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CLASSIFICATION OF CHEMICAL REACTIONS ACCORDING TO PHASE (AGGREGATE STATE) CHEMICAL REACTIONS HOMOGENEOUS HETEROGENEOUS (reacting substances and reaction products are in the same phase) 2SO2(g) + O2(g)=2SO3(g) HCl(l)+NaOH(l)=NaCl (l)+H2O Feature: they occur throughout the entire volume of the reaction mixture (the reactants and reaction products are in different phases) S(solid)+O2(g)=SO2(g) Zn(solid)+2HCl(l)=ZnCl2( g)+H2(g) Feature: occur at the interface
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RATES OF REACTIONS Rate of homogeneous reaction Rate of heterogeneous reaction A (g) + B (g) = C (g) ∆V = V2-V1 ∆ t = t2-t1 V (hom) = ∆V /(∆ t * V) C = V / V (mol/l) V (gom) = ± ∆С/ ∆ t (mol/l*s) V (het) = ± ∆V /(S*∆ t) (mol/m^2*s)
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Factors influencing the rate of a chemical reaction Concentration A+B=C+D V=k[A]*[B] Nature of reactants Contact surface area temperature catalyst
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Problem 1 At some point in time, the concentration of chlorine in the vessel in which the reaction H2+Cl2=2HCl takes place was equal to 0.06 mol/l. After 5 sec. The chlorine concentration was 0.02 mol/l. What is the average rate of this reaction in the specified period of time? Given C1(Cl2)=0.06 mol/l C2(Cl2)=0.02 mol/l ∆ t = 5 sec V=? Solution H2+Cl2=2HCl V= -(C2 – C1)/ ∆ t = (0.02-0.06)/5 = = 0.008 (mol/l*s) Answer: V = 0.008 (mol/l*s)
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Problem 2 How will the rate of the reaction FeCl3+3KCNS=Fe(CNS)3+3KCl occur in an aqueous solution change when the reacting mixture is diluted by half with water? Given C(ions)< 2 раза V2/V1=? Решение Fe(3+) + 3CNS(-) = Fe(CNS)3 V =k*^3 пусть до разбавления: х = Y = ^3 В результате разбавления концентрация ионов уменьшается: x/2 = y/2 = V2/V1 = k*(x/2)*(y/2)^3 = 16 Ответ: V2/V1 = 16 ^3 – в степени 3
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Problem 3 How will the reaction rate change when the temperature increases from 55 to 100 ‘C, if the temperature coefficient of the rate of this reaction is 2.5? Given γ =2.5 t1= 55 ' t2 = 100 ' Vt2/Vt1=? Solution = 2.5*((100-55)/10) = =25^4.5 = (5/2)^9/9= 43.7 Answer: the reaction rate increases by 43.7 times
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Problem 4 When the temperature increases by 30°C, the rate of some reaction increases by 64 times. What is the temperature coefficient of the rate of this reaction? Given Vt2/Vt1=64 t2 = 30 ’ γ =? Solution = γ^3 64 = γ^3 γ = 4 Answer: The temperature coefficient of the reaction rate is 4.
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Test: consolidation of knowledge 1. To reduce the reaction rate it is necessary: a) increase the concentration of reacting substances b) introduce a catalyst into the system c) increase the temperature d) lower the temperature 2. The reaction proceeds at the highest speed: a) neutralization b) combustion of sulfur in the air in ) dissolution of magnesium in acid d) reduction of copper oxide with hydrogen 3. Specify a homogeneous reaction. a) CaO+H2O=Ca(OH)2 b) S+O2=SO2 c) 2CO+O2=2CO2 d) MgCO3 MgO+CO2 4. Indicate the heterogeneous reaction. a) 2CO+O2=2CO2 b) H2+Cl2=2HCl c) 2SO2+O2=2SO2 (cat V2O5) d) N2O+H2=N2+H2O 5. Mark which reaction is both homogeneous and catalytic. a) 2SO2+O2=2SO3 (NO2 cat) b) CaO+CO2=CaCO3 c) H2+Cl2=2HCl d) N2+3H2=2NH3 (Fe cat)
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Test: consolidation of knowledge 6. Indicate how the rate of the bimolecular gas reaction 2NO2=N2O4 will change when the concentration of NO2 increases three times. a) will increase by 3 times b) will decrease by 6 times c) will increase by 9 times d) will increase by 6 times 7. Indicate to which process the expression for the law of mass action for the rate of chemical reaction V=k^x corresponds. a) S+O2=SO2 b) 2H2+O2=2H2O c) 2CO+O2=2CO2 d) N2+O2=2NO 8. Note the rate of which process will not change if the pressure in the reaction vessel is increased (t unchanged). a) 2NO+O2=2NO2 b) H2+Cl2=2HCl c) CaO+H2O=Ca(OH)2 d) N2O4=2NO2 9. Calculate what the temperature coefficient of the reaction rate is, if when the temperature decreases by 40'C its the speed decreased by 81 times.
