Chemistry and energy. The value of chemistry in solving the energy problem - abstract
abstract
The role of chemistry in solving energy problems
Introduction
The whole history of the development of civilization is the search for energy sources. This is very relevant even today. After all, energy is an opportunity for the further development of industry, obtaining sustainable crops, beautifying cities and helping nature heal the wounds inflicted by civilization. Therefore, the solution of the energy problem requires a global effort. .
1. The origin of modern chemistry and its problems in the 21st century
chemistry society energy
The end of the Middle Ages was marked by a gradual departure from the occult, a decline in interest in alchemy, and the spread of a mechanistic view of the structure of nature.
Iatrochemistry.
Completely different views on the goals of alchemy were held by Paracelsus. Under such a name chosen by him, the Swiss doctor Philipp von Hohenheim went down in history. Paracelsus, like Avicenna, believed that the main task of alchemy was not the search for ways to obtain gold, but the manufacture of medicines. He borrowed from the alchemical tradition the doctrine that there are three main parts of matter - mercury, sulfur, salt, which correspond to the properties of volatility, combustibility and hardness. These three elements form the basis of the macrocosm and are associated with the microcosm formed by the spirit, soul and body. Turning to the definition of the causes of diseases, Paracelsus argued that fever and plague come from an excess of sulfur in the body, paralysis occurs with an excess of mercury, and so on. The principle that all iatrochemists adhered to was that medicine is a matter of chemistry, and everything depends on the ability of the doctor to isolate pure principles from impure substances. Within this scheme, all the functions of the body were reduced to chemical processes, and the task of the alchemist was to find and prepare chemical substances for medical needs.
The main representatives of the iatrochemical direction were Jan Helmont, a doctor by profession; Francis Silvius, who enjoyed great fame as a physician and eliminated "spiritual" principles from the iatrochemical doctrine; Andreas Libavius, physician from Rothenburg.
Their research contributed greatly to the formation of chemistry as an independent science.
mechanical philosophy.
With the diminishing influence of iatrochemistry, natural philosophers turned again to the teachings of the ancients about nature. Foreground in the 17th century. atomistic views emerged. One of the most prominent scientists - authors of the corpuscular theory - was the philosopher and mathematician Rene Descartes. He outlined his views in 1637 in his Discourse on Method. Descartes believed that all bodies “consist of numerous small particles of various shapes and sizes, which are not so closely adjacent to each other that there are no gaps around them; these gaps are not empty, but filled with ... rarefied matter. Descartes did not consider his “small particles” to be atoms, i.e. indivisible; he stood on the point of view of the infinite divisibility of matter and denied the existence of emptiness.
One of the most prominent opponents of Descartes was the French physicist and philosopher Pierre Gassendi.
Atomism Gassendi was essentially a retelling of the teachings of Epicurus, however, unlike the latter, Gassendi recognized the creation of atoms by God; he believed that God created a certain number of indivisible and impenetrable atoms, of which all bodies are composed; there must be an absolute void between the atoms.
In the development of chemistry in the 17th century. a special role belongs to the Irish scientist Robert Boyle. Boyle did not accept the statements of the ancient philosophers, who believed that the elements of the universe can be established speculatively; this is reflected in the title of his book The Skeptical Chemist. As a supporter of an experimental approach to the definition chemical elements, he did not know about the existence of real elements, although one of them - phosphorus - almost discovered himself. Boyle is usually credited with introducing the term "analysis" into chemistry. In his experiments on qualitative analysis, he used various indicators, introduced the concept of chemical affinity. Based on the works Galileo Galilei Evangelista Torricelli, as well as Otto Guericke, who demonstrated the "Magdeburg hemispheres" in 1654, Boyle described the air pump he designed and experiments to determine the elasticity of air using a U-shaped tube. As a result of these experiments, the well-known law on the inverse proportionality of the volume and pressure of air was formulated. In 1668 Boyle became an active member of the newly organized Royal Society of London, and in 1680 he was elected its president.
Biochemistry. This scientific discipline deals with the study chemical properties biological substances, at first was one of the branches of organic chemistry. It emerged as an independent region in the last decade of the 19th century. as a result of research on the chemical properties of substances of plant and animal origin. One of the first biochemists was the German scientist Emil Fischer. He synthesized substances such as caffeine, phenobarbital, glucose, many hydrocarbons, made a great contribution to the science of enzymes - protein catalysts, first isolated in 1878. The creation of new analytical methods contributed to the formation of biochemistry as a science.
In 1923, the Swedish chemist Theodor Svedberg designed an ultracentrifuge and developed a sedimentation method for determining the molecular weight of macromolecules, mainly proteins. Svedberg's assistant Arne Tiselius in the same year created the method of electrophoresis, a more advanced method for separating giant molecules, based on the difference in the speed of migration of charged molecules in an electric field. At the beginning of the 20th century Russian chemist Mikhail Semenovich Tsvet described a method for separating plant pigments by passing their mixture through a tube filled with an adsorbent. The method was called chromatography.
In 1944, British chemists Archer Martini Richard Synge proposed new version method: they replaced the adsorbent tube with filter paper. This is how paper chromatography appeared - one of the most common analytical methods in chemistry, biology and medicine, with the help of which in the late 1940s and early 1950s it was possible to analyze mixtures of amino acids resulting from the breakdown of various proteins and determine the composition of proteins. As a result of painstaking research, the order of amino acids in the insulin molecule was established, and by 1964 this protein had been synthesized. Now, many hormones are obtained by biochemical synthesis methods, medicines, vitamins.
quantum chemistry. In order to explain the stability of the atom, Niels Bohr combined classical and quantum ideas about the motion of an electron in his model. However, the artificiality of such a connection was obvious from the very beginning. The development of quantum theory led to a change in the classical ideas about the structure of matter, motion, causality, space, time, etc., which contributed to a radical transformation of the picture of the world.
In the late 20s - early 30s of the 20th century, on the basis of quantum theory, fundamentally new ideas about the structure of the atom and the nature of chemical bond.
After the creation by Albert Einstein of the photon theory of light (1905) and his derivation of the statistical laws of electronic transitions in the atom (1917), the wave-particle problem in physics becomes more acute.
If in the XVIII-XIX centuries there were differences between different scientists who used either wave or corpuscular theory to explain the same phenomena in optics, now the contradiction has acquired a fundamental character: some phenomena were interpreted from wave positions, and others - from corpuscular ones. The resolution of this contradiction was proposed in 1924 by the French physicist Louis Victor Pierre Raymond de Broglie, who attributed the wave properties to the particle.
Based on de Broglie's idea of matter waves, the German physicist Erwin Schrödinger in 1926 derived the basic equation of the so-called. wave mechanics, containing the wave function and allowing to determine the possible states of a quantum system and their change in time. Schrödinger gave a general rule for transforming classical equations into wave equations. Within the framework of wave mechanics, an atom could be represented as a nucleus surrounded by a stationary wave of matter. The wave function determined the probability density of finding an electron at a given point.
