sulfuric acid.
2.Formation of rust.
3. Blackening of silver.
4.Oxidation of food.
5. Obtaining medications.
6. Souring of milk.
7. Protein decay.
8. Sauerkraut.
9. Washing clothes.
10.Cooking.
11.Candle burning.
12.Combustion of gasoline in the engine
1.Production of sulfuric acid.
2.Formation of rust.
3. Blackening of silver.
4.Oxidation of food.
5. Obtaining medications.
6. Souring of milk.
7. Protein decay.
8. Sauerkraut.
9. Washing clothes.
10.Cooking.
11.Candle burning.
12.Combustion of gasoline in the engine
1.Production of sulfuric acid.
2.Formation of rust.
3. Blackening of silver.
4.Oxidation of food.
5. Obtaining medications.
6. Souring of milk.
7. Protein decay.
8. Sauerkraut.
9. Washing clothes.
10.Cooking.
11.Candle burning.
12.Combustion of gasoline in the engine
1.Production of sulfuric acid.
2.Formation of rust.
3. Blackening of silver.
4.Oxidation of food.
5. Obtaining medications.
6. Souring of milk.
7. Protein decay.
8. Sauerkraut.
9. Washing clothes.
10.Cooking.
11.Candle burning.
12.Combustion of gasoline in the engine
Page 1
The slowdown of the reaction, of course, increases when a salt containing the same anion, for example lithium chloride, is introduced into the reaction medium.
The reaction slows down due to the fact that hydrogen, which is relatively weakly bound and, obviously, most suitable for the hydrogenation of 1-hexene, becomes less and less with increasing pH. Since the activation energy we determined does not change in the studied pH range, then, obviously, the decrease in catalyst activity with increasing pH is associated with a decrease in the pre-exponential factor in the Arrhenius equation. Thus, we can assume that with increasing pH during the hydrogenation of 1-hexene, the number of active sites on the surface of the Pt catalyst decreases.
The slowdown of the reaction over time is associated with an increase in the value of recombination (destruction by mutual collision) of active centers, or with the appearance of a substance slowing down the process as one of the reaction products. The reaction is extremely sensitive to the slightest traces of foreign impurities. The latter can act in an accelerating manner (aldehydes, N02 85, etc.], organic peroxides [86, 87, etc.]) due to their ability to serve as the initial centers (or parts) of the reaction chain or to generate them. In other cases, impurities have an inhibitory effect on the reaction, depending on the fact that these negative catalysts, or so-called inhibitors, destroy active centers, for example, by reacting with them (or absorbing the energy of excited particles) and thus stopping the development of the reaction chain, cutting her off.
The slowdown of the reaction and the improvement in the quality of products, caused by the influence of an alkali metal and the limiting concentration of manganese, were studied using the example of the oxidation of paraffin with the participation of pyrolusite and alkaline arganese dioxide with the addition of a certain amount. It has been shown that the main inhibitory functions in the oxidation of hydrocarbons belong to alkali metal compounds.
Slowing down the reaction of No. 204 with toluene was achieved by filling the tubes with stainless steel shavings, diluting the reaction mixture C14 and reducing the amount of N204 to 1 7 - 1 mol per 1 mol of toluene. Acceleration of the nitration reaction into the core was achieved by adding 0 27 - 0 4 moles of acetic anhydride per 1 mole of toluene to the reaction mixture, and 2 5 - 3% 2 4 6-trinitrotoluene and up to 30% nitrotoluenes were obtained. Once formed, mononitrotoluenes are no longer nitrated. When toluene is nitrated into the nucleus, only mono- and trinitrotoluenes are obtained without the intermediate formation of dinitrotoluene. The exchange of anhydride with acetic acid does not accelerate the reaction.
The slowdown of the reaction due to structural changes can be so significant that the process of disproportionation of the four- or pentavalent ion is more advantageous, rather than the process of direct interaction of these ions with the reagents.
The slowdown in the reaction can be explained by the fact that the chloride complex T1 (III) is less reactive than the T13 or T1OH2 ions, but the reasons for the increase in the reaction rate in the region of higher concentrations of the C1 - - - ion are not clear.
Lukasevich explains the slowdown of the reaction in primary and secondary alcohols by the fact that in these alcohols there is hydrogen at the a-carbon atom, which breaks off in the form of a radical, which prevents the development of the chain. Taking the position of the free radical mechanism of reduction with formic acid, Lukasevich comes to the conclusion that sodium formate accelerates the reduction of Schiff bases by preventing their decomposition.
The slowdown of the reaction at elevated temperatures can be explained by a decrease in the activity of phosphoric acid due to the increase in the solubility of monocalcium phosphate in it, and the slowdown of the reaction at low temperatures by the fact that phosphoric acid, the concentration of which in the liquid phase of superphosphate is about 45% PzOsr, becomes more viscous and inactive.
