Gases have a number of properties that make them indispensable in a very large number of technical devices.
Gas is a shock absorber. The high compressibility and lightness of gas, the ability to regulate pressure, make it one of the most advanced shock absorbers used in a number of devices.
This is how a car or bicycle tire works. When the wheel hits a tubercle, the air in the auger is compressed and the push received by the wheel axle is significantly softened (Fig. 35). If the tire were rigid, the axle would jump up to the height of the tubercle.
Gas is the working fluid of engines. High compressibility and a strong dependence of pressure and volume on temperature make the gas an indispensable working fluid in engines running on compressed gas and in heat engines.
In engines running on compressed gas, such as air, the gas, when expanding, does work at almost constant pressure. Compressed air, exerting pressure on the piston, opens doors on buses and electric trains. Compressed air powers the air brake pistons of railway cars and trucks. Pneumatic hammer and others pneumatic tools set in motion compressed air. Even on spaceships There are small jet engines running on compressed gas - helium. They orient the ship in the desired way.
Internal combustion engines in cars, tractors, airplanes and jet engines use high-temperature gases as the working fluid that drives the piston, turbine or rocket. When the combustible mixture burns in the cylinder, the temperature sharply increases to thousands of degrees, the pressure on the piston increases and the gas, expanding, does work along the length of the piston’s working stroke (Fig. 36).
Only gas can be used as a working fluid in heat engines. Heating liquid or solid to the same temperature as the gas would cause only a slight movement of the piston.
Any firearm is essentially a heat engine. The pressure force of gases - products of combustion of explosives - pushes a bullet out of the barrel bore or a projectile out of the barrel of a gun. And it is important that this force does work along the entire length of the channel. Therefore, the speeds of the bullet and projectile are enormous - hundreds of meters per second.
Rarefied gases. The ability for unlimited expansion leads to the fact that obtaining gases at very low pressures - in a vacuum state - is a complex technical task. (In a state of vacuum, gas molecules practically do not collide with each other, but only with the walls of the vessel)
Conventional piston pumps become ineffective due to gas leakage between the piston and the cylinder walls. With their help, it is not possible to obtain pressure below tenths of a millimeter of mercury. Must be used for pumping out gases complex devices. Currently, pressures of the order of Pa mmHg have been achieved. Art.).
Vacuum is needed mainly in vacuum tubes and other electronic devices. Collisions electrically
charged particles (electrons) with gas molecules interfere with the normal operation of these devices. Sometimes it is necessary to create a vacuum in very large volumes, for example in particle accelerators.
Vacuum is also needed for smelting impurity-free metals, creating thermal insulation, etc.
1. What is called the equation of state? 2. Formulate an equation of state for an arbitrary mass of an ideal gas. 3. What is the universal gas constant? 4. How are the pressure and volume of a gas related in an isothermal process? 5. How are volume and temperature related in an isobaric process? 6. How are pressure and temperature related in an isochoric process? 7. How can isothermal, isobaric and isochoric processes be carried out? 8. Why are only gases used as a working fluid in heat engines?
Ideal gas is a physical model of a real gas, representing
is a collection of a large number of material points, between which
There is no interaction between us. This model neglects two properties of a real gas:
1) the presence of the own sizes of atoms and molecules; they count material points;
2) the presence of interaction between particles (attraction at large
distances and repulsion at small)
As a consequence of these neglects real gases obey the ideal gas laws only when:
1) low densities or concentrations, when the sizes of molecules and their interactions can be neglected;
2) at temperatures significantly higher than the temperature of gas liquefaction, when the kinetic energy is significantly greater than the potential energy of attraction.
The equation of state of an ideal gas relates the main thermodynamic parameters of the gas.
Two equations of state were obtained experimentally for an ideal gas: caloric And thermal.
The caloric equation relates the internal energy of a gas to temperature:
Where With– experimental constant.
Thermal equation – Mendeleev-Clapeyron equation.
An equation establishing the relationship between pressure, volume and absolute temperature of gases was obtained by the French physicist B. Clapeyron (1799-1864). In the shape of:
it was first used by the great Russian scientist D.I. Mendeleev, therefore the equation of state of a gas is called Mendeleev-Clapeyron equation.
The Mendeleev equation can be written through other thermodynamic parameters:
1
Because 
, That 
.
2
Considering that 
, That 
.
3
By definition of density 
, hence 
.