In the same 1926, another German physicist, Werner Heisenberg, developed his version of the quantum theory of the atom in the form of matrix mechanics, starting from the correspondence principle formulated by Bohr.
According to the correspondence principle, the laws of quantum physics must turn into classical laws when the quantum discreteness tends to zero as the quantum number increases. In more general view The matching principle can be formulated as follows: new theory, which claims to have a wider scope than the old one, should include the latter as a special case. Heisenberg's quantum mechanics made it possible to explain the existence of stationary quantized energy states and to calculate the energy levels various systems.
Friedrich Hund, Robert Sanderson Mulliken and John Edward Lennard-Jones in 1929 create the foundations of the molecular orbital method. The MMO is based on the idea of a complete loss of the individuality of atoms that have combined into a molecule. The molecule, therefore, is not made up of atoms, but is new system formed by several atomic nuclei and electrons moving in their field. Hund also creates a modern classification of chemical bonds; in 1931 he came to the conclusion that there are two main types of chemical bonds - simple, or ?-communications, and ?-connections. Erich Hückel extends the MO method to organic compounds, formulating in 1931 the rule of aromatic stability (4n + 2), establishing the belonging of a substance to the aromatic series.
Thus, in quantum chemistry, two different approaches to understanding the chemical bond are immediately distinguished: the method of molecular orbitals and the method of valence bonds.
Thanks to quantum mechanics, by the 30s of the 20th century, the method of forming a bond between atoms was basically clarified. In addition, within the framework of the quantum mechanical approach, Mendeleev's theory of periodicity received a correct physical interpretation.
Probably the most important stage in the development of modern chemistry was the creation of various research centers engaged in, in addition to fundamental, also applied research.
At the beginning of the 20th century a number of industrial corporations created the first industrial research laboratories. In the USA, the chemical laboratory "DuPont", the laboratory of the "Bell" company, was founded. After the discovery and synthesis of penicillin in the 1940s, and then other antibiotics, large pharmaceutical companies appeared, employing professional chemists. Works in the field of the chemistry of macromolecular compounds were of great practical importance.
One of its founders was the German chemist Hermann Staudinger, who developed the theory of the structure of polymers. An intensive search for ways to obtain linear polymers led in 1953 to the synthesis of polyethylene, and then other polymers with desired properties. Today, the production of polymers is the largest branch of the chemical industry.
Not all advances in chemistry have been good for man. In the production of paints, soaps, textiles, hydrochloric acid and sulfur were used, which posed a great danger to the environment. In the 21st century the production of many organic and inorganic materials will increase due to the recycling of used substances, as well as through the processing of chemical waste, which pose a risk to human health and the environment.
2. The role of chemistry in solving energy problems
The whole history of the development of civilization is the search for energy sources. This is very relevant even today. After all, energy is an opportunity for the further development of industry, obtaining sustainable crops, beautifying cities and helping nature heal the wounds inflicted by civilization. Therefore, the solution of the energy problem requires global efforts. Chemistry makes its considerable contribution as a link between modern natural science and modern technology.
Energy security is the most important condition for the socio-economic development of any country, its industry, transport, Agriculture, spheres of culture and life.
But in the next decade, neither wood, nor coal, nor oil, nor gas will be discounted in the energy sector. At the same time, they must work hard to develop new ways of generating energy.
The chemical industry is characterized by close ties with all sectors of the national economy due to the wide range of products it produces. This area of production is characterized by high material consumption. Material and energy costs in the production of products can range from 2/3 to 4/5 of the cost of the final product.
The development of chemical technology follows the path of the integrated use of raw materials and energy, the use of continuous and waste-free processes, taking into account the environmental safety of the environment, the use of high pressures and temperatures, the achievements of automation and cybernetization.
The chemical industry in particular consumes a lot of energy. Energy is spent on the implementation of endothermic processes, on the transportation of materials, crumbling and grinding of solids, filtering, compressing gases, etc. Significant energy costs are needed in the production of calcium carbide, phosphorus, ammonia, polyethylene, isoprene, styrene, etc. Chemical industries, together with petrochemical industries, are energy-intensive industries. Producing almost 7% of industrial output, they consume within 13-20% of the energy used by the entire industry.
Energy sources are most often traditional non-renewable Natural resources- coal, oil, natural gas, peat, shale. Recently, they have been depleted very quickly. The reserves of oil and natural gas are declining at a particularly accelerated pace, and they are limited and irreparable. Not surprisingly, this creates an energy problem.
For 80 years, one main source of energy was replaced by another: wood was replaced by coal, coal - by oil, oil - by gas, hydrocarbon fuel - by nuclear. By the beginning of the 1980s, about 70% of the world's energy demand was met by oil and natural gas, 25% by hard and brown coal, and only about 5% by other energy sources.
AT different countries The energy problem is solved in different ways, nevertheless, chemistry makes a significant contribution to its solution everywhere. Thus, chemists believe that in the future (approximately another 25-30 years) oil will retain its leadership position. But its contribution to energy resources will noticeably decrease and will be compensated by the increased use of coal, gas, hydrogen energy, nuclear fuel, solar energy, energy of the earth's depths and other types of restorative energy, including bioenergy.
Even today, chemists are worried about the maximum and complex energy-technological use of fuel resources - reducing heat losses to the environment, recycling heat, maximizing the use of local fuel resources, etc.
Since liquid fuel is the most scarce among fuels, large funds have been allocated in many countries to create a cost-effective technology for converting coal into liquid (as well as gaseous) fuel. Scientists from Russia and Germany are cooperating in this area. The essence of the modern process of processing coal into synthesis gas is as follows. A mixture of water vapor and oxygen is supplied to the plasma generator, which is heated up to 3000°C. And then coal dust enters the hot gas torch, and as a result of a chemical reaction, a mixture of carbon monoxide (II) and hydrogen is formed, i.e. synthesis gas. Methanol is obtained from it: CO + 2H2? CH3OH. Methanol can replace gasoline in internal combustion engines. In terms of solution environmental problem it compares favorably with oil, gas, coal, but, unfortunately, its heat of compression is 2 times lower than that of gasoline, and, in addition, it is aggressive towards certain metals and plastics.
Chemical methods have been developed to remove binder oil (contains high molecular weight hydrocarbons), a significant part of which remains in underground pits. To increase the yield of oil into the water that is pumped into the reservoirs, surfactants are added, their molecules are located at the oil-water interface, which increases the mobility of the oil.
The future replenishment of fuel resources is combined with the rational processing of coal. For example, crushed coal is mixed with oil, and the extracted paste is treated with pressurized hydrogen. In this case, a mixture of hydrocarbons is formed. About 1 ton of coal and 1500 m of hydrogen are spent on the extraction of 1 ton of artificial gasoline. So far, artificial gasoline is more expensive than that produced from oil, however, the fundamental possibility of obtaining it is important.