The slowdown of the reaction in the SDS solution is consistent with the distribution coefficient 2 of 4-dinitro-fluorobenzene, which is predominantly localized in the micellar phase, while the nucleophilic agent glycylglycine is not solubilized by micelles. The effect of SDS can be explained based on the decrease in reactivity in the micellar phase and the redistribution of reagents.
The slowing down of the reaction with KOH when replacing the n-hydrogen with a p-mstoxy group probably depends on the fact that substitution and elimination were studied in the MSSM.
| Polycondensation of decamethylene glycol with adipic acid, catalyzed by i-toluenesulfonic acid (0 1 equivalent. % at various temperatures. Dependence of the average degree of polymerization on the reaction duration. |
The slowing down of the reaction by alkyl substituents is therefore due to a decrease in the entropy of activation.
Slow response due to deficiency free water, can be easily prevented by increasing the diffusion rate of CS2 by vigorous stirring or mechanical disruption of the fiber structure, so that the reaction can be completed 10 times faster.
Slowing down the reaction of N204 with toluene was achieved by filling the tubes with stainless steel shavings, diluting the reaction mixture with CC14 and reducing the amount of N204 to 1 7 - 1 mol per 1 mol of toluene. Acceleration of the nitration reaction into the core was achieved by adding 0 27 - 0 4 moles of acetic anhydride per 1 mole of toluene to the reaction mixture, and 2 5 - 3% 2 4 6-trinitrotoluene and up to 30% nitrotoluenes were obtained. The resulting mononitrotoluenes are not nitrated further. When toluene is nitrated into the core, only mono- and trinitrotoluenes are obtained without the intermediate formation of dinitrotoluene. Replacing the anhydride with acetic acid does not speed up the reaction.
Objectives: deepen and generalize knowledge about the rate of chemical reactions; dependence of the rate of homogeneous and heterogeneous reactions on various factors; be able to experimentally confirm the influence of individual factors on the rate of chemical reactions. Continue the formation of such logical techniques as observation, analysis, comparison and generalization. Promote learning of specific teamwork skills.
Questions for students: 1. Give examples of reactions, the increase or decrease in speed of which has a positive or negative meaning in production, in everyday life or in nature. 2. How is the speed of chemical reactions measured in contrast to speed in mechanics? 3. How does the rate of a chemical reaction change over time if you do not interfere with its course? 4. What is concentration, why do they put the sign (-) in front of the formula, for which reactions is the formula correct? Define homogeneous and heterogeneous reaction? Give examples. Stage 1.
Stage 2. Research in groups. Group 1 studies the influence of the nature of the reacting substances. Group 2: influence of concentration. 3rd group - influence of temperature. Group 4 studies the effect of a catalyst on the rate of a chemical reaction. Group 5: the influence of the surface area of reacting substances on the rate of a heterogeneous chemical reaction. Repeat safety rules!!!
Factors influencing the rate of a chemical reaction. Examples and signs of a chemical reaction. Conclusions about the conditions affecting the rate of a chemical reaction. Nature of the reactants Mg + HCl MgCl 2 +H 2 Rapid gas evolution. Fe + HCl FeCl 2 + H 2 Slow gas evolution The more active the metal, the faster the reaction occurs. Concentration Zn+ HCl (1:1) ZnCl 2 +H 2 Rapid gas release Zn+ HCl (1:5) ZnCl 2 +H 2 Slow gas release The higher the concentration, the faster the reaction. Temperature Heating Zn+ HCl ZnCl 2 +H 2 Rapid gas evolution. without Heating Zn+ HCl ZnCl 2 +H 2 Slow gas evolution. Catalysts MnO 2 H 2 O 2 H 2 O+O 2 fast Without catalyst; H 2 O 2 H 2 O+O 2 slowly The higher the temperature, the faster the reaction occurs. In the presence of a catalyst, the reaction proceeds faster.
Factors influencing the rate of a chemical reaction. Examples and signs of a chemical reaction. Conclusions about the conditions affecting the rate of a chemical reaction. Contact area of reacting substances. Zn (powder) +HCl ZnCl 2 +H 2 Rapid gas release Zn (granule) +HCl ZnCl 2 +H 2 Slow gas release The larger the contact area of the reacting substances, the faster the reaction proceeds.
Stage 4 discussion of the importance of studying the kinetics of chemical reactions. 1.Why do substances burn faster in oxygen than in air? 2. Why are perishable foods stored in the refrigerator? 3. Explain the working principle of a pressure cooker. 4. How can we explain that in order to decompose sucrose in a test tube, the acidified solution must be boiled, but in the digestive tract the same process occurs at a temperature of 37 degrees and much faster? 5. What products does it produce? chemical industry, which is obtained based on the use of catalysts? 6. Why do we need knowledge about the rate of a chemical reaction?