4
By definition of concentration 
, Then 
, 
, Then:
– basic MKT equation,
Where 
– Boltzmann’s constant, which relates energy and temperature.
The equation Mendeleev-Clapeyron valid only for ideal gases.
Mendeleev-Clapeyron equation for a constant mass of gas will be written as:
.
Exact value the constant on the right side of this equation depends on the amount of gas. If the amount of gas is equal to one mole, then the corresponding constant is denoted by the letter R and is called the universal gas constant:
.
This equation is called ideal gas equation of state. It was obtained in 1834 by the French physicist and engineer B. Clapeyron. The universal gas constant is also called the gas constant:
.
For any, but constant, gas mass from the equation Mendeleev-Clapeyron we obtain a generalized gas law: the ratio of the product of gas pressure and volume to its temperature is a constant value for a constant gas mass:
.
Isothermal process– the process of changing the state of a gas at a constant temperature: Τ = const. To implement this, a vessel with a piston filled with gas must be brought into contact with the thermostat, i.e. a body of such large mass that it ensures a constant temperature of the gas, even when it gives off or receives some heat from the gas.
at constant temperature the dependence is obtained
or 
.
which describes the Boyle-Mariotte law: at a constant temperature, constant mass and constant chemical composition of a gas, the product of pressure and volume is a constant value.
Graphs of the relationship between the parameters of a given mass at a constant temperature are called isotherms. In Fig. 1.1 shows isotherms in ko
| T 2 >T 1 |
Boyle-Mariotte Law- one of the fundamental gas laws, discovered in 1662 by Robert Boyle (1627-1691) and independently rediscovered by Edme Mariotte (1620-1684) in 1676.
It is important to clarify that in this law gas is considered as ideal. In fact, all gases differ to one degree or another from ideal. The higher the molar mass of the gas, the greater this difference.
Isobaric process– the process of changing the state of a gas at constant pressure: p = const.
A quantitative study of the dependence of gas volume on temperature at constant pressure was carried out in 1802 by the French physicist and chemist Joseph Louis Gay-Lussac (1778-1850).
From the generalized gas law
at constant pressure the dependence is obtained
or 
,
which describes Gay-Lussac's law: the volume of a given mass of gas at constant pressure and constant chemical composition is directly proportional to the absolute temperature.
Graphs of the dependence between gas parameters at constant mass gas and pressure are called isobars(Fig. 1.2).
| p 1 |
| p |
| T |
| p 1 |
| p 2 |
| V |
| p |
| p 1 |
| p 2 |
Gay-Lussac's law can be written in terms of temperature t
,
Where V 0 – volume of gas at 0 °C, α = 1/273 K -1– temperature coefficient of volumetric expansion, which turned out to be the same for all gases.
Isochoric process– the process of changing the state of a gas at a constant volume: V = const. Experimentally, the dependence of gas pressure on temperature at constant volume was established in 1787 by the French physicist Jacques Charles (1746-1823) and refined by J.L. Gay-Lussacôme in 1802.
From the generalized gas law
at a constant volume the dependence is obtained
or 
,
which describes Charles's law or Gay-Lussac's second law: the pressure of a given mass of gas at a constant volume and constant chemical composition is directly proportional to the absolute temperature.
Charles's law or Gay-Lussac's second law can be written in terms of temperature t, measured on the Celsius scale:
,
Where R 0 – volume of gas at 0 °C, β = 1/273 K -1– temperature coefficient pressure, the same for all gases.
| V 1 |
| V |
| T |
| V 1 |
| V 2 |
| V |
| p |
| p 1 |
| p 2 |
To explain the properties of matter in the gaseous state, the ideal gas model is used. Ideal It is considered gas if:
a) there are no attractive forces between molecules, i.e. molecules behave like absolutely elastic bodies;
b) the gas is very discharged, i.e. the distance between the molecules is much more sizes the molecules themselves;
V) thermal equilibrium throughout the entire volume is achieved instantly. The conditions necessary for a real gas to acquire the properties of an ideal gas are met under the appropriate rarefaction of the real gas. Some gases even with room temperature and atmospheric pressure differ slightly from ideal.
The main parameters of an ideal gas are pressure, volume and temperature.
One of the first and important successes MCT was a qualitative and quantitative explanation of gas pressure on the walls of a vessel. Qualitative the explanation is that gas molecules, when colliding with the walls of a vessel, interact with them according to the laws of mechanics as elastic bodies and transfer their impulses to the walls of the vessel.