Hydrogen energy seems to be very promising, which is based on the combustion of hydrogen, during which harmful emissions do not occur. Nevertheless, for its development it is necessary to solve a number of problems related to reducing the cost of hydrogen, creating reliable means of its storage and transportation, etc. If these tasks are solvable, hydrogen will be widely used in aviation, water and land transport, industrial and agricultural production.
Nuclear energy contains inexhaustible possibilities, its development for the production of electricity and heat makes it possible to release a significant amount of organic fuel. Here, chemists are faced with the task of creating complex technological systems for covering the energy costs that occur during the implementation of endothermic reactions using nuclear energy. Now nuclear power is developing along the path of widespread introduction of fast neutron reactors. Such reactors use uranium enriched in the 235U isotope (at least 20%), and a neutron moderator is not required.
Currently, nuclear power and reactor building is a powerful industry with a large amount of capital investment. For many countries, it is an important export item. Reactors and auxiliary equipment require special materials, including those of high frequency. The task of chemists, metallurgists and other specialists is the creation of such materials. Chemists and representatives of other related professions are also working on uranium enrichment.
Now the nuclear power industry is faced with the task of displacing fossil fuels not only from the production of electricity, but also from heat supply and, to some extent, from the metallurgical and chemical industries by creating reactors of energy-technological significance.
Nuclear power plants in the future will find another application - for the production of hydrogen. Part of the resulting hydrogen will be consumed by the chemical industry, the other part will be used to power gas turbine plants that are switched on at peak loads.
Great hopes are placed on the use of solar radiation (solar energy). Solar panels operate in Crimea, photovoltaic cells of which turn sunlight into electricity. For water desalination and home heating, solar thermal plants are widely used, which convert solar energy into heat. Solar panels have long been used in navigation facilities and on spaceships. AT
unlike nuclear, the cost of energy produced by solar panels is constantly decreasing. For the manufacture of solar cells, the main semiconductor material is silicon and silicon compounds. Chemists are currently working on the development of new energy converter materials. These can be different systems of salts as energy storage devices. Further success in solar energy depends on the materials that chemists will offer for energy conversion.
In the new millennium, the increase in electricity production will occur due to the development of solar energy, as well as methane fermentation of household waste and other non-traditional sources of energy production.
Along with giant power plants, there are also autonomous chemical current sources that convert the energy of chemical reactions directly into electrical energy. In solving this problem, chemistry belongs the main role. In 1780, the Italian physician L. Galvani, observing the contraction of the cut off leg of a frog after touching it with wires of different metals, decided that there was electricity in the muscles, and called it "animal electricity." A. Volta, continuing the experience of his compatriot, suggested that the source of electricity is not the body of an animal: an electric current arises from the contact of different metal wires. The "ancestor" of modern galvanic cells can be considered the "electric pole", created by A. Volta in 1800. This invention is similar to a layer cake of several pairs of metal plates: one plate is made of zinc, the second is made of copper, stacked on top of each other, and between they placed a felt pad soaked in dilute sulfuric acid. Before the invention in Germany by W. Siemens in 1867 of the dynamo, galvanic cells were the only source of electric current. Nowadays, when autonomous energy sources are needed for aviation, submarine fleet, rocket technology, electronics, the attention of scientists is again drawn to them.
Conclusion
The use of nuclear energy makes it possible to abandon natural coal and oil. As a result, emissions of their combustion products are reduced, which would possibly lead to a “greenhouse effect” on Earth. It would seem that a negligible (compared to coal and oil) amount of fuel for nuclear power plants should be safe, but this is far from the case, a prime example may serve as an accident at the Chernobyl nuclear power plant. In my opinion, any method of extracting energy (in any form) from the bowels of the Earth is a combination of positive and negative traits, and it seems to me that far from positive prevail.
I have not told about all directions of solving the energy problem by scientists of the world, but only about the main ones. Each country has its own characteristics: socio-economic and geographical conditions, provision with natural resources, the level of development of science and technology.
indicating the topic right now to find out about the possibility of obtaining a consultation.
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Competitive work
The role of chemistry in the energy sector: preparation of chemically demineralized water
ion exchange method for nuclear power plants
MOU gymnasium No. 3 named after.
, 10 "a" class
Leaders:
KNPP chemical shop laboratory assistant
- physics teacher, gymnasium No. 3
Contact phone numbers:
annotation
Kalinin NPP is the largest water consumer in the Udomelsky district.
This paper provides information on the requirements for the quality of drinking and circuit water. Comparative tables and histograms of chemical indicators of drinking, lake and water of the II circuit are given. given short description about the results of the visit to the water intake station and the chemical shop of the Kalinin NPP. A brief description of the theory of ion exchange and a description of the principal schemes of chemical water treatment and a block desalination plant are also given; a brief theoretical description of the principle of water purification from radioactive contamination - special water purification is also given.
This work helps to increase the motivation to study chemistry, physics, introduces the chemical technologies used in the energy sector on the example of the Kalinin NPP.
1.Introduction 3
2. Literature review on water treatment by method 4
ion exchange
2.1.Principle of NPP operation with VVER-1000 type reactors 4
2.2. Requirements for water used for
technological needs at NPP 5
2.3. Chemical indicators of the quality of natural and contour waters. 5
2.4 Theory of ion exchange 6
2.5 Working cycle of ion exchange resin 9
2.6.Features of the use of ion-exchange materials 10
3. Practical study 11
3.1.Visit to the water intake station 11
3.2.Visit to the Kalinin NPP 13
3.3. Description of the concept of chemical water treatment 15
3.4 Description of the circuit diagram
block demineralization plant 18
3.5. Theoretical description of the principle of operation
special water treatment 20
4.Conclusion 20
5. References 22
1. Introduction
1.1. Objective:
familiarization with the technology of water treatment for nuclear power plants by the ion exchange method and comparison of water quality: for technological needs of nuclear power plants, drinking and lake water.
1.2. Work tasks:
1. to study the requirements for water used for technological needs at a modern nuclear power plant using the example of the Kalinin nuclear power plant.
2. get acquainted with the theory of the ion exchange method,
3. visit the water intake station of Udomlya and get acquainted with chemical composition drinking water and lake water.
4. compare the indicators of chemical analysis of drinking water and water of the second circuit of the NPP.
5. visit the chemical shop of the Kalinin NPP and get acquainted with:
¾ with the process of water treatment at chemical water treatment;
¾ with the process of water purification at a block desalination plant;
¾ visit the express laboratory of the II circuit;
¾ get acquainted theoretically with the work of special water treatment.
6. draw conclusions about the importance of ion exchange in water treatment.
1.3. Relevance
Russia's energy strategy envisages nearly doubling electricity generation from 2000 to 2020. With predominant growth in nuclear energy: the relative share of electricity generation at nuclear power plants over this period should increase from 16% to 22%.