Chemical reaction rate- change in the amount of one of the reacting substances per unit of time in a unit of reaction space.
The speed of a chemical reaction is influenced by the following factors:
- the nature of the reacting substances;
- concentration of reactants;
- contact surface of reacting substances (in heterogeneous reactions);
- temperature;
- action of catalysts.
Active collision theory allows us to explain the influence of certain factors on the rate of a chemical reaction. The main provisions of this theory:
- Reactions occur when particles of reactants that have a certain energy collide.
- The more reactant particles there are, the closer they are to each other, 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. To do this, the particles must have sufficient energy.
- The minimum excess energy required for effective collision of reactant particles is called activation energy Ea.
- The activity of chemicals is manifested in the low activation energy of reactions involving them. The lower the activation energy, the higher the reaction rate. For example, in reactions between cations and anions, the activation energy is very low, so such reactions occur almost instantly
The influence of the concentration of reactants on the reaction rate
As the concentration of reactants increases, the reaction rate increases. In order for a reaction to occur, two chemical particles must come together, so the rate of the reaction depends on the number of collisions between them. An increase in the number of particles in a given volume leads to more frequent collisions and an increase in the reaction rate.
An increase in the rate of reaction occurring in the gas phase will result from an increase in pressure or a decrease in the volume occupied by the mixture.
Based on experimental data in 1867, Norwegian scientists K. Guldberg and P. Waage, and independently of them in 1865, Russian scientist N.I. Beketov formulated the basic law of chemical kinetics, establishing dependence of the reaction rate on the concentrations of the reactants -
Law of mass action (LMA):
The rate of a chemical reaction is proportional to the product of the concentrations of the reacting substances, taken in powers equal to their coefficients in the reaction equation. (“effective mass” is a synonym modern concept"concentration")
aA +bB =cС +dD, Where k– reaction rate constant
ZDM is performed only for elementary chemical reactions occurring in one stage. If a reaction proceeds sequentially through several stages, then the total speed of the entire process is determined by its slowest part.
Expressions for the rates of various types of reactions
ZDM refers to homogeneous reactions. If the reaction is heterogeneous (reagents are in different states of aggregation), then the ZDM equation includes only liquid or only gaseous reagents, and solid ones are excluded, affecting only the rate constant k.
Molecularity of the reaction is the minimum number of molecules involved in an elementary chemical process. Based on molecularity, elementary chemical reactions are divided into molecular (A →) and bimolecular (A + B →); trimolecular reactions are extremely rare.
Rate of heterogeneous reactions
- Depends on surface area of contact between substances, i.e. on the degree of grinding of substances and the completeness of mixing of reagents.
- An example is wood burning. A whole log burns relatively slowly in air. If you increase the surface of contact between wood and air, splitting the log into chips, the burning rate will increase.
- Pyrophoric iron is poured onto a sheet of filter paper. During the fall, the iron particles become hot and set fire to the paper.
Effect of temperature on reaction rate
In the 19th century, the Dutch scientist Van't Hoff experimentally discovered that with an increase in temperature by 10 o C, the rates of many reactions increase by 2-4 times.
Van't Hoff's rule
For every 10 ◦ C increase in temperature, the reaction rate increases by 2-4 times.
Here γ (Greek letter "gamma") - the so-called temperature coefficient or van't Hoff coefficient, takes values from 2 to 4.
For each specific reaction, the temperature coefficient is determined experimentally. It shows exactly how many times the rate of a given chemical reaction (and its rate constant) increases with every 10 degree increase in temperature.
Van't Hoff's rule is used to approximate the change in the reaction rate constant with increasing or decreasing temperature. A more precise relationship between the rate constant and temperature was established by the Swedish chemist Svante Arrhenius:
How more E a specific reaction, so less(at a given temperature) will be the rate constant k (and rate) of this reaction. An increase in T leads to an increase in the rate constant, this is explained by the fact that an increase in temperature leads to a rapid increase in the number of “energetic” molecules capable of overcoming the activation barrier Ea.
Effect of catalyst on reaction rate
You can change the rate of a reaction by using special substances that change the reaction mechanism and direct it along an energetically more favorable path with a lower activation energy.
Catalysts- these are substances that participate in a chemical reaction and increase its speed, but at the end of the reaction they remain unchanged qualitatively and quantitatively.
Inhibitors– substances that slow down chemical reactions.
Changing the rate of a chemical reaction or its direction using a catalyst is called catalysis .