Chemical kinetics is one of the complex branches of chemistry. This presentation helps students master primary concepts, systematize more complex material and practice solving standard questions included in the Unified State Examination system.
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"C speed of chemical reactions." Lesson topic:
Chemical kinetics is a branch of chemistry that studies the rate and mechanism of chemical reactions.
Systems: Homogeneous (homogeneous) – systems in which the interface between the components is not visible. Gas mixtures, solutions. Heterogeneous (non-uniform) – systems in which the interface between the components is visible. TV in-in + tv. in-in, gas + TV. in-in, liquid + TV. in-in.
Reactions: Homogeneous - reactions occurring in homogeneous systems. They leak throughout the entire system. Heterogeneous – reactions occurring in heterogeneous systems. The phases flow at the interface.
The rate of a chemical reaction is the change in the concentration of one of the reacting substances per unit time per unit volume. + c 2 – c 1 + ∆c − t 2 – t 1 − ∆ t C – concentration, in mol / L t – time, in seconds = = MOL L ∙ C
Molar concentration - shows the number of moles of a substance present in 1 liter. C = n / V [C] = [mol/l]
Task 1. 1. A vessel with a volume of 5 liters contains 1 mole of hydrogen. Calculate the molar concentration of hydrogen. 2. A 2 liter solution contains 392 grams of sulfuric acid. Calculate the molar concentration of the solution.
Change in the concentration of the reactant over time С Concentration Time С 1 С 2 t 1 t 2 ∆ c ∆ t = ∆ c ∆ t
Factors affecting the rate of reaction 1. Concentration of reactants. 2.Temperature. 3. The nature of the reacting substances. 4. Contact area of reacting substances. 5. Catalyst.
The influence of the concentration of reactants on the reaction rate. The greater the concentration of reacting substances, the more often particles of substances collide, which means the reaction rate increases.
Law of mass action: the rate of a chemical reaction is proportional to the product of the concentrations of the reacting substances, taken to the power of stoichiometric coefficients. Guldberg, Waage, 1867
m A + nB = A m B n = k ٠ С А m ٠ C B n k – reaction rate constant: k = , with с А = с в = 1 mol/l with с А ٠ с в = 1 mol/l k – depends on the nature of the reactants and on t
Write down the ZDM expression for the reactions: 2CO + O 2 = 2CO 2 N 2 + 3H 2 = 2NH 3 4P + 5O 2 = 2P 2 O 5 = k ٠ [ CO ] 2 ∙ [ O 2 ] = k ٠ ∙ 3 = k ٠ 5
Calculation problems: 2. How many times is it necessary to increase the pressure in the system: N 2 (g) + 3 H 2 (g) 2 NH 3 (g) in order to increase the rate of the direct reaction by 256 times? In the system: 4NH 3 (g) + 3O 2 (g) 2N 2 (g) + 6H 2 O (g), the ammonia concentration was increased from 0.3 mol/l to 0.6 mol/l, and the oxygen concentration was decreased from 0.4 mol/l to 0.1 mol/l. How did the reaction rate change?
Temperature. Van't Hoff's rule: for every 10 0 C increase in temperature, the rate of most reactions increases by 2 - 4 times. t 2 - t 1 10 - temperature coefficient, which shows how many times the reaction rate increases when t increases by 10 0 C. 2 = 1 ٠ -
Calculation problems: How will the rate of a certain reaction change when the temperature decreases from 30 0 C to 0 0 C if the temperature coefficient is 2? At a temperature of 20 0 C, the reaction rate is 2.7 mol/hp. What is the reaction rate at a temperature of 0 0 C if the temperature coefficient is 3?
The effect of temperature on the reaction rate. As the temperature rises, the speed of movement of particles increases, so they collide more often, which means the reaction rate increases.
The influence of the nature of reactants on the reaction rate. 2K+2H 2 O=2KON+H 2 2H 2 +O 2 =2H 2 O
The influence of the nature of reactants on the reaction rate. Ca+2H 2 O=Ca(OH) 2 +H 2
The influence of the nature of reactants on the reaction rate. The more active the substance, the faster the reaction rate with its participation.