NPP equipment, like no other, is subject to safety, reliability and cost-effectiveness requirements.
One of the most important factors affecting the reliable and safe operation of nuclear power plants is compliance with the water chemistry regime and maintaining water quality indicators at the level of established standards.
The water chemistry regime of a nuclear power plant should be organized in such a way as to ensure the integrity of the barriers (fuel cladding, coolant circuit boundary, hermetic barriers, localizing safety systems) on the path of possible spread of radioactive substances into the environment. The corrosive effect of the coolant and other working media on the equipment and pipelines of NPP systems should not lead to violation of the limits and conditions of its safe operation. The water-chemical regime should ensure a minimum amount of deposits on the heat transfer surfaces of equipment and pipelines, as this leads to a deterioration in the heat transfer properties of the equipment and, as a result, to a reduction in the service life of the equipment.
2. Literature review on water treatment by ion exchange
2.1. The principle of operation of NPPs with VVER-1000 reactors
The principle of operation of most existing nuclear power plants is based on the use of heat released during the fission of the 235U nucleus under the action of neutrons. In the reactor core, under the action of neutrons, the 235U nucleus is split, releasing energy and heating the coolant - water.
Nuclear fuel transfers thermal energy to the primary coolant, which is water under high pressure (16 MPa), at the outlet of the reactor, the water temperature is 3200. Further, thermal energy is transferred to the secondary water. There is no direct contact between the coolant and the secondary circuit water. The coolant circulates in a closed loop: reactor - steam generator - main circulation pump - reactor. There are four such circuits. In the steam generator, the primary circuit coolant heats the secondary circuit water to vaporization. The steam enters the turbine, which rotates due to this steam. This steam is called the working fluid. The turbine is directly connected to an electric generator that generates electrical energy. Further, the exhaust steam with low pressure enters the condenser, where it is condensed due to cooling by lake water. Then additional cleaning and return to the steam generator. And so the cycle repeats: evaporation, condensation, evaporation.
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rice. 1. Technological scheme of a double-circuit NPP:
1 - reactor; 2 – turbogenerator; 3 - capacitor; 4 - feed pump; 5 – steam generator; 6 - main circulation pump.
2.2. Requirements for water used for technological needs at nuclear power plants
With the growth of steam and water parameters, the impact of water chemistry regimes increased. This led to an increase in the specific heat loads of the heating surfaces. Under these conditions, even slight deposits on the inner surfaces of the pipes cause overheating and destruction of the metal. High steam parameters (pressure and temperature) increase its dissolving power in relation to impurities contained in the feed water. As a result, the intensity of drifting of the flow part of the turbines increases, which can lead to a decrease in the efficiency of the units and, in some cases, to limit their power, and reduce the life of the equipment.
Elimination of shortcomings of water-chemical regimes is necessary not only for violations that create an emergency, but also for seemingly minor deviations from the norms. So, for example, from experience it follows that:
§ deposits of salts and corrosion products on the blades of the high-pressure cylinder of turbines of 300 MW units in the amount of 1 kg cause an increase in pressure in the turbine control stage by 0.5 - 1 MPa (5 - 10 kgf / cm2) and lead to a decrease in turbine power by 5 - 10 MW;
§ deposition of corrosion products on the inner and outer surfaces of the high-pressure heater pipes in the amount of 300–500 g/m2 reduces the feed water heating temperature by 2–30 °C and worsens the efficiency of the unit;
§ deposits in the steam-water path of blocks increase its hydraulic resistance and energy losses for pumping water and steam. An increase in the block path resistance of 300 MW per 1 MW (10 kgf/cm2) leads to an overexpenditure of 3 million kWh of electricity per year.
The following systems serve to meet the requirements for ensuring the water chemistry regime at nuclear power plants:
§ chemical water treatment;
§ system of condensation and degassing;
§ block desalination plant;
§ Installation of corrective treatment of the working environment of the primary and secondary circuits;
§ deaerators;
§ steam generator purge system;
§ steam generator blowdown water treatment unit (special water treatment);
§ system of purge-make-up of the primary circuit.
2.3. Chemical indicators of the quality of natural and contour waters
The water coolant for filling the energy circuits and their make-up is prepared from natural waters at water treatment plants of various types and usually contains the same impurities that characterize natural water, but at significantly lower (by several orders of magnitude) concentrations.
The main indicators of water quality include the following.
The content of coarse (suspended) substances , present in the loop waters - in the form of sludge, consisting of sparingly soluble compounds such as CaCO3 , CaSO4, Mg(OH)2, particles of corrosion products of structural materials (Fe3O4, Fe2O3, etc.), the content of which is determined by filtration through a paper filter with drying at C or by an indirect method by water transparency.
Salinity - the total concentration of cations and anions in water, calculated from the total ionic composition and expressed in milligrams per kilogram. To characterize and control waters and condensates with low salinity in the absence of dissolved CO2 and NH3 gases, the indicator is often used electrical conductivity . The condensate with a salt content of about 0.5 mg/kg has a specific electrical conductivity of 1 µS/cm.
Water hardness total - total calcium concentration ( calcium hardness) and magnesium ( magnesium rigidity), expressed in equivalent units of milligram equivalent per kilogram or microgram equivalent per kilogram:
ZHO \u003d ZhSa + ZhMg
Water oxidizability expressed by the consumption of a strong oxidizing agent (usually KMnO4) required for the oxidation of organic water impurities under standard conditions, and is measured in milligrams per kilogram of KMnO4 or O2, equivalent to the consumption of potassium permanganate.
Hydrogen concentration indicator ions (pH) of water characterizes the reaction of water (acidic, alkaline, neutral) and is taken into account in all types of water treatment and use.
Specific electrical conductivity (χ) is determined by the mobility of ions in a solution placed in an electric field; for pure water its value is 0.04 μS/cm, for demineralized turbine condensates χ = 0.1 μS/cm (microsiemens per centimeter).
2.4. Ion exchange theory
Preparation of water for filling the circuits of nuclear power plants and replenishing losses in them is carried out at the expense of demineralized water prepared by the method of chemical desalination in two or three stages of the initial low-mineralized water (Nitrogen "href="/text/category/azot/" rel="bookmark">nitrogen N and many other elements.Coal is practically insoluble in water, but when it comes into contact with oxygen dissolved in water, slow oxidation occurs, leading to the formation of various oxidized groups.On the surface of the coal, hydroxyl or carboxyl groups are formed, firmly bound to the base of the coal.If conditionally designate this unchanged base with the letter R, then the structure of such a material can be described by the formula ROH or RCOOH, depending on which oxidized group of the hydroxyl OH or carboxyl COOH formed on its surface during oxidation.These groups are capable of dissociation, i.e. in water processes occur in the environment:
RCOOH = RCOO - + H+.
If cations, for example, calcium, are present in water, then cation exchange processes become possible:
2RCOOH+Ca2+ = (RCOO)2Ca +2H+.
