Presentation on the topic The speed of chemical reactions presentation for a lesson in chemistry (Grade 11) on the topic. The rate of chemical reactions. Factors affecting the rate (presentation) The rate of chemical reactions catalysis presentation
Plan: The rate of a chemical reaction Heterogeneous and homogeneous reactions Dependence of the reaction rate on various factors: – Nature of reacting substances – Concentration of substances – Area of contact of substances – Temperature – Presence of catalysts or inhibitors
The rate of a reaction is determined by the change in the amount of a substance per unit time. In the unit V (for homogeneous) On the unit of the contact surface of substances S (for heterogeneous) n is the change in the amount of substance (mol); t - time interval (s, min) - change in molar concentration;
The task of applying knowledge on "Speed chemical reactions» The chemical reaction proceeds in solution according to the equation: A + B \u003d C. Initial concentrations: substances A - 0.80 mol / l, substances 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) the concentration of substance C after 20 minutes.
Self-test. Given: C (A) 1 \u003d 0.80 mol / l C (B) 1 \u003d 1.00 mol / l C (A) 2 \u003d 0.74 mol / l \u003d 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 \u003d C According to the equation 1 mol 1 mol According to the condition 0.06 mol 0.06 mol The number of reacted substances. Therefore, C (B) 2 \u003d C (B) 1 - C \u003d 1.00 -0.06 \u003d 0.94 mol / l Answer: homogeneous. \u003d 0.003 mol / l C (B) 2 \u003d 0.94 mol / l
collision theory. The main idea of the theory: reactions occur when particles of reactants that have a certain energy collide. The more reagent particles, the closer they are to each other, the more likely they are to collide and react. Only effective collisions lead to the reaction, i.e. those in which "old ties" are destroyed or weakened and therefore "new" ones can form. 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.
Studied factor Substances used Conclusion Nature of the reactants HCl ux. acid + Zn + Zn V 1 > V 2 The more active the substance that reacts, the faster this reaction proceeds. V 2 The more active the substance that reacts, the faster this reaction goes. "> V 2 The more active the substance that enters the reaction, the faster this reaction goes."> V 2 reaction." title="(!LANG:Factor under study Substances used conclusion Nature of the reactants HCl acetic acid +Zn +Zn V 1 > V 2 The more active the reactant, the faster the reaction."> title="Studied factor Substances used Conclusion Nature of the reactants HCl ux. acid + Zn + Zn V 1 > V 2 The more active the substance that reacts, the faster this reaction proceeds."> !}
2. Concentrations of reactants. On the basis of a large amount of experimental material in 1867, the Norwegian scientists K. Guldberg and P Vaage, and independently of them in 1865, the Russian scientist N.I. Beketov formulated the basic law of chemical kinetics, which establishes the dependence of the reaction rate on the concentrations of reactants.
The law of active masses. 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 reactants, taken to powers equal to their coefficients in the reaction equation.
Studied factor Substances used conclusion Concentration of reactants НCl 10% HCl 20% +Zn +Zn v 1 
Mathematical expression of the law of acting masses. According to the law of mass action, the reaction rate, the equation of which A + B \u003d C can be calculated by the formula: v 1 \u003d k 1 C A C B, and the reaction rate, the equation of which A + 2B \u003d D, can be calculated by the formula: v 2 \u003d 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. The contact surface of the reactants. The reaction rate increases due to: - an increase in 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 the reacting substances: gas - solid, gas - liquid, liquid - solid, liquid - another liquid, solid - another solid, provided that they are insoluble in each other .
V 2 The larger the contact area of the reactants, the higher the rate of the chemical reaction." title="(!LANG: Study factor Substances used output Contact area of the reactants Fe (powder) Fe (button) + HCl + HCl V 1 > V 2 The larger the contact area of the reactants, the higher the rate of the chemical reaction." class="link_thumb"> 23 !} Studied factor Substances used conclusion Contact area of reactants Fe (powder) Fe (button) + HCl + HCl V 1 > V 2 The larger the contact area of the reactants, the higher the rate of chemical reaction. V 2 The larger the area of contact of the reactants, the higher the rate of the chemical reaction."> V 2 The larger the area of contact of the reactants, the higher the rate of the chemical reaction."> V 2 higher speed of chemical reaction." title="(!LANG:Factor under study Substances used output Contact area of reactants Fe (powder) Fe (button) + HCl + HCl V 1 > V 2 The larger the contact area of reactants, the higher rate of chemical reaction."> title="Studied factor Substances used conclusion Contact area of reactants Fe (powder) Fe (button) + HCl + HCl V 1 > V 2 The larger the contact area of the reactants, the higher the rate of chemical reaction."> !}
4. Temperature With an increase in temperature for every 10°C, the total number of collisions increases only by ~ 1.6%, and the reaction rate increases by a factor of 2-4 (by %). The number showing how many times the reaction rate increases with an increase in temperature by 10 ° C is called the temperature coefficient.