Interaction of metals with acids Zn + 2HCl = ZnCl 2 + H 2 1 Fe + 2HCl = FeCl 2 + H 2 2 Cu + 2HCl = reaction is impossible 1 > 2 Zn is more active than Fe, and Cu is a low-active metal
The influence of the contact area of reacting substances on the reaction rate. 1. The rate of heterogeneous reactions depends on the area of contact of substances. 2. Heterogeneous reactions occur only at the interface of reacting substances. 3. Rate of heterogeneous reaction: ∆ n ∆ t ∙ S heterog. =
The influence of the contact area of reacting substances on the reaction rate. The larger the contact surface of substances, the greater the reaction rate.
The influence of the catalyst on the reaction rate. Catalysts are substances that change the rate of chemical reactions. Chemical reactions that occur with the participation of catalysts are called catalytic. The catalyst itself is not consumed in the reactions and is not included in the final products.
The influence of the catalyst on the reaction rate. C 12 H 22 O 11 + 12 O 2 = 12 CO 2 + 11 H 2 O
Mechanism of catalytic reactions For a reaction: A + B = AB Mechanism: The catalyst interacts with the starting substance: A + K = AK The intermediate compound interacts with another starting substance: AK + B = AB + K Total equation: A + B = AB
How do you need to change the conditions in the system: 2 SO 2 (g) + O 2 (g) 2 SO 3 (g) + Q, which is in equilibrium, in order to achieve the maximum concentration of sulfur (IV) oxide? How will the equilibrium in the system shift: 2 H 2 S (g) + SO 2 (g) 2 H 2 O (g) + 3 S (t) + Q if: a) increase the temperature; b) lower the pressure; c) introduce a catalyst; d) increase the concentration of hydrogen sulfide; e) reduce the concentration of sulfur oxide (IV).
Homework: 1. Learn theory and definitions. 2. In writing: O. page 31 No. 48 write down the ZDM expression for the reactions: 2 SO 2 + O 2 = 2SO 3 4NH 3 + 3O 2 = 2N 2 + 6H 2 O 4NH 3 + 5O 2 = 4NO + 6H 2 O 2H 2 O 2 = 2H 2 O + O 2 Fe 2 O 3 + 3H 2 = 2Fe + 3H 2 O
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Lecture plan 1. Chemical kinetics 2. Rate of chemical reactions 3. The influence of concentration on the rate of chemical reactions 4. The influence of temperature on the rate of chemical reactions 5. The influence of the nature of reactants on the rate of chemical reactions 6. The influence of contact area on the rate of heterogeneous reactions 7. The influence of a catalyst on the speed and path of chemical reactions 8. Catalysts in chemical production and biological objects
The essence of chemical reactions 1) The essence of chemical reactions boils down to the breaking of bonds in the starting substances and the formation of new bonds in the reaction products. 2) The total number of atoms of each chemical element before and after the reaction remains constant. 3) The formation of bonds occurs with the release of energy, and the breaking of bonds occurs with the absorption of energy.
For homogeneous reactions The rate of a chemical reaction is the change in the concentration of one of the reactants per unit time at a constant volume. c 2 – c 1 c t 2 – t 1 t s - change in concentration, mol/l t – change in time, s v = -= MOL L * S
Concentration of reactants Law of mass action (LMA): the rate of a chemical reaction is proportional to the product of the concentrations of the reactants. For the reaction: mA + nB = A m B n ZDM: v = k٠С А m ٠C B n k – reaction rate constant: k = v, with с А = с в = 1 mol/l or with с А ٠ с в = 1 mol/l k – depends on the nature of the reactants and on t
Temperature Van't Hoff's rule: for every 10 0 C change in temperature, the rate of most reactions changes by 2 - 4 times. t 2 – t 1 10 – temperature coefficient, which shows how many times the reaction rate changes when t changes by 10 0 C v 2 = v 1 ٠
Physical meaning of the temperature coefficient If the temperature coefficient is 3, this means that the reaction rate increases by 3 times when the temperature increases by 10 0 C. When the temperature increases by another 10 0 C, the reaction rate increases by 3 2 = 9 times.
Contact area of reacting substances The rate of heterogeneous reactions depends on the contact area of the substances. Heterogeneous reactions occur only at the interface of reacting substances. The rate of a heterogeneous reaction is expressed by the formula: t * S V heterog. = MOL m 2 * C
The influence of a catalyst on the chemical reaction path of butadiene-1,3 ethyl acetate acetaldehyde ethylene diethyl ether
Plan: Rate of a chemical reaction Heterogeneous and homogeneous reactions Dependence of the reaction rate on various factors: – Nature of the reacting substances – Concentration of the substances – Contact area of the substances – Temperature – Presence of catalysts or inhibitors
The rate of a reaction is determined by the change in the amount of substance per unit time. In unit V (for homogeneous) Per unit surface of contact of substances S (for heterogeneous) n is the change in the amount of substance (mol); t – time interval (s, min) - change in molar concentration;
Task on applying knowledge on “Rate of chemical reactions” A chemical reaction occurs 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 decreased to 0.74 mol/l. Determine: a) the average reaction rate for this period of time; b) concentration of substance B after 20 minutes.