In this case, calcium ions are fixed on carbon, and an equivalent amount of hydrogen ions enters the solution. The exchange can also take place for other ions, such as sodium, iron, copper, etc.
2.4.2. Cation and anion exchangers.
All materials capable of cation exchange are called cation exchangers. Materials capable of anion exchange are called anion exchangers. They have other ion exchange groups, usually NH2 or NH, which form NH2OH with water.
Cation exchangers are able to exchange positively charged ions (cations) with the solution. The process of exchange of cations between the cation exchanger immersed in the water to be purified and this water is called cationization. Anion exchangers are capable of exchanging negatively charged ions with the electrolyte. The process of anion exchange between the anion resin and the treated water is called anionization.
On fig. 2 schematically shows the structure of ion exchanger grains. The grain practically insoluble in water is surrounded by dissociated grains - positively charged for the cation exchanger (Fig. 2a) and negatively charged for the anion exchanger (Fig. 2b). In the very grain of the ion exchanger, due to the separation of ions, a negative charge arises for the cation exchanger and a positive charge for the anion exchanger.
rice. 2. Scheme of the structure of ion exchanger grains.
a) – cation exchanger; b) - anion exchanger; 1- solid polyatomic framework of the ion exchanger; 2 – immobile ions of active groups bound to the framework (potential-forming ions); 3 - limitedly mobile ions of active groups capable of exchange (counterions).
Most of the currently used ion-exchange materials belong to the category of synthetic resins. Their molecules consist of thousands, and sometimes tens of thousands of interconnected atoms. Ion-exchange materials are a kind of solid electrolytes. Depending on the nature of the active groups of the ion exchanger, its mobile, exchangeable ions can have a positive or negative charge. When the positive, mobile cation is the hydrogen ion H+, then such a cation exchanger is essentially a polyvalent acid, just as an anion exchanger with an exchangeable hydroxyl ion OH - is a polyvalent base.
The mobility of ions capable of exchange is limited by distances at which their reciprocity with immobile ions of opposite charge on the surface of the ion exchanger is not lost. This space, bounded around the molecules of the ionite, in which there are mobile and exchangeable ions, is called the ionic atmosphere of the ionite.
The exchange capacity of ion exchangers depends on the number of active groups on the surface of the ion exchanger grains. The surface of the ion exchanger is also the surface of recesses, pores, channels, etc. Therefore, it is preferable to have ion exchangers with a porous structure. The grain size of domestic and foreign ion exchangers is characterized by fractions ranging from 0.3 to 1.5 mm with an average grain diameter of 0.5-0.7 mm and a heterogeneity coefficient of about 2.0-2.5.
There are ion exchangers in which almost all the functional groups contained in their composition or only a small percentage of them undergo dissociation, in accordance with which strong acid cation exchangers are distinguished - they are capable of absorbing cations (sodium Na +, magnesium Mg2 +, etc.); and weakly acidic - capable of absorbing hardness cations (magnesium Mg2+, calcium Ca2+). Similarly, the division into two groups of anion exchangers: strongly basic - capable of absorbing both strong and weak acids (for example, carbonic, silicic, etc.). and weakly basic - are capable of absorbing predominantly anion exchangers of strong acids (, etc.).
2.5. Working cycle of ion exchange resin
The layer of ion exchanger (ion exchange resin) in the course of movement of the treated water in the process of ion exchange can be divided into three zones.
The first zone is the zone of depleted ion exchanger, since all the counterions in it are used for exchange for ions of the treated water. In this zone, the selective exchange between the ions of the treated water itself continues, i.e., the most mobile ions contained in the water displace the less mobile ones from the ion exchanger (Fig. 3).
The second zone is called the useful exchange zone. Here begins and ends the useful exchange of ion exchanger counterions for treated water ions. In this zone, the frequency of exchange of treated water ions for counterions of the ion exchanger prevails over the frequency of the reverse exchange of treated water ions and ions absorbed by the ion exchanger.
The third zone is the zone of idle, or fresh, ion exchanger. The water passing through this layer of the ion exchanger contains only the counterions of the ion exchanger and therefore does not change either its composition or the composition of the ion exchanger.
As the filter operates, the first zone - the zone of depleted ion exchanger - increases, forcing the operating zone 2 to fall due to the reduction of the zone of fresh ion exchanger 3, and, finally, goes beyond the lower boundary of the filter load. Here the height of the third zone is zero. The concentration of the least sorbed ions appears in the filtrate and begins to increase, and the useful work of the ion-exchange filter ends.
Technology of the regeneration process.
The process of regeneration of ion exchange filters consists of three main operations:
Loosening of the ion exchanger layer (loose washing);
Passing through it the working solution of the reagent at a given speed;
Washing the ion exchanger from regeneration products.
Loose wash.
During the operation of filters, products of gradual destruction and grinding of ion exchangers always occur, which must be periodically removed. This is achieved by loosening washes, this operation is mandatory before each regeneration.
It is very important to observe the conditions for washing, which should ensure a more complete removal of fine dust-like parts of ion-exchange materials from the filter. In addition, the loosening washing eliminates the compaction of the material, which makes it difficult for the regeneration solution to contact with the grains of the ion exchanger.
Loosening is carried out by a flow of water from the bottom up at a speed that brings the entire mass of the ion-exchange material into suspension. When the water at the outlet of the filter becomes transparent, loosening is stopped.
Passing the regeneration solution.
Regeneration and washing of the ion exchanger from the products of regeneration are usually carried out at the same speed. The passage of reagents in this case is possible both along the treated water - forward flow, and in the opposite direction to the movement of the treated water - countercurrent, depending on the technology adopted.
When regeneration solutions are skipped, the ions absorbed by the ion exchanger are replaced by ions of the regeneration solution (containing H+ or OH - ion). At the same time, ionites are transferred to their original ionic form.
There are two types of regeneration: internal and external. Remote regeneration is used in mixed-bed filters on a block desalination plant in order to avoid regeneration water from entering the secondary circuit.
Washing out the remnants of regeneration products.
The last operation of the regeneration cycle - washing - is intended to remove the remnants of regeneration products from it.
The washing of the filter layer is stopped when certain indicators of the quality of the washing water are reached. The filter is ready for use.
These processes allow the ion exchanger to be used repeatedly.
2.6. Features of the use of ion-exchange materials at nuclear power plants
The removal of radionuclides from water by the ion exchange method is based on the fact that many radionuclides are in water in the form of ions or colloids, which, when in contact with the ion exchanger, are also absorbed by the filter material, but absorption is of a physical nature. The volumetric capacity of resins in relation to colloids is much lower than in relation to ions.
The completeness of the absorption of radionuclides by ion exchangers is affected by the content of a large number of inactive elements in water, which are chemical analogues of radionuclides.