Based on the use of the basic principles of molecular kinetic theory, the basic MKT equation for an ideal gas was obtained, which looks like this: p = 1/3 t 0 pv 2 .
Here R - ideal gas pressure, m 0 -
molecular mass, P - concentration of molecules, v 2 - the mean square of molecular speed.
Denoting the average value of the kinetic energy of the translational motion of ideal gas molecules E k, we obtain the basic equation of MKT of an ideal gas in the form: p = 2/3nE k .
However, by measuring only gas pressure, it is impossible to know either the average kinetic energy of individual molecules or their concentration. Consequently, to find the microscopic parameters of a gas, it is necessary to measure some other physical quantity related to the average kinetic energy of the molecules. Such a quantity in physics is temperature. Temperature - scalar physical quantity, describing the state of thermodynamic equilibrium (a state in which there is no change in microscopic parameters). As a thermodynamic quantity, temperature characterizes the thermal state of the system and is measured by the degree of its deviation from what is assumed to be zero; as a molecular-kinetic quantity, it characterizes the intensity of the chaotic movement of molecules and is measured by their average kinetic energy.
E k = 3/2 kT, Where k = 1.38 10 -23 J/K and is called Boltzmann constant.
The temperature of all parts of an isolated system in equilibrium is the same. Temperature is measured by thermometers in degrees of various temperature scales. There is an absolute thermodynamic scale (the Kelvin scale) and various empirical scales that differ in their starting points. Before the introduction of the absolute temperature scale, the Celsius scale was widely used in practice (the freezing point of water is taken to be 0 °C, and the boiling point of water at normal atmospheric pressure is taken to be 100 °C).
2. Electric current in solutions and melts of electrolytes. Law of electrolysis. Application of electrolysis in technology.
Substances that conduct electricity are called electrolytes. Change chemical composition solution or melt when an electric current passes through it. Caused by the loss or gain of electrons by ions, it is called electrolysis.
Michael Faraday found that when passing el. current through the electrolyte, the mass of substance m released on the electrode is proportional to the charge q passing through the electrolyte:
m=k*q or m=k*I*t.
The dependence obtained by Faraday is called the law of electrolysis. The proportionality coefficient k is called the electrochemical equivalent.
k=1/e*N a * M/n ==> m=1/e*N a * M/n *I *t.
The coefficient k is numerically equal to the mass of the substance released on the electrodes during the transfer of 1 C charge by ions:
k=m/q; [k]=kg/Cl.
The product of the electron charge and Avogadro's number is called the Faraday number: 96500 C/mol.
Faraday number is electric charge, transferred by a substance in an amount of 1 mol during electrolysis.
IN electric field The electrolyte ions begin to move: positive ions move towards the cathode, and negative ions towards the anode. This creates an electric current in the electrolyte. When positive and negative ions meet, they combine - recombination.
Many metals are obtained from salts and oxides using electrolysis. The electrolytic method makes it possible to obtain substances with a small amount of impurities. By electrolysis, thin layers of metals can be deposited; these layers can serve to protect the product from oxidation. This method is called galvanostegy.
When current is passed for a long time, a thick layer of metal is obtained, which can be separated while maintaining its shape - electroplating. The phenomenon of electrolysis underlies the operating principle of acid and alkaline batteries, which use the reversibility of the electrolysis process.
Lesson in 10th grade “Use of gases in technology”
Target: Study the properties of gases and their use in technology
Objectives: educational:
developing:
educational
During the classes
Organizational moment
Examination homework(test)
Organizing student work in groups
Group performance
Homework
Test
1. The amount of a substance is measured in:
A. molecules
V. atoms
G. kilograms
E. kg/mol
2. Molar mass is:
A. mass of substance
B. mass of one mole of a substance
B. relative molecular weight
G. mass of one molecule (one atom)
D. amount of substance
E. 1/12 the mass of a carbon atom
3. Avogadro’s constant is numerically equal to:
4. The constant in the Clapeyron equation is called:
A. Avogadro's constant
B. Boltzmann constant
B. universal gas constant
G. absolute temperature
D. amount of substance
E. molar mass
5. For an isothermal process:
A. as pressure increases, volume decreases
B. when pressure increases, volume increases
B. pressure and volume do not change
D. when pressure decreases, volume decreases
D. as temperature increases, volume increases
E. as volume increases, temperature decreases
6. Avogadro’s constant is:
A. mass of one mole of a substance
B. number of molecules per unit volume of a substance
B. the number of molecules in a mole of a substance
G. universal gas constant
D. the ratio of the mass of a substance to its molar mass
E. the ratio of the number of molecules of a substance to the number of molecules in a mole of a substance
7. The amount of substance is equal to the ratio:
A. molecular (atom) mass to molar mass
B. molar mass to Avogadro's constant
B. mass of a substance to relative molecular weight
G. number of molecules (atoms) to Avogadro's constant
D. number of molecules (atoms) to molar mass
E. molecular (atom) mass to Avogadro's constant
The class is divided into groups; using given materials, students prepare a cluster and defend it.