Van't Hoff's rule Ya. Van't Hoff (). Dutch chemist. One of the founders of physical chemistry and stereochemistry When the temperature rises for every 10 C, the reaction rate increases by 2-4 times.
Studied factor Substances used conclusion Temperature Al Al + HCl + HCl + t V 1 > V 2 When heated, the rate of a chemical reaction increases. V 2 When heated, the rate of a chemical reaction increases."> V 2 When heated, the rate of a chemical reaction increases."> V 2 When heated, the rate of a chemical reaction increases." title="(!LANG:Study factor Substances used output Temperature Al Al + HCl + HCl +t V 1 > V 2 When heated, the rate of a chemical reaction increases."> title="Studied factor Substances used conclusion Temperature Al Al + HCl + HCl + t V 1 > V 2 When heated, the rate of a chemical reaction increases."> !}
5. Catalyst Action It is possible to change the reaction rate 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 take part 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 with the help of 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)
V 2 Catalysts are substances that speed up the rate of a chemical reaction. Inhibitors - reduce the rate of the reaction." title="(!LANG: Studied factor Substances used conclusion Presence of certain substances H 2 O 2 H 2 O 2 +MnO 2 V 1 > V 2 Catalysts - substances that speed up the rate of a chemical reaction. Inhibitors - reduce speed reaction." class="link_thumb"> 31 !} Studied factor Substances used conclusion The presence of certain substances H 2 O 2 H 2 O 2 + MnO 2 V 1 > V 2 Catalysts are substances that accelerate the rate of a chemical reaction. Inhibitors - slow down the rate of a reaction. V 2 Catalysts are substances that speed up the rate of a chemical reaction. Inhibitors - reduce the rate of a reaction. "> V 2 Catalysts - substances that speed up the rate of a chemical reaction. Inhibitors - reduce the rate of a reaction."> V 2 Catalysts - substances that speed up the rate of a chemical reaction. Inhibitors - reduce the rate of the reaction." title="(!LANG: Studied factor Substances used conclusion Presence of certain substances H 2 O 2 H 2 O 2 +MnO 2 V 1 > V 2 Catalysts - substances that speed up the rate of a chemical reaction. Inhibitors - reduce speed reaction."> title="Studied factor Substances used conclusion The presence of certain substances H 2 O 2 H 2 O 2 + MnO 2 V 1 > V 2 Catalysts are substances that accelerate the rate of a chemical reaction. Inhibitors - slow down the rate of a reaction."> !}
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CLASSIFICATION OF CHEMICAL REACTIONS ON THE SIGN OF PHASE (AGGREGATE STATE) CHEMICAL REACTIONS HOMOGENEOUS HETEROGENEOUS (reacting substances and reaction products are in the same phase) 2SO2 (g) + O2 (g) \u003d 2SO3 (g) HCl (l) + NaOH (l) \u003d NaCl (l) + H2O Feature: flow in the entire volume of the reaction mixture (reacting substances and reaction products are in different phases) S (tv) + O2 (g) = SO2 (g) Zn (tv) + 2HCl (l) = ZnCl2 g)+H2(d) Feature: flow at the interface
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REACTION RATES The rate of a homogeneous reaction The rate of a heterogeneous reaction А (g) + В (g) = С (g) 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 affecting the rate of a chemical reaction Concentration А+B=C+D V=k[A]*[B] Nature of the reactants Contact surface area temperature catalyst
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Task 1 At some point in time, the concentration of chlorine in the vessel in which the reaction H2+Cl2=2HCl was taking 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 given time interval? Given С1(Cl2)=0.06 mol/l С2(Сl2)=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 FeCl3 + 3KCNS = Fe(CNS)3 + 3KCl reaction occurring in an aqueous solution change when the reacting mixture is diluted with water twice 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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Task 3 How will the reaction rate change with an increase in temperature from 55 to 100 °C, if the temperature coefficient of the reaction rate 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 rate of the reaction increases by 43.7 times
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Task 4 When the temperature rises by 30 °C, the rate of some reaction increases by 64 times. What is the temperature coefficient for 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 to: a) increase the concentration of reactants 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 air in ) dissolution of magnesium in acid d) reduction of copper oxide with hydrogen 3. Indicate 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. Note which reaction is both homogeneous and catalytic. a) 2SO2+O2=2SO3 (cat NO2) b) CaO+CO2=CaCO3 c) H2+Cl2=2HCl d) N2+3H2=2NH3 (cat Fe)
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Quiz: consolidation of knowledge 6. Indicate how the rate of the bimolecular gas reaction 2NO2=N2O4 will change with an increase in the concentration of NO2 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 of 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 is unchanged). a) 2NO+O2=2NO2 b) H2+Cl2=2HCl c) CaO+H2O=Ca(OH)2 d) N2O4=2NO2 speed decreased by 81 times.