Under conditions of ionizing radiation, only highly pure ion exchangers in hydrogen and hydroxyl form (strong base anion exchangers and strong acid cation exchangers) are used. This is due to the insufficient resistance of ion-exchange materials to the action of ionizing radiation and more stringent requirements for the water regime of the NPP primary circuit.
3. Practical research
3.1. Visit to the water intake station
In 1980, the first stage of the Udomlya water intake station was put into operation. The main task, which is the extraction and preparation of water for consumer needs. Water from artesian wells is pumped for purification, which includes: aeration and filtration. Then the water is chlorinated and served to consumers.
On December 14, 2007, an excursion to the water intake station took place in order to get acquainted with the processes: water preparation, determination of the main indicators of the quality of drinking and lake water.
Determination of pH solutions on a pH meter at a water intake station.
Preparation of samples for the determination of iron on the KFK-3 photocolorimeter.
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Determination of chlorides by back titration.
Determination of hardness salts.
The data obtained in the course of joint research with the employees of the water intake are given in the tables.
Table 1. Comparison of quality indicators of lake water (using the example of Lake Kubycha) and drinking water.
Index | unit of measurement | lake water | Drinking water | |
lake Kubycha |
||||
Chroma | ||||
Turbidity | ||||
Rigidity | ||||
Mineralization | ||||
MPC* - maximum permissible concentration - is regulated by GOST of water quality.
Histogram 1. pH value of Kubycha Lake, drinking water and maximum allowable concentration.
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Histogram 3. The content of hardness salts in Lake Kubycha, drinking water and the maximum allowable concentration.
On December 25" href="/text/category/25_dekabrya/" rel="bookmark"> On December 25, 2007, an excursion to the Kalinin Nuclear Power Plant took place in order to get acquainted with the work of the chemical department units. During the visit to the machine room, they got acquainted with the technology of purification of the main condensate of the second circuit, with the work of the express laboratory of the second circuit, and received data on the quality of the water of the second circuit.
It is interesting to compare some chemical indicators of the quality of water in the secondary circuit of the Kalinin NPP and drinking water obtained at the water intake.
Table 2. Comparative characteristics of drinking water and water of the second circuit of the NPP.
* - data are not indicated, since the concentration of hardness is less than the sensitivity of the method for determining this indicator.
Conclusion: 1. As follows from Table 2, the maximum permissible concentration drinking water and control values of secondary water have significant differences. This is due to the higher requirements for water used for process needs, necessary for the safe and reliable operation of the equipment.
2. Drinking water obtained at the water intake is of high quality, chemical indicators are significantly below the maximum permissible concentration impurities in drinking water.
3. Water of the second circuit corresponds to the control values. This is achieved by purifying water by ion exchange during its preparation and post-treatment of condensate at block desalination plants.
Histogram 4. The content of chlorides in drinking water and water of the secondary circuit of the Kalinin NPP.
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High requirements for the content of hardness salts in the water of the secondary circuit are caused by the fact that scale-forming salt deposits appear on the walls of the heat exchangers. This leads to: worsening of heat transfer, reduction of hydraulic resistance, reduction of equipment service life.
Histogram 6. Iron content in drinking water and secondary water.
Cooling systems" href="/text/category/sistemi_ohlazhdeniya/" rel="bookmark">cooling systems for generator stator windings, electrolysis tanks, special laundry. Productivity of chemical water treatment for demineralized water = 150m3.
Description of the main technological scheme of the desalination part of chemical water treatment.
The clarified water after the mechanical pre-filter enters the chain of H-cation exchange filters. In the H-cationite filter of the 1st stage, loaded with a weakly acidic cation exchanger, water is purified from cruelty ions (Сa2+ and Mg2+). In the H-cationite filter of the 2nd stage, loaded with a strongly acidic cation exchanger, water is additionally purified from the hardness ions and Na + ions remaining after the 1st stage.
H-cation exchange water after the 2nd stage is collected in tanks of partially demineralized water of the cation exchange filter.
From the tank of partially demineralized water, pumps direct the water to a chain of OH-anion-exchange filters. In the OH-anion filter of the 1st stage, loaded with a low-basic anion exchanger, water is purified from anions of strong acids (https://pandia.ru/text/77/500/images/image010_45.gif" width="37" height=" 24 src=">). In the OH-anion filter of the 2nd stage, loaded with a highly basic anion exchanger, water is additionally purified from the anions of strong acids and anions of weak acids remaining after the 1st stage (; ).
OH-anioned water after the 2nd stage anion exchange filter is collected in the auxiliary tank.
The desalinated water from the auxiliary tank is pumped to the 3rd stage of desalination - a mixed-bed filter. The mixed bed filter is loaded with a 1:1 mixture of strong acid cation and strong base anion. At the 3rd stage of desalination, the demineralized water is additionally purified from cations and anions to the concentrations required by the standard of the STP-EO enterprise. On the common pipeline, chemically desalinated water after the mixed-action filter is equipped with 2 parallel-connected traps of filtering materials (1 - in operation; 1 - in reserve in case of repair of the first one) of chemically desalinated water from the auxiliary tank and after the mixed-action filter is issued to consumers: for make-up 2 -th circuit to the turbine hall; for feeding the 1st circuit into a special building; to the pre-treatment scheme of chemical water treatment, to the chemical reagent warehouse, to the special laundry, to the electrolysis, to the start-up and reserve boiler house, to the storage tanks of chemically desalted water (V = 3000 m3).
To increase the reliability of the chemical water treatment and create a supply of chemically demineralized water, chemically demineralized water storage tanks (3000 m3 each) are included in the scheme of the demineralizing part of chemical water treatment.
To prevent corrosion of metal pipelines in concentrated and dilute acid solutions, the piping of the concentrated acid unit and the route for supplying the regenerating acid solution from the mixer to the H-cation exchange filters are made of pipelines lined with fluoroplastic.
Commissioning" href="/text/category/vvod_v_dejstvie/" rel="bookmark"> was put into operation in August 2007, the service life is about 20 years, the effluent distribution radius is about 3 km.
Thus, it can be concluded that the commissioning of a deep disposal site excludes the possibility of discharging industrial non-radioactive effluents into the environment.
3.4. Description of the block diagram of a block desalination plant (condensate treatment)
Condensate treatment at the block desalination plant is carried out in two stages:
The first step is cleaning from undissolved corrosion products of structural materials on electromagnetic filters loaded with steel soft magnetic balls;
The second step is cleaning from dissolved ionic impurities and colloidal-dispersed substances on mixed-action ion-exchange filters.
Turbine condensate is supplied by condensate pumps of the first stage to an electromagnetic filter, where it is cleaned of mechanical impurities, mainly undissolved corrosion products of structural materials.
After the electromagnetic filter, the condensate enters the suction manifold of the condensate pumps of the second stage (with the ion-exchange part of the block desalination plant turned off), or is sent to a mixed-action filter for purification from dissolved and colloidal-dispersed impurities.