Material for preparation
Properties of gases
Gas (gaseous state) (from the Dutch gas, goes back to the ancient Greek χάος) is one of the four states of aggregation of matter, characterized by very weak bonds between its constituent particles (molecules, atoms or ions), as well as their high mobility. Gas particles move almost freely and chaotically in the intervals between collisions, during which a sharp change in the nature of their movement occurs. The term “gas” can also be defined as a substance whose temperature is equal to or exceeds the critical point; at such a temperature, compression of the gas does not lead to the formation of a liquid. This is the difference between gas and steam. As the pressure increases, saturated steam partially turns into liquid, but gas does not.
The gaseous state of a substance under conditions where the existence of a stable liquid or solid phase of the same substance is possible is usually called vapor.
Like liquids, gases have fluidity and resist deformation. Unlike liquids, gases do not have a fixed volume and do not form a free surface, but tend to fill the entire available volume (for example, a vessel).
The gaseous state is the most common state of matter in the Universe (interstellar matter, nebulae, stars, planetary atmospheres, etc.). By chemical properties gases and their mixtures are very diverse - from low-active inert gases to explosive gas mixtures. The concept of “gas” is sometimes extended not only to aggregates of atoms and molecules, but also to aggregates of other particles - photons, electrons, Brownian particles, as well as plasma.
The most important feature thermal movement gas molecules - this is the disorder (chaotic nature) of movement. Experimental evidence of the continuous nature of molecular motion is diffusion and Brownian motion.
Diffusion is the phenomenon of spontaneous penetration of molecules of one substance into another. As a result of the mutual diffusion of substances, their concentrations gradually level out in all areas of the volume they occupy. It has been established that the rate of the diffusion process depends on the type of substances and temperature.
One of the most interesting phenomena that confirms the chaotic movement of molecules is Brownian motion, which manifests itself in the form of thermal movement of microscopic particles of a substance suspended in a gas. This phenomenon was first observed in 1827 by R. Brown, from whom it received its name. The randomness of the movement of such particles is explained by the random nature of the transfer of impulses from gas molecules to a particle with different sides. Brownian motion turns out to be more noticeable the smaller the particle and the higher the temperature of the system. The dependence on temperature indicates that the speed of chaotic motion of molecules increases with increasing temperature, which is why it is called thermal motion.
Gas as a shock absorber
The shock absorber can be confidently called the most important component of the suspension of any car. Without this small unit, the ride would be simply unbearable due to the continuous vertical rocking of the car body. A car shock absorber plays the role of a kind of damper, dampening vibrations of springs, springs or torsion bars. The mass of the car body is distributed onto the suspension springs in such a way that the latter are constantly compressed by a certain amount depending on the weight of the car and the stiffness of the springs. Thus, each wheel of the car has the ability to move both up and down relative to the body. Due to this, constant contact of each wheel with road surface regardless of whether the wheel hits a bump or a hole. But if there were no shock absorber, then the contact with the road would not be constant due to the vibrations of the springs. Many car enthusiasts are probably familiar with the feeling when the wheels of a car begin to bounce at the slightest bump and even at a speed of 30 km/h they feel a deterioration in control over the car. Such symptoms indicate a failed shock absorber. From all of the above, it can be understood that the shock absorber serves to dampen excessive vibrations of the springs and ensure constant contact of the wheels with the road surface. Types of shock absorbers If you ask any driver what types of shock absorbers he knows, the answer will be something like this: oil, gas-oil and gas. And this is fundamentally wrong, since in absolutely all car shock absorbers there is oil or other liquid (more on this later). Shock absorbers can be more correctly divided into oil and gas. And if we don’t touch on all kinds of pneumatic and adjustable suspensions, then shock absorbers come in single- and double-tube. Twin-pipe oil (hydraulic) shock absorber The hydraulic twin-pipe shock absorber is the simplest, cheapest and, unfortunately, the most unstable. A twin-tube shock absorber consists of the following components: a cylindrical body (reservoir); working cylinder; forward stroke (compression) valve built into the working cylinder; piston; reverse (rebound) valve built into the piston; stock; casing The working cylinder is located in the shock absorber housing, which also serves as a reservoir and is filled with a certain amount of oil. The piston is connected to a rod and is located in the working cylinder. The operating principle of such a shock absorber is very simple. When working in compression, the piston with the rod moves down and displaces oil through the forward valve from the working cylinder into the shock absorber body. In this case, the air located in the upper part of the tank is slightly compressed. When working on rebound, the piston moves in the opposite direction and through the return valve transfers oil from the housing to the working cylinder. The hydraulic shock absorber has a number of serious disadvantages. The main disadvantage is the heating. As is known, the extinction of one energy gives rise to the emergence of another, and in a shock absorber - compensated vibrations of the spring turn into thermal energy and the oil heats up accordingly. Due to the two-pipe design and relatively small volume, the oil heats up quickly, but cools poorly. This problem automatically generates the next one - oil foaming. There is no way to fight this, but experienced car enthusiasts very often try to get rid of aeration by filling a new shock absorber with oil, which is called “to capacity.”
