Download presentation rate of a chemical reaction. The history of the development of analytical chemistry - presentation

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Lesson topic: "The rate of chemical reactions." The purpose of the lesson: To know the definition of the speed of reacting substances, from reactions; dependence of the speed on the nature of the contact surface, on the concentration, on the temperature, on the catalyst. Be able to explain the influence of various conditions on the rate of chemical reactions.

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for homogeneous reactions. The rate of a chemical reaction is the change in the concentration of one of the reactants or one of the reaction products per unit time ∆c V = ------------- ∆ t

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For heterogeneous reactions. Velocity is determined by the change in the amount of matter per unit time per unit surface of the solid.

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Factors affecting the rate of reactions. 1. The nature of the reactants. 2.Concentration of substances. 3. Area of ​​contact of reactants. 4.Temperature. 5. Catalyst.

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The nature of the reactants 1) Interaction of Na and K with water. 2) Interaction of halogens with aluminum or hydrogen. The rate of the given OVR depends on the electronic nature of the substances. Explain this dependence using the knowledge of the electronic structure of the atoms of the reacting substances.

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The concentration of substances. (in a dissolved or gaseous state) 1) The combustion of sulfur in air or in pure oxygen. 2) Interaction of Zn with dilute and concentrated HCl. The reaction rate is directly proportional to the concentration of reactants. Explain this relationship in terms of the number of active collisions between molecules.

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Surface area of ​​contact of the reactants. (for heterogeneous reactions) Example: reaction of hydrochloric acid with Zn in the form of granules and in the form of a powder. The more crushed the substance, the greater the area of ​​​​contact of the reacting substances and the faster the reaction. The contact surface can be increased by applying the "fluidized bed" principle. Explain these phenomena.

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The rate of chemical reactions Chemical kinetics studies the rate and mechanisms of chemical reactions.

Homogeneous and heterogeneous systems Heterogeneous systems A phase is a set of all homogeneous parts of a system that are identical in composition and in all physical and chemical properties and separated from other parts of the system by an interface. Homogeneous systems consist of one phase

The rate of chemical reactions (for homogeneous systems) A + B \u003d D + G C 0 \u003d 0.5 mol / l C 1 \u003d 5 mol / l  t \u003d 10 s

The rate of chemical reactions (for homogeneous systems) A + B \u003d D + G C 0 \u003d 2 mol / l C 1 \u003d 0.5 mol / l  t \u003d 10 s (for heterogeneous systems)

Factors on which the reaction rate depends Nature of the reactants Concentration of substances in the system Surface area (for heterogeneous systems) Temperature Presence of catalysts Experiment: effect of concentration Experiment: alkali metals react with water Rubidium and cesium with water

Effect of temperature Van't Hoff's rule When the system is heated by 10 ˚С, the reaction rate increases by 2-4 times - Van't Hoff temperature coefficient Jacob Van't Hoff (1852-1911)

Catalysis Jens Jakob Berzelius coined the term "catalysis" in 1835. A catalyst is a substance that changes the rate of a reaction and participates in the intermediate stages of the reaction, but is not part of the reaction products. 2SO 2 (g) + O 2 (g) 2SO 3 (g) 2) SO 2 (g) + NO 2 (g)  SO 3 (g) + NO (g) 1) 2 NO (g.) + O 2 (g.)  2NO 2 (g.) Wilhelm Ostwald 1909 - Nobel Prize "in recognition of work on catalysis"

The mechanism of decomposition of hydrogen peroxide 2 H 2 O 2 \u003d 2H 2 O + O 2 (1) H 2 O 2 \u003d H + + HO 2 - (2) HO 2 - + H 2 O 2 \u003d H 2 O + O 2 + OH - (3) OH - + H + = H 2 O Look at the experiment "Decomposition of hydrogen peroxide" Go to the topic "catalysis"

Decomposition of H 2 O 2 in the presence of Fe 3+ H 2 O 2 = H + + HO 2 - HO 2 - + Fe 3+ = Fe 2+ + HO 2 HO 2 + Fe 3+ = Fe 2+ + O 2 + H + Fe 2+ + H 2 O 2 = Fe 3+ + OH + OH - OH + H 2 O 2 = H 2 O + HO 2 Fe 2+ + HO 2 = Fe 3+ + HO 2 - OH - + H + = H 2 O. . . . . . Compare with a mechanism without a catalyst

17 white camels Kai Linderström-Lang (1896-1959) Parable of catalysis + 1 black camel 1/2 1/3 1/9 18 9 6 2 17 + 1 black camel

Terminology Catalysis, catalyst Inhibitor Promoters Catalytic poisons Homogeneous and heterogeneous catalysis Enzymes

Features of enzymatic catalysis High selectivity and specificity of the catalyst Strict requirements for reaction conditions Classification of enzymes Oxireductases Transferases Hydrolases Lyases Isomerases Ligases (synthetases)

Now to the exam questions!