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Slides captions:
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 delimited from other parts of the system by the 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 Experience: effect of concentration Experience: 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 (solid) + 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) decrease the temperature 4) increase concentration of magnesium ions
A20-2008-3 With the highest speed at 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 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
State budgetary educational institution higher professional education "Kazan State Medical University" of the Ministry of Health Russian Federation MEDICAL-PHARMACEUTICAL COLLEGE The history of the development of analytical chemistry Completed by: Davletshina Gulnaz R group
Analytical chemistry is the science of methods for determining the chemical composition of a substance and its structure. However, this definition of CS seems to be exhaustive. The subject of analytical chemistry is the development of methods of analysis and their practical implementation, as well as a broad study of the theoretical foundations of analytical methods. This includes the study of the forms of existence of elements and their compounds in various media and states of aggregation, the determination of the composition and stability of coordination compounds, the optical, electrochemical and other characteristics of a substance, the study of the rates of chemical reactions, the determination of the metrological characteristics of methods, etc. new methods of analysis and the use of modern achievements of science and technology for analytical purposes.
Depending on the task, the properties of the analyzed substance and other conditions, the composition of substances is expressed in different ways. Chemical composition substances can be characterized by the Mass fraction (%) of elements or their oxides or other compounds, as well as the content of individual chemical compounds or phases, isotopes, etc. actually present in the sample, etc. The composition of alloys is usually expressed mass fraction(%) constituent cements; the composition of rocks, ores, minerals, etc., the content of elements in terms of any of their compounds, most often oxides.
Theoretical basis analytical chemistry are the fundamental laws of natural science, such as the periodic law of D. I. Mendeleev, the laws of conservation of mass of matter and energy, the constancy of the composition of matter, acting masses, etc. Analytical chemistry is closely related to physics, inorganic, organic, physical and colloidal chemistry, electrochemistry, chemical thermodynamics, solution theory, metrology, information theory and many other sciences.
Analytical chemistry is of great scientific and practical importance. Almost all the basic chemical laws have been discovered using the methods of this science. Compound various materials, products, ores, minerals, lunar soil, distant planets and other celestial bodies established by methods of analytical chemistry, the discovery of a number of elements of the periodic system was made possible through the use of precise methods of analytical chemistry. Importance of Analytical Chemistry
Many practical methods of analytical chemistry and analytical techniques were known in ancient times. This is, first of all, assay art, or assay analysis, which was performed in a “dry” way, that is, without dissolving the sample and using solutions. The assay analysis methods controlled the purity of noble metals and determined their content in ores, alloys, etc. The assay analysis technique reproduced in laboratory conditions manufacturing process receiving precious metals. These methods of analysis were used in ancient Egypt and Greece, they were also known in Kievan Rus. The practical significance of reactions in solution was not great at that time. Main stages in the development of analytical chemistry
The development of industry and various industries by the middle of the XVII century. required new methods of analysis and research, since assay analysis could no longer satisfy the needs of the chemical and many other industries. By this time, by the middle of the XVII century. usually refer to the emergence of analytical chemistry and the formation of chemistry itself as a science. Determination of the composition of ores, minerals and other substances aroused great interest, and chemical analysis became at that time the main research method in chemical science. R. Boyle () developed general concepts about chemical analysis. He laid the foundations of modern qualitative analysis in a “wet” way, i.e., by carrying out reactions in a solution, he also cited a system of qualitative reactions known at that time and proposed several new ones (for ammonia, chlorine, etc.), applied litmus to detect acids and alkalis and made other important discoveries.