Gas as a working fluid of engines
A working fluid is a conditional irreplaceable material body in heat engineering and thermodynamics that expands when heat is supplied to it and contracts when cooled and performs the work of moving the working body of a heat engine. In theoretical developments, the working fluid usually has the properties of an ideal gas.
In practice, the working fluid of heat engines is the combustion products of hydrocarbon fuels (gasoline, diesel fuel etc.), or water vapor having high thermodynamic parameters (initial: temperature, pressure, speed, etc.)
IN refrigeration machines freons, ammonia, helium, hydrogen, nitrogen are used as the working fluid
THERMAL ENGINE, a machine for converting thermal energy into mechanical work. IN heat engine expansion of the gas occurs, which presses on the piston, causing it to move, or on the blades of the turbine wheel, causing it to rotate. Examples piston engines are steam engines and internal combustion engines (carburetor and diesel). Engine turbines are gas (for example, in aircraft turbojet engines) and steam.
In piston heat engines, hot gas expands in the cylinder, moving the piston and thereby performing mechanical work. To transform the rectilinear reciprocating motion of the piston into rotational movement shaft, a crank mechanism is usually used.
In engines external combustion(for example, in steam engines) the working fluid is heated by burning fuel outside the engine and gas (steam) is supplied to the cylinder under high temperatures and pressure. The gas, expanding and moving the piston, cools, and its pressure drops to close to atmospheric. This exhaust gas is removed from the cylinder, and then a new portion of gas is supplied to it - either after the piston returns to its original position (in single-acting engines - with one-way intake), or with reverse side piston (in engines double acting). In the latter case, the piston returns to its original position under the influence of an expanding new portion of gas, and in single-acting engines the piston is returned to its original position by a flywheel mounted on the crank shaft. In double-acting engines, there are two power strokes for each shaft revolution, while in single-acting engines there are only one; therefore, the first engines are twice as powerful with the same dimensions and speeds.
In internal combustion engines, the hot gas that moves the piston is produced by burning a mixture of fuel and air directly in the cylinder.
To supply fresh portions of the working fluid and release exhaust gas, engines use a valve system. Gas is supplied and released at strictly defined piston positions, which is ensured by a special mechanism that controls the operation of the intake and exhaust valves.
Rarefied gases
The free path length of molecules is inversely proportional to gas pressure. With rarefaction of the gas it naturally increases, reaching, for example, 1 cm at a pressure of 0.009 mm Hg. Art. and several kilometers at high vacuum (high vacuum). Under these conditions, when average length the path becomes much larger than the dimensions of the vessel, collisions between gas molecules occur relatively rarely, and each given molecule flies from one wall of the vessel to the other for the most part without collisions with other molecules. As a result, properties such as viscosity, diffusion, and thermal conductivity, which depend mainly on intermolecular collisions, change significantly. A very strong decrease in the thermal conductivity of gases at high vacuum is practically used in thermos flasks, in industrial and laboratory Dewar vessels. Thermal insulation This is achieved in them mainly by the fact that the vessels are made with double walls and a high vacuum is created in the space between them.