Self-test. Given: C (A) 1 = 0.80 mol/l C (B) 1 = 1.00 mol/l C (A) 2 = 0.74 mol/l = 20 min Find. a) homogeneous =? b) C (B) 2 =? Solution: a) determination of the average reaction rate in a solution is carried out according to the formula: b) determination of the amounts of reacting substances: A + B = C According to the equation 1 mol 1 mol According to the condition 0.06 mol 0.06 mol Amounts of reacted substances. Therefore, C(B) 2 = C(B) 1 - C = 1.00 -0.06 = 0.94 mol/l Answer: homogeneous. = 0.003 mol/l C(B) 2 = 0.94 mol/l
Collision theory. The main idea of the theory: reactions occur when particles of reagents 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 the activation energy Ea. The magnitude of the activation energy of substances is a factor through which the influence of the nature of the reacting substances on the reaction rate is affected.
Factor under study Substances used Conclusion Nature of reacting substances HCl ac. acid +Zn +Zn V 1 > V 2 The more active the substance that reacts, the faster this reaction occurs. V 2 The more active the substance entering the reaction, the faster this reaction occurs."> V 2 The more active the substance entering the reaction, the faster this reaction occurs."> V 2 The more active the substance entering the reaction, the faster this reaction occurs reaction." title=" Factor under study Substances used conclusion Nature of the reacting substances HCl acetic acid + Zn + Zn V 1 > V 2 The more active the substance that reacts, the faster this reaction occurs."> title="Factor under study Substances used Conclusion Nature of reacting substances HCl ac. acid +Zn +Zn V 1 > V 2 The more active the substance that reacts, the faster this reaction occurs."> !}
2. Concentrations of reactants. Based on a large amount of experimental material, in 1867 the 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.
Law of mass action. Guldberg (). Norwegian physical chemist. P. Waage (). Norwegian scientist. V=k c A a c B b 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.
Factor under study Substances used conclusion Concentration of reactants HCl 10% HCl 20% +Zn +Zn v 1 
Mathematical expression of the law of mass action. According to the law of mass action, the reaction rate, the equation of which is A + B = C, can be calculated by the formula: v 1 = k 1 C A C B, and the reaction rate, the equation of which is A + 2 B = D, can be calculated by the formula: v 2 = k 2 C A C B. In these formulas: C A and C B are the concentrations of substances A and B (mol/l), k 1 and k 2 are proportionality coefficients, called reaction rate constants. These formulas are also called kinetic equations.
3. Contact surface of reacting substances. The reaction speed increases due to: -increasing the surface area of contact of the reagents (grinding); -increasing the reactivity of particles on the surface of microcrystals formed during grinding; - continuous supply of reagents and good removal of products from the surface where the reaction takes place. The factor is associated with heterogeneous reactions that occur on the contact surface of reacting substances: gas - solid, gas - liquid, liquid - solid, liquid - another liquid, solid - another solid, provided that they are insoluble in each other .
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4. Temperature For every 10° C increase in temperature, the total number of collisions increases by only ~ 1.6%, and the reaction rate increases by 2-4 times (by %). 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 J. Van't Hoff (). Dutch chemist. One of the founders of physical chemistry and stereochemistry. For every 10 C increase in temperature, the reaction rate increases by 2-4 times.
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5. Action of a catalyst It is possible to 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 are substances that participate in a chemical reaction and increase its speed, but at the end of the reaction remain unchanged qualitatively and quantitatively. Inhibitors are substances that slow down chemical reactions. Changing the rate of a chemical reaction or its direction using a catalyst is called catalysis.
There are two types of catalysis: Homogeneous catalysis, in which both the catalyst and the reactants are in the same state of aggregation (phase). – For example, enzymatic catalytic reactions in the cells of the body take place in an aqueous solution. Heterogeneous catalysis, in which the catalyst and reactants are in different phases. – For example, the decomposition of hydrogen peroxide in the presence of a solid manganese(IV) oxide catalyst: MnO 2 (t) 2H 2 O 2 (l) 2H 2 O (l) + O 2 (g)
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