Removal of ferromagnetic and non-magnetic iron oxides retained on the ball load is carried out by washing the electromagnetic filter with demineralized water from the bottom - up with the voltage removed on the coils and the demagnetized state of the balls.
In case of unsatisfactory quality of the condensate downstream of the operating mixed-bed filter, the filter is taken out for regeneration, and the backup mixed-bed filter is put into operation.
The mixed resin brought out for regeneration is reloaded into the filter-regenerator, where it is hydraulically divided into cation exchanger and anion exchanger. To transfer the cation exchanger and anion exchanger into a working form, they are regenerated.
Fig.5. Scheme of a block desalination plant.
EMF - electromagnetic filter; FSD - mixed action filter; LFM is a trap of filter materials.
All regenerative waters are supplied to radiation control tanks and after radiation control, if the established levels are not exceeded, they are pumped out to chemical water treatment neutralizer tanks.
After each mixed-action filter, filters are installed - traps of ion exchangers.
During a visit to the Kalinin NPP, the following data were obtained on the operation of the block desalination plant:
100% of condensate is passed through electromagnetic filters, it is possible to pass through a mixed-action filter both 100% of water and part of it. Thus, with one operating mixed-action filter (purification of 20% of the condensate), the specific electrical conductivity decreased: χ=0.23 µS/cm - before the block desalination plant and χ=0.21 µS/cm - after the block desalination plant.
3.5. Theoretical description of the principle of operation of a special water treatment
Ion-exchange filters of the primary circuit, as a rule, operate continuously, and they branch off approximately 0.2 - 0.5% of the main water flow in the circuit.
Primary circuit water is purified at a special water treatment plant, which consists of a mixed-bed filter. It serves both to remove corrosion products from reactor water and to regulate the physicochemical composition of water (normalized indicators are maintained). A special water purification plant improves the radiation situation by reducing the radioactivity of the coolant by one or two orders of magnitude.
The circulation water of the primary circuit is supplied to the special water treatment plant from the main circulation pump and is returned to the circuit after cleaning.
In the mixed bed for the treatment of radioactive water, ion exchangers are used at a ratio of cation exchanger and anion exchanger equal to 1:1 or 1:2.
A homogeneous mixture of ion exchangers (charge) makes it possible to remove contaminants from the loop water that accidentally enter during poor-quality washing from the reagents of the filters of the installations associated with feeding the loop, as well as from the decomposition products of ion-exchange materials under the action of ionizing radiation and high temperature.
When depleted, the ion exchangers of special water treatment plants are regenerated: cation exchanger - nitric acid(at the same time it is converted into the H-form), anion exchanger - with caustic soda or caustic potash (translated again into the OH-form).
Conclusion
Having studied the materials on the technology of energy production at NPPs with VVER-1000 reactors, we came to the conclusion that one of the most important factors for the reliable operation of NPPs is high-quality treated water. This is achieved through the use of various physical and chemical methods of water purification, namely through the use of preliminary treatment - clarification and deep desalination by ion exchange.
The visit to the water intake station made a special impression, namely, the performance of chemical analyzes using instruments and equipment that are not used at school. This increased confidence in the quality of drinking water supplied by the water intake station for the needs of the city. But the quality parameters of the water used at the Kalinin NPP made a greater impression. Of great interest were the technological processes of water treatment in the chemical workshop, which they got acquainted with during a visit to the Kalinin NPP.
Water treatment by ion exchange allows reaching the required values necessary for the safe, reliable and economical operation of the equipment. However, this is a rather expensive process: the cost of 1 m3 of chemically desalted water is 20.4 rubles, and the cost of 1 m3 of drinking water is 6.19 rubles. (data from 2007).
In this regard, there is a need for a more economical use of chemically demineralized water, for which closed water circulation cycles are used. To maintain the required water parameters (removal of incoming impurities), condensate cleaning (on the second circuit) and special water treatment (on the first circuit) are used. The presence of closed cycles prevents the discharge of water from the primary and secondary circuits into the environment, and for industrial effluents there is a system of neutralization and utilization, which reduces the technogenic load.
Despite the fact that the material presented in the project goes beyond the scope of the school curriculum, acquaintance with it motivates high school students to study chemistry more deeply, as well as make an informed choice of a future profession related to nuclear energy.
Bibliography.
1., Senin - technological modes of NPP with VVER: Tutorial for universities. - M.: MPEI Publishing House, 2006. - 390 p.: ill.
2., Martynov regime of nuclear power plants. - M.: Atomizdat, 1976. - 400 p.
3. Mazo water ion exchangers. - M.: Chemistry, 1980. - 256 p.: ill.
4. , Kostrikin water treatment. – M.: Energoizdat, 1981. – 304 p.: ill.
5., Zhgulev energy blocks. – M.: Energoatomizdat, 1987. – 256 p.: ill.
6., Churbanova water quality: Textbook for technical schools. - M.: Stroyizdat, 1977. - 135 p.: ill.
Energy of the chemical industry occupies one of the main places in the modern industry. Without her participation, it would be impossible to carry out technological processes. Energy is used to a large extent to ensure human life.
There are different types of energy:
- electric;
- thermal;
- nuclear and thermonuclear;
- light;
- magnetic;
- chemical;
- mechanical.
Absolutely all chemical industries consume energy. The processes of the industry are associated either with the use or with the mutual circulation of energy. Electrical energy is used for electrochemical, electrothermal and electromagnetic processes. These are electrolysis, melting, heating, synthesis. For the processes of grinding, mixing, operation of compressors and fans, the conversion of electrical energy into mechanical energy is used.
For the flow of physical processes that are not accompanied by heating, melting, distillation, drying, that is, chemical reactions, thermal energy is used. Chemical energy is used in galvanic devices, where it is converted into electrical energy. Light energy is used to carry out photochemical reactions.
Fuel base of energy for the chemical industry
AT energy chemical industry fossil fuels and their derivatives are the main source of energy consumption. The energy intensity of production is determined by the energy consumption per unit of manufactured products.
Energy includes the extraction of energy resources (oil, gas, coal, shale) and their processing, as well as special modes of transport. These include oil pipelines, gas pipelines, power lines and product pipelines.
The fuel energy sector is also a raw material base for the petrochemical and chemical industries. All its products are heat treated to isolate individual components (eg coke from coal, ethane, ethylene, butane, propane from oil and gases). Only natural gas is used in its pure form for the production of chemical products such as ammonia, methyl alcohol.
The energy industry is developing dynamically and rapidly, provoking the development scientific and technological progress. The demand for the use of energy resources is growing more and more, in connection with this, the search for deposits and the creation of new industries are priority components of the industry. However, this area leads to numerous problems in the economy, politics, geography, ecology, which are of a global nature.