Scottish chemist James Dewar (1842-1923). He prepared a large quantity of liquid oxygen, which he stored in a vessel he invented, called a Dewar vessel. A Dewar flask is a flask with double walls, with air pumped out of the space between them. The thermal conductivity of the rarefied gas between the walls is so low that the temperature of the substance placed in the vessel remains constant for a long time. To further slow down the heat transfer process, the Dewar silvered the walls of the vessel (a household thermos is just a Dewar vessel closed with a stopper.)
deep vacuum
To achieve a deep vacuum, for example about 10-6 mm Hg. Art., use so-called diffusion pumps. There are two main types of diffusion pumps: mercury and oil. They are single-stage and multi-stage, most often two-stage.
Getting a deep vacuum
To achieve a deep vacuum, for example about 10-6 mm Hg. Art., use so-called diffusion pumps. There are two main types of diffusion pumps: mercury and oil. They are single-stage and multi-stage, most often two-stage. The design principle of both types is almost the same.
In Fig. Figure 1 shows a diagram of a glass diffusion mercury pump. It consists of a reservoir 1 with mercury connected to a refrigerator 2. The mercury is brought to a boil by heating gas burner or an electric oven. Mercury vapor rises through tube 3, enters the refrigerator, in which it condenses and returns to the reservoir / through tube 4. The principle of operation of the pump is based on the fact that due to partial condensation of mercury vapor inside the refrigerator near the end of tube 5, the pressure of mercury vapor (or other liquid) turns out to be reduced. Therefore, the gas in tube 6 diffuses into an area with reduced pressure and then is carried away by tube 7 to the forevacuum part of the installation
At a relatively high pressure in the installation, mercury vapor coming out of tube 5, colliding with gas molecules located near the end of this tube, is reflected in all directions. The gas located in Tube 6 diffuses into the counter flow of mercury vapor, which has not yet had time to condense. A diffusion mercury pump should not be used in such cases.
When operating a diffuser pump, it is necessary to carefully monitor the correct cooling of the condensing part. Water should be supplied to the refrigerator before the furnace begins heating under the reservoir with mercury and turned off after the mercury stops boiling. However, the heating of the pump should be turned on only after the fore-vacuum has already been created.
In case of any malfunction of the installation, you should immediately turn off the heating of the mercury pump and do nothing to correct the error or accident until it cools completely. The causes of the accident may be: overheating of the refrigerator as a result of stopping or slowing down the flow of water, breakdown of the refrigerator due to increased water flow through a hot appliance. If the pressure in the installation increases, the boiling of mercury will stop, and its temperature will begin to rise. An accident can also occur when superheated mercury suddenly boils.
To obtain a vacuum of about 10-6 mm Hg. Art. it is necessary to install two single-stage pumps or one two-stage pump in series.
In Fig. Figure 2 shows a two-stage oil high-vacuum diffusion pump with internal electrical heating. Oil should be poured into it no more than 60-70 cm3. It is necessary to ensure that the heating coil is completely covered with a diffusion mineral layer up to 2 mm thick. Excess oil can interfere with normal operation as it causes delayed boiling. After approximately 15 minutes of warming up, the diffusion pump begins to work. If you want to; turn off the pump, first turn off the electric heating, allow the oil to cool to approximately 400C, and only then turn off the cooling and ventilate the pump.
Diffusion oil must be replaced with fresh oil from time to time. The suitability of diffusion oil can be judged by its color: strongly colored oil is unsuitable for work.
Rice. 1. Glass mercury diffusion pump
Rice. 2Glass high vacuum oil two stage diffusion pump.
After removing the oil from the device, the inside of the pump is washed with carbon tetrachloride. Before filling the pump with oil, all solvent residues must be completely removed.
Cluster protection.
Questions for opposing teams.
- Thank you all for your attention! I will give you grades after checking the tests.
Physics lesson report in 10th grade.
This lesson is presented during the study of the section “Fundamentals of Molecular Kinetic Theory.” During the lesson, the age and psychological characteristics of students were taken into account, and information and communication technologies were used.
The purpose of the lesson is : study the properties of gases and their application in technology
Main objectives of the lesson:
educational: to form reflection, the habit of providing assistance and support to each other when performing practical work, conscientious attitude towards the task being performed;
developing: development of speech, memory, attention, interest in the subject, the ability to work with physical instruments, with a textbook, additional literature, the ability to highlight the main thing,
educational: apply knowledge in practice.