M. V. Lomonosov () for the first time began to systematically use balance in the study of chemical reactions. In 1756, he experimentally established one of the basic laws of nature, the law of conservation of the mass of matter, which formed the basis of quantitative analysis and is of great importance for all science. M. V. Lomonosov developed many methods of chemical analysis and research that have not lost their significance to this day (filtering under vacuum, gravimetric analysis operations, etc.). The merits of M. V. Lomonosov in the field of analytical chemistry include the creation of the foundations of gas analysis, the use of a microscope to conduct a qualitative analysis of the shape of crystals, which later led to the development of microcrystalloscopic analysis, the design of a refractometer and other instruments. The results of his own research and the experience of a research chemist, analyst and technologist M. V. Lomonosov summarized in the book “The First Foundations of Metallurgy or Mining” (1763), which had a huge impact on the development of analytical chemistry and related fields, as well as metallurgy and mining.
The use of precise methods of chemical analysis made it possible to determine the composition of many natural substances and products of technological processing, to establish a number of basic laws of chemistry. A. L. Lavoisier () determined the composition of air, water and other substances and developed the oxygen theory of combustion. Based on analytical data, D. Dalton () developed the atomistic theory of matter and established the laws of composition constancy and multiple ratios. J. L. Gay-Lussac () and A. Avogadro () formulated gas laws.
M. V. Severgin () proposed a colorimetric analysis based on the dependence of the color intensity of a solution on the concentration of a substance, J. L. Gay-Lussac developed a titrimetric method of analysis. These methods, together with the gravimetric method, formed the basis of classical analytical chemistry and have retained their significance to the present day. Analytical chemistry, enriched by new methods, continued to develop and improve. At the end of the XVIII century. T. E. Lovits (), developing the ideas of M. V. Lomonosov, created microcrystalloscopic analysis, a method for the qualitative analysis of salts in the form of their crystals.
At the end of the XVIII and XIX centuries. the works of many scientists T. W. Bergman (), L. J. Tenard (), K. K. Klaus () and others created a systematic qualitative analysis. In accordance with the developed scheme, certain groups of elements were precipitated from the analyzed solution by the action of group reagents, and then individual elements were discovered within these groups. This work was completed by K. R. Fresenius (), who wrote textbooks on qualitative and quantitative analysis and founded the first journal in analytical chemistry (Zeitschrift fur analytische Chemie, now Fresenius Z. anal. Chem.). At the same time, I. Ya. Berzelius () and Yu. Liebig () improved and developed methods for analyzing organic compounds for the content of basic elements C, H, N, etc. Titrimetric analysis progresses noticeably, methods of iodometry, permanganatometry, etc. discovery is made in R. V. Bunsen () and G. R. Kirchhoff (). They offer spectral analysis, which becomes one of the main methods of analytical chemistry, continuously developing up to the present.
A huge influence on the development of chemistry and other sciences was made by the discovery in 1869 by D. I. Mendeleev () of the periodic law, and D. I. Mendeleev’s Fundamentals of Chemistry became the basis for the study of analytical chemistry. The creation by A. M. Butlerov of the theory of the structure of organic compounds was also of great importance. A. A. Menshutkin's "Analytical Chemistry" published in 1871 (), which went through 16 editions in our country and was translated into German and English languages. In 1868, on the initiative of D.I. Mendeleev and N. A. Menshutkin, the Russian Chemical Society was established at St. Petersburg University, which began to publish its own journal in 1869. The creation of a scientific chemical society and the publication of a journal had a beneficial effect on the development of domestic chemistry and analytical chemistry in particular.
A special section of chemistry was developed by N. S. Kurnakov () physico-chemical analysis, based on the study of “composition-property” diagrams. The method of physicochemical analysis makes it possible to establish the composition and properties of compounds formed in complex systems by the dependence of the properties of the system on its composition without isolating individual compounds in crystalline or other form.
In 1903, M. S. Tsvet () proposed a chromatographic analysis effective method separation of compounds with similar properties, based on the use of adsorption and some other properties of the substance. The merits of this method were fully appreciated only a few decades after its discovery. For the development of partition chromatography, A. Martin and R. Sing were awarded the Nobel Prize in 1954.
Further development of the theory of analytical chemistry is associated with the discovery by N. N. Beketov () of the equilibrium nature of chemical reactions and K. M. Guldberg () and II. Waage () of the law of mass action. With the advent in 1887 of the theory of electrolytic dissociation by S. Arrhenius (), analytical chemists received a method for the effective quantitative control of chemical reactions, and the success of chemical thermodynamics further expanded these possibilities. A significant role in the development of the scientific foundations of analytical chemistry was played by the monograph by W. Ostwald () "Scientific foundations of analytical chemistry in an elementary presentation", published in 1894. Of great importance for the development redox methods of analytical chemistry were the works of L. V. Pisarzhevsky () and N. A. Shilov () on the electronic theory of redox processes.
From the 20s of the XX century. Quantitative emission spectral analysis and absorption spectroscopy begin to develop intensively. Devices with photoelectric recording of light intensity are being designed. In 1925, J. Geyrovsky () developed a polarographic analysis, for which in 1959 he was awarded the Nobel Prize. In the same years, chromatographic, radiochemical and many other methods of analysis were developed and improved. Since 1950, the method of atomic absorption spectroscopy proposed by E. Walsh has been rapidly developing.
The development of industry and science demanded from analytical chemistry new advanced methods of analysis. There was a need for quantitative determinations of impurities at the level and below. It turned out, for example, that the content of the so-called forbidden impurities (Cd, Pb, etc.) in materials rocket technology should not exceed 10~5%, the content of hafnium in zirconium used as a structural material in nuclear technology should be less than 0.01%, and in materials of semiconductor technology, impurities should be no more than 10%. It is known that the semiconductor properties of germanium were discovered only after samples of this element of high purity were obtained. Zirconium was initially rejected as a structural material in the nuclear industry on the grounds that it quickly became radioactive itself, although according to theoretical calculations this should not have been the case. Later it turned out that it was not zirconium that became radioactive, but the usual companion of zirconium, hafnium, which is found as an impurity in zirconium materials.
The present day of analytical chemistry is characterized by many changes: the arsenal of methods of analysis is expanding, especially in the direction of physical and biological ones; automation and mathematization of analysis; creation of methods and means of local, non-destructive, remote, continuous analysis; approach to solving problems about the forms of existence of components in the analyzed samples; the emergence of new opportunities to improve the sensitivity, accuracy and speed of analysis; further expansion of the range of analyzed objects. Computers are now widely used, lasers do a lot, laboratory work has appeared; the role of analytical control, especially the objects of our environment, has risen significantly. Interest in the methodological problems of analytical chemistry has grown. How to clearly define the subject of this science, what place it occupies in the system of scientific knowledge, whether it is fundamental or applied science, what stimulates its development, these and similar questions have been the subject of many discussions.
So, we see that for the chemical reaction of the molecule starting materials must first overcome the activation barrier Ea. Thus, the activation barrier can be an obstacle to the spontaneous occurrence of even very “favorable” exothermic reactions from an energetic point of view. For example, if there were no activation barrier, the combustion reaction of methane in oxygen would begin immediately after the contact of methane with air. In this case, not only natural gas (it contains 95% methane), but also oil, gasoline, coal, paper, clothes, furniture, wooden buildings and everything that, in principle, can burn, would have to be carefully isolated from the air. Fortunately, the activation barrier Ea stands in the way of spontaneous occurrence of these exothermic reactions. When we bring a burning match to an open burner of a gas stove, we force some part of the methane and oxygen molecules to "jump" the activation barrier, which is not overcome at room temperature. In the future, the activation energy for the interaction of more and more methane and oxygen molecules is already drawn from the heat of the exothermic reaction itself.