The most developing segments of the energy sector are the oil and oil refining, as well as the gas industries. The extraction of natural resources occupies a significant place in the world, and their deposits sometimes give rise to conflicts between states. Oil is an important energy carrier; after its processing, a lot of products necessary for human activity are obtained. Their list includes kerosene, gasoline, different kinds fuels and petroleum oils, fuel oil, tar and others. The need for the oil refining industry arose with the development of transport and aviation to provide it with fuel. The gas industry is the most progressive and promising area. Natural gas is the main raw material for chemical production and its use is very different.
The exhibition "Chemistry" in the fall in a large volume and scale will present the latest technology and developments in the field energy chemical industry. At this exhibition, manufacturers and consumers can not only get acquainted with the goods and assortment, but also conclude new deals, establish relationships with both domestic and foreign partners. According to experts, "Chemistry" has a huge impact on the development and promotion of new technologies. In addition, it highlights not only new methods and achievements in science and technology, but also means of individual and collective protection at work.
The exhibition, organized by the Expocentre Fairgrounds, has been held in Moscow since 1965. And Expocentre specialists allow holding such events on the very high level. Therefore, it is repeatedly chosen as the venue for such events by both domestic and foreign organizers.
Chemical reactions are accompanied by the release or absorption of energy. If energy is released or absorbed in the form of heat, then such reactions are written using the equations of chemical reactions indicating thermal effects, while it is necessary to indicate the phase composition of the reacting substances.
chemical reactions, flowing with the release of heat, are called exothermic, and with the absorption of heat - endothermic.
Thermochemistry is the study of the thermal effects of reactions. In thermochemistry, the thermal effect of a reaction is denoted by Q and is expressed in kJ.
Thermochemistry is one of the sections of chemical thermodynamics that studies the transitions of energy from one form to another and from one set of bodies to others, as well as the possibility, direction and depth of the implementation of chemical and phase processes under given conditions. Each individual substance or their combination is a thermodynamic system. If the thermodynamic system does not exchange with environment neither matter nor energy, it is called isolated. Such an idealized system is used as a physical abstraction when considering processes that exclude the influence of the external environment. A system that exchanges only energy with the environment is called a closed system. If energy and material exchange is possible, the system is open.
The state of the system is determined by the thermodynamic parameters of the state - temperature, pressure, concentration, volume, etc. The system is characterized, in addition, by such properties as internal energy U,enthalpy H, entropy S, Gibbs energy G. Of the change in the course of chemical reactions characterize its energy system.
Internal energy of the system U consists of the energy of motion and interaction of molecules, the energy of binding in molecules, the energy of motion and interaction of electrons and nuclei, etc.
The absolute value of the internal energy cannot be determined, but its change during the transition of the system from the initial state to the final state as a result of the implementation of a chemical process can be calculated. If the system receives a certain amount of heat at a constant pressure Qp, the latter is spent on changing the internal energy of the system ΔU and doing work A = PΔV against external forces:
This equation expresses the law of conservation of energy or the first law of thermodynamics.
adiabatic process is a process of quasi-static expansion or compression of a gas in a vessel with heat-impermeable walls. The first law of thermodynamics for an adiabatic process takes the form:
Isothermal process is a process of quasi-static expansion or contraction of a substance in contact with a thermal reservoir (T = const).
Since the internal energy of an ideal gas depends only on temperature (Joule's law), the first law of thermodynamics for an isothermal process is written as: Q = A.
In an isochoric process (V = const), the absorption or release of heat (thermal effect) is associated only with a change in internal energy:
In chemistry, isobaric processes (P = const) are most often considered, and the thermal effect in this case is called the change in the enthalpy of the system or the enthalpy of the process:
∆H = ∆U + P∆V
Enthalpy has the dimension of energy (kJ). Its value is proportional to the amount of substance; the enthalpy of a unit amount of a substance (mol) is measured in kJ ∙ mol -1.
In a thermodynamic system, the released heat of a chemical process is considered to be negative (exothermic process, ΔH< 0), а поглощение системой теплоты соответствует эндотермическому процессу, ΔH > 0.
The equations of chemical reactions indicating the enthalpy of the process are called thermochemical. The numerical values of the enthalpy ΔH are indicated, separated by commas, in kJ and refer to the entire reaction, taking into account the stoichiometric coefficients of all reactants.
Since the reactants can be in different states of aggregation, it is indicated by the lower right index in brackets: (t) - solid, (k) - crystalline, (g) - liquid, (d) - gaseous, (p) - dissolved.
For example, when gaseous H 2 and Cl 2 react, two moles of gaseous HCl are formed. The thermochemical equation is written as follows:
When gaseous H 2 and O 2 interact, the resulting H 2 O can be in three states of aggregation, which will affect the change in enthalpy:
The given enthalpies of formation (reactions) are referred to standard conditions of temperature and pressure (T = 298 K, P = 101.325 kPa). The standard state of a thermodynamic function, such as enthalpy, is indicated by subscripts and superscripts: ΔΗ 0 298 The subscript is usually omitted: ΔΗ 0 .
The standard enthalpy of formation ΔΗ 0 arr is the thermal effect of the reaction of formation of one mole of a substance from simple substances, its components, which are in stable standard states. The enthalpy of formation of simple substances is assumed to be zero.
Using tabular values ΔΗ 0 arr, ΔΗ 0 burn, it is possible to calculate the enthalpies of various chemical processes and phase transformations.
The basis for such calculations is the Hess law, formulated by the St. Petersburg professor G. I. Hess (1841):
"The thermal effect (enthalpy) of the process depends only on the initial and final state and does not depend on the path of its transition from one state to another."
The following consequences follow from Hess's law:
1. The enthalpy of the reaction is equal to the difference between the sums of the enthalpies of formation of the final and initial participants in the reactions, taking into account their stoichiometric coefficients.
ΔH = ΣΔH return end – ΣΔH return start
2. The enthalpy of the reaction is equal to the difference between the sums of the enthalpies of combustion of the initial and final reactants, taking into account their stoichiometric coefficients.
ΔH = ΣΔH combustion start – ΣΔH combustion final
3. The enthalpy of the reaction is equal to the difference between the sums of the bond energies Eb of the initial and final reagents, taking into account their stoichiometric coefficients.
In the course of a chemical reaction, energy is expended on the destruction of bonds in the initial substances (ΣE ref) and is released during the formation of reaction products (–ΣE prod).
ΔH° = ΣE ref – ΣE cont
Consequently, exothermic effect of the reaction indicates that compounds with stronger bonds than the original ones are formed. When endothermic reaction on the contrary, the starting materials are stronger.
4. The enthalpy of the formation reaction of a substance is equal to the enthalpy of the reaction of its decomposition to the starting substances with the opposite sign.
ΔH arr = –ΔH decom
5. The enthalpy of hydration is equal to the difference between the enthalpies of dissolution of an anhydrous salt ΔH sol b/s and crystalline hydrate ΔH sol crist.
Hess's law allows one to treat thermochemical equations as algebraic ones, i.e., to add and subtract them if the thermodynamic functions refer to the same conditions.