A20-2008-1 The rate of chemical reaction between sulfuric acid solution and iron is not affected by 1) acid concentration 2) iron grinding 3) reaction temperature 4) pressure increase

A20-2008-2 To increase the rate of the chemical reaction Mg (s.) + 2 H + = Mg 2+ + H 2 (g.) it is necessary to 1) add a few pieces of magnesium 2) increase the concentration of hydrogen ions 3) reduce the temperature 4) increase concentration of magnesium ions

A20-2008-3 With the highest rate under normal conditions, the reaction proceeds 1) 2 Ba + O 2 = 2BaO 2) Ba 2+ + CO 3 2- = BaCO 3 ↓ 3) Ba + 2H + = Ba 2+ + H 2 4 ) Ba + S = BaS

A20-2008-4 To increase the rate of the reaction 2CO + O 2 = 2CO 2 + Q, it is necessary to 1) increase the concentration of CO 2) decrease the concentration of O 2 3) lower the pressure 4) lower the temperature

A20-2008- 5 To increase the reaction rate of Zn (solid) + 2 H + = Zn 2+ + H 2 (g) it is necessary to 1) decrease the concentration of zinc ions 2) increase the concentration of hydrogen ions 3) decrease the temperature 4) increase the concentration zinc ions

1) Zn + HCl (5%p-p) 2) Zn + HCl (10%p-p) 3) Zn + HCl (20%p-p) 4) NaOH (5% p-p) + HCl (5% p-p) reaction conditions

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Analytical reactions in solutions Analytical reactions in solutions, reversible and irreversible Chemical equilibrium Law of mass action, chemical equilibrium constant Factors affecting the equilibrium shift of analytical reactions

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Types of chemical reactions in analytical chemistry acid-base reactions - reactions with H+ proton transfer redox reactions (ORR) - reactions with electron transfer ē complex formation reactions - reactions with electron pair transfer and formation of bonds according to the donor-acceptor mechanism Precipitation reactions - heterogeneous reactions in solution

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In quantitative analysis, reversible reactions are widely used, i.e. proceeding simultaneously in two opposite directions: aA + cB ↔ cC + dD The reaction proceeding towards the formation of reaction products is called direct aA + cB → sC + dD , all reactions occurring in nature are reversible, but in cases where the reverse reaction is very weak, the reactions are considered practically irreversible. These usually include those reactions during which one of the products formed leaves the reaction sphere, i.e. precipitate, are released in the form of a gas, a poorly dissociated substance (for example, water) is formed, the reaction is accompanied by the release of a large amount of heat.

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The state of chemical equilibrium is typical only for reversible processes. In reversible reactions, the rate of the direct reaction initially has a maximum value, and then decreases due to a decrease in the concentration of the initial substances consumed for the formation of reaction products. The reverse reaction at the initial moment has a minimum rate, which increases with increasing concentrations of the reaction products. Thus, there comes a moment when the rates of the forward and reverse reactions become equal. This state of the system is called chemical equilibrium

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In 1864 - 1867, the Norwegian scientists Guldberg and Waage established the law of mass action (under the effective masses they meant concentrations. Then the term concentration was not yet known, it was introduced later by van't Hoff): the rate of a chemical reaction is directly proportional to the product of the concentrations of reacting substances in powers, equal to the corresponding stoichiometric coefficients. For a reversible reaction of the type aA + вB = cC + dD, according to the law of action of masses, the rates of the forward and reverse reactions are respectively: If vrev = vorev, then krev[A]a[B]v = korev[C]c[D]d, whence K = karev / krev = [C]c[D]d / [A]a[B]v . Thus, the equilibrium constant is the ratio of the product of the concentrations of the reaction products to the product of the concentrations of the starting substances. The equilibrium constant is a dimensionless quantity, since depends on the concentration and amount of substances.

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The value of K, which characterizes the constancy of the ratios of equilibrium concentrations of reagents at a constant temperature, was called by van't Hoff the equilibrium constant. The equilibrium constant is one of the quantitative characteristics of the state of chemical equilibrium. Task: write an expression for the equilibrium constant of the following reactions: H2+I2 ↔ 2HI ; K= 2 / N2+3H2 ↔ 2NH3; K=2 / 3

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The direction of the shift of chemical equilibrium with changes in concentration, temperature and pressure is determined by the principle of Le - Chatelier: if the system in equilibrium is affected (change in concentration, temperature, pressure), then the equilibrium in the system shifts in the direction of weakening this effect LE CHATELIER Henri Louis

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For the reaction A + B ↔ C + D Concentration change If the concentration of the starting substances increases, then the equilibrium shifts towards the formation of reaction products, i.e. to the right A + B → C + D, if the concentration of the starting substances decreases, then the equilibrium shifts towards the starting substances, i.e. to the left A + B ← C + D if the concentration of the reaction products increases, then the equilibrium shifts towards the formation of the starting substances, i.e. to the left A + B ← C + D, if the concentration of reaction products decreases, then the equilibrium shifts towards the formation of reaction products, i.e. right, A+B → C+D