The lesson used elements of teaching schoolchildren universal educational activities, an activity-based teaching method was used, which was implemented in the following types activities: educational and educational-research. At all stages of the lesson, students were involved in active mental and practical research activities; children not only had to use their existing knowledge.
The lesson was conducted in a standard form using new technologies.
The stages of the lesson were closely interconnected and alternated different kinds activities. All stages of the lesson were consistent and logically connected. The structure of the lesson corresponds to this type of lesson. The integrity and completeness of the lesson was ensured. Mental actions were based and supported by practical ones. The class was divided into two teams.
One group studied the topic “Properties of gases and applications of gases,” and the second group “gas as a working fluid of an engine. Rarefied gas. Obtaining a deep vacuum."
Each group had to create a cluster on the topic and defend it, as well as explain the topic of their presentation clearly and accessible to the other team.
During the course, I used the following teaching methods: verbal, partially search, visual, problem-dialogical. These teaching methods ensured the exploratory and creative nature of the students’ cognitive activity, and the following visual, literary and technical materials:
The lesson was organized, there was a logical transition from one stage to another, there was clear management of students' academic work, mastery of the class, and adherence to discipline. The intensity of the lesson was optimal taking into account physical and psychological characteristics children.
This presentation is well suited for presenting material in the 10th grade in a specialized physics course. The topic of the lesson reveals the basic concepts: 1. specific heat of vaporization
2. relative air humidity and absolute air humidity
The presentation also discusses the industrial use of liquefied eiders and their production. Instruments for measuring air humidity
Heat of vaporization Liquefaction of gases Air humidity This is the amount of heat required to convert a given mass of liquid into steam of the same temperature Qp, J Q, J
Heat of vaporization Where is the energy supplied to the body spent? To increase its internal energy during the transition from a liquid to a gaseous state, the heat of vaporization depends on the type of liquid, its mass and temperature. This dependence is characterized by the specific heat of vaporization - r, J/kg. The specific heat of vaporization of a given liquid is the ratio of the heat of vaporization of a liquid to its mass =Qп/mr - specific heat of vaporizationm - mass of liquid Qп=rm - energy that is absorbed during vaporization, JQк= -rm - energy that is released during steam condensation, J Liquefaction of gases In 1799, the first gas (ammonia) was converted into liquidEnglish physicist M. Faraday liquefied gases by simultaneously cooling and compressing them. By the second half of the 19th century, only 6 gases remained unconverted: hydrogen, oxygen, nitrogen, nitrous oxide and methane (since there was no technology to obtain low temperatures) Liquefaction plants gas expanders low pressure developed by academician P.L. Kapitsa 1 - compressor, atmospheric air enters there, where it is compressed to a pressure of several tens of atmospheres 2 - heat exchanger, it cools running water hot air and enters the expander cylinder (3) - here it expands, pushes the piston, and cools so much that it condenses into liquid4 - a vessel into which liquefied air enters
Obtaining liquid air
Storage of liquid gases Dewar flask1) Designed like a thermos, has double glass walls, between which there is no air2) The inner wall is shiny - to reduce heating by radiation3) A narrow open neck so that the gas contained in the vessel can gradually evaporate4) When evaporating, the liquefied gas remains cold5) Liquid air remains for several weeks Application liquefied gases
In technology for separating air into its component parts. The method is based on the fact that the various gases that make up air boil at different temperatures2) Liquid oxygen is used as an oxidizer for space rocket engines3) Liquid hydrogen is the fuel in space rockets4) Liquid ammonia is used in refrigerators - huge warehouses where food is stored
Air humidity
Partial pressure of water vapor - the pressure that water vapor would produce if all other gases were absent
absolute air humidity - water vapor density, kg/m3 shows how much water vapor is contained in 1 m3 of air
- absolute humidity, kg/m3 density of saturated water vapor at a given temperature, kg/m3 partial pressure of water vapor, Pa pressure saturated steam, Pa
Relative air humidity Shows how close water vapor is to saturation at a given temperature Dew point - the temperature to which the air must cool for the vapor in it to reach a state of saturation (at a given air humidity and constant pressure) Condensation hygrometer1 - metal box2 - front wall3 – ring4 – heat-insulating gasket5 – rubber bulb
Devices for measuring air humidity Hair hygrometer 1 - metal stand 2 - defatted human hair 3 - nut 4 - arrow 5 - block
Instruments for measuring air humidity Psychrometer
Instruments for measuring air humidity
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