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For the reaction A + B ↔ C + D to the right A + B → C + D, if the temperature increases, then the equilibrium shifts towards the starting substances, i.e. to the left A + B ← C + D in an endothermic process (positive value of the reaction) - if the temperature increases, then the equilibrium shifts towards the formation of reaction products, i.e. to the right A + B → C + D, if the temperature decreases, then the equilibrium shifts towards the formation of the starting substances, i.e. left A+B ← C+D

Lecture plan 1. Chemical kinetics 2. The rate of chemical reactions 3. The effect of concentration on the rate of chemical reactions 4. The effect of temperature on the rate of chemical reactions 5. The effect of the nature of reacting substances on the rate of chemical reactions 6. The effect of contact area on the rate of heterogeneous reactions 7. The effect of a catalyst on the speed and path of chemical reactions 8. Catalysts in chemical production and in biological objects

The essence of chemical reactions 1) The essence of chemical reactions is reduced to the breaking of bonds in the starting substances and the emergence 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 - with the absorption of energy.

For homogeneous reactions The rate of a chemical reaction is understood as the change in the concentration of one of the reactants per unit time with 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 \u003d - \u003d MOL L * C

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: mА + 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 С v 2 \u003d v 1 ٠

The physical meaning of the temperature coefficient If the temperature coefficient is 3, this means that the reaction rate increases by 3 times, with an increase in temperature by 10 0 C. With an increase in temperature by another 10 0 C, the reaction rate will increase by 3 2 \u003d 9 times.

Area of ​​contact of the reactants The rate of heterogeneous reactions depends on the area of ​​contact of the substances. Heterogeneous reactions occur only at the interface of the reactants. The rate of a heterogeneous reaction is expressed by the formula: t * S V heterog. \u003d MOL m 2 * C

Influence of a catalyst on the chemical reaction path of butadiene-1,3 ethyl acetate acetaldehyde ethylene diethyl ether

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Definition:

The rate of a chemical reaction is the change in the amount of reactant per unit time per unit volume.

r - chemical reaction rate, V - volume m3, Dv - amount of substance in moles, Dt - time interval sec., DC - molar concentration (Dv / V)

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Explanation:

In other words, the rate of a reaction is the change in the concentration of one of the reactants per unit time.

In the reaction: N2+3H2=2NH3, 1 mol of N2 reacts with 3 mols of H2 and 2 mols of NH3 is obtained. = with

Thus, the rate of a chemical reaction can be calculated for any participant in the reaction based on the coefficients of the reaction equation

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Reaction rate, factors:

Factor of internal chemical bonds: The nature of the reacting substances (strength of chemical bonds in a substance) def: chemical reaction - the process of redistribution of chemical bonds between atoms, as a result of which new substances are formed. The stronger the internal chemical bonds in a substance, the more difficult it is to react.

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Temperature factor (activation energy): def: Activation energy is the energy of an intermediate state, above which the total energy of the reacting particles is greater than the energy of the reactants that have not yet reacted. In the intermediate state, old chemical bonds have already been broken, and new ones have not yet been formed. For reactions occurring at in the range of 273-373 degrees Kelvin, the van't Hoff rule is fulfilled: when the temperature rises by 10 degrees, the reaction rate increases by 2-4 times.

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Catalyst Factor: def: Catalyst is an intermediate reagent that lowers the activation energy of a chemical reaction due to the formation of intermediate compounds with lower energy costs. def: Catalyst - substances or external influences (eg ultrasound or ionizing radiation) that accelerate various chemical and physical processes (eg polymerization) in a given direction. The main function of a catalyst is to form more reactive intermediates and complexes with the starting materials, which make it possible to reduce the activation energy of a chemical reaction.

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Inhibitor Factor: def: Inhibitor - a substance that slows down or prevents the course of various chemical reactions: oxidation, polymerization, corrosion of metals, etc. For example, hydroquinone is an inhibitor of benzaldehyde oxidation; technetium compounds - corrosion inhibitor of steels. The main function of an inhibitor is to form less reactive intermediates and complexes with the initial substances, which make it possible to increase the activation energy of a chemical reaction.

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Concentration Factor (Law of Mass Action) def: The Law of Mass Action establishes the ratio between the masses of reactants in chemical reactions at equilibrium. The law of mass action was formulated in 1864-1867. K. Guldberg and P. Waage. According to this law, the rate at which substances react with each other depends on their concentration. The law of mass action is used in various calculations of chemical processes. It allows you to decide in which direction the spontaneous course of the reaction under consideration is possible at a given ratio of the concentrations of the reactants, what yield of the desired product can be obtained.

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Concentration Factor (Law of Mass Action) def: The equilibrium constant is a constant value obtained from the ratio of the product of the concentrations of the reaction products (in powers of their coefficients in the reaction equation) to the product of the concentrations of the reactants (also in powers of their coefficients in the reaction equation). This constant does not depend on the initial concentrations of substances and the reaction mixture. Example: