The first law of thermodynamics is the law of conservation of energy for thermal processes - establishes the relationship between the amount of heat Q.obtained by the system, change δ U. its internal energy and work A.committed over external bodies:
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According to this law, the energy cannot be created or destroyed; It is transmitted from one system to another and turns from one form to another. The processes that violate the first law of thermodynamics have never been observed.
The first law of thermodynamics does not establish the directions of thermal processes. However, as experience shows, many thermal processes can occur only in one direction. Such processes are called irreversible . For example, with a thermal contact of two bodies with different temperatures, the heat flux is always directed from a warmer body to a colder. There is never a spontaneous heat transfer process from a low temperature body to a body with a higher temperature. Consequently, the process of heat exchange at the final temperature difference is irreversible.
Reversible Processes call the processes of the system transition from one equilibrium state to another, which can be carried out in the opposite direction through the same sequence of intermediate equilibrium states. At the same time, the system itself and the surrounding bodies return to the initial state.
Processes, during which the system remains in a state of equilibrium, is called quasistobatic. All quasistatic processes are reversible. All reversible processes are quasistobatic.
If the working body of the heat machine is brought into contact with the thermal reservoir, the temperature of which in the process of heat exchange remains unchanged, the only reversible process will be an isothermal quasi-static process that flows with an infinitely small difference in the temperature of the working fluid and tank. In the presence of two thermal tanks with different temperatures, the reversible way can be carried out in two isothermal sections. Since the adiabatic process can also be carried out in both directions (adiabatic compression and adiabatic extension), the circular process consisting of two isotherms and two adiabat (Carno cycle) is the only reversible circular process, in which the working body is driven in thermal contact with only two thermal Reservoirs. All other circular processes conducted with two thermal tanks are irreversible.
Irreversible are the processes of transformation of mechanical work into the internal energy energy due to the presence of friction, diffusion processes in gases and liquids, gas stirring processes in the presence of an initial pressure difference, etc., all real processes are irreversible, but they may closely approach reversible processes. Reversible processes are the idealization of real processes.
The first law of thermodynamics cannot distinguish reversible processes from irreversible. It simply requires the thermodynamic process of a certain energy balance and says nothing about whether such a process is possible or not. The direction of spontaneously flowing processes establishes the second law of thermodynamics. It can be formulated as prohibition for certain types of thermodynamic processes.
English physicist W. Kelvin gave in 1851 the following wording of the Second Law:
In the cyclically active heat machine, the process is impossible, the only result of which would be the transformation into the mechanical work of the entire amount of heat obtained from the only thermal tank.
A hypothetical thermal machine in which such a process could occur, called " eternal engine of the second kind " On earthly conditions, such a car could select thermal energy, such as the World Ocean and completely turn it into work. The mass of water in the world ocean is approximately 1021 kg, and with its cooling to one degree, a huge amount of energy would be distinguished (≈ 1024 J), equivalent to the complete combustion of 1017 kg of coal. Energy generated on Earth every year is 104 times less. Therefore, the "Eternal Engine of the second kind" would be no less attractive for humanity than the "first-kind Eternal Engine", prohibited by the first law of thermodynamics.
German physicist R. Clausius gave another wording the Second Law of Thermodynamics :
The process is impossible, the only result of which would be the transmission of energy by heat exchange from a low temperature body to the body with a higher temperature.
It should be noted that both wording of the Second Law of Thermodynamics equivalent. If you allow, for example, that heat can spontaneously (i.e., without the cost of external work), it is possible to conclude to the conclusion about the possibility of creating the "Eternal Motor of the Second Rode". Indeed, let the real heat machine receives the amount of heat from the heater Q.1 and gives the refrigerator the amount of heat Q.2. At the same time work is done A. = Q.1 – |Q.2 |. If the amount of heat | Q.2 | spontaneously passed from the refrigerator to the heater, the final result of the operation of the real heat machine and the "ideal refrigeration machine" would be transformation into the operation of the amount of heat Q.1 – |Q.2 | obtained from the heater without any change in the refrigerator. Thus, the combination of a real heat machine and the "ideal refrigeration machine" is equivalent to the "Eternal Engine of the second kind". Similarly, it is also possible to show that the combination of a "real refrigeration machine" and the "Eternal Engine of the Second Rode" is equivalent to the "ideal refrigeration machine."
The second law of thermodynamics is associated directly with the irreversibility of real thermal processes. The energy of the thermal motion of molecules is qualitatively different from all other types of energy - mechanical, electrical, chemical, etc. The energy of any kind, except for the energy of the thermal motion of molecules, can completely turn into any other type of energy, including in the energy of the thermal motion. The latter may experience the transformation into any other type of energy only partially. Therefore, any physical process in which there is a transformation of any type of energy into the energy of thermal motion of molecules, is an irreversible process, that is, it cannot be fully implemented in the opposite direction.
The general property of all irreversible processes is that they proceed in a thermodynamically non-equilibrium system and as a result of these processes the closed system is approaching the state of thermodynamic equilibrium.
According to this law, the energy cannot be created or destroyed; It is transmitted from one system to another and turns from one form to another. The processes that violate the first law of thermodynamics have never been observed. In fig. 1.5.14 depicts devices prohibited by the first law of thermodynamics.
The first law of thermodynamics does not establish the direction of thermal processes. However, as experience shows, many thermal processes can occur only in one direction. Such processes are called irreversible. For example, with a thermal contact of two bodies with different temperatures, the heat flux is always directed from a warmer body to a colder. There is never a spontaneous heat transfer process from a low temperature body to a body with a higher temperature. Consequently, the process of heat exchange at the final temperature difference is irreversible.
Reversible Processes call the processes of the system transition from one equilibrium state to another, which can be carried out in the opposite direction through the same sequence of intermediate equilibrium states. At the same time, the system itself and the surrounding bodies return to the initial state.
Processes, during which the system remains in a state of equilibrium, is called quasistobatic. All quasistatic processes are reversible. All reversible processes are quasistobatic.
If the working body of the heat machine is brought into contact with the thermal reservoir, the temperature of which in the process of heat exchange remains unchanged, the only reversible process will be an isothermal quasi-static process that flows with an infinitely small difference in the temperature of the working fluid and tank. In the presence of two thermal tanks with different temperatures, the reversible way can be carried out in two isothermal sections. Since the adiabatic process can also be carried out in both directions (adiabatic compression and adiabatic expansion), then a circular process consisting of two isotherms and two adiabat ( carno cycleIt is the only reversible circular process in which the working fluid is driven by heat contact only with two thermal tanks. All other circular processes conducted with two thermal tanks are irreversible.
Irreversible are the processes of transformation of mechanical work into the internal energy energy due to the presence of friction, diffusion processes in gases and liquids, gas stirring processes in the presence of an initial pressure difference, etc., all real processes are irreversible, but they may closely approach reversible processes. Reversible processes are the idealization of real processes.
The first law of thermodynamics cannot distinguish reversible processes from irreversible. It simply requires the thermodynamic process of a certain energy balance and says nothing about whether such a process is possible or not. The direction of spontaneously flowing processes establishes the second law of thermodynamics. It can be formulated as a ban on certain types of thermodynamic processes.
English physicist W. Kelvin gave in 1851 the following wording of the Second Law:
In the cyclically active heat machine, the process is impossible, the only result of which would be the transformation into the mechanical work of the entire amount of heat obtained from the only thermal tank.
A hypothetical thermal machine in which such a process could occur, called the "second-sort perpetual engine". On earthly conditions, such a car could select thermal energy, such as the World Ocean and completely turn it into work. The mass of water in the world ocean is approximately 10 21 kg, and with its cooling to one degree, a huge amount of energy would be distinguished (≈10 24 J), equivalent to complete combustion of 10 17 kg of coal. Energy generated on Earth every year is about 10 4 times less. Therefore, the "Eternal Engine of the second kind" would be no less attractive for humanity than the "first-kind Eternal Engine", prohibited by the first law of thermodynamics.
German physicist R. Clausius gave another wording
Irreversibility of thermal processes
The first law of thermodynamics is the law of conservation of energy in the flow of thermal processes, when the energy of one species turns into another.
The first law of thermodynamics, establishing energy equality in processes flow, the NA gives an indication of what processes proceed in, and why they occur so, and not otherwise.
In the interaction of bodies and systems, the processes occurring have a certain focus. Thus, when the peeling oscillations of the pendulum, its mechanical energy gradually passes into the internal energy of the pendulum and the environment, the opposite process does not occur.
The dissolution of sugar in water, the transfer of heat from the hot bodies to the cold is examples of one-way processes. Examples of irreversible processes are diffusion, thermal conductivity, viscous fluid flow. 11Dine processes got a name irreversible.
C.10. The second law of thermodynamics
The irreversibility of the processes, the direction of possible energy transformations is formulated using the II of the Law of thermodynamics, which is a generalization of human experience and observations of nature phenomena. Let us give its formulation proposed by the German scientist R. Clausius.
The amount of heat cannot be spontaneously transmitted from the body less heated to the body is more heated. Here you should pay attention to the word "spontaneously", i.e. What is happening without the participation of other bodies, without changing their condition.
Our daily experience confirms the loyalty of this law of thermodynamics. So, the room warmly moves from the heated heating battery to air and subjects located in the room, and not vice versa.
In refrigeration machines, heat is closed from the freezer and is transmitted to the environment. However, violation of the II law of thermodynamics does not occur here, since this process does not go spontaneously, but requires the cost of mechanical energy consumed by the refrigerator electric motor, i.e. The process of "exclusion" of heat from the freezer is accompanied by a change in the state of the surrounding bodies.
Irreversibility is characteristic not only for heat transfer process, but also for all spontaneous processes.
Historical reference. Clausis Rudolf Julius Emanuel (1822-1888) - German theoretical physicist, one of the creators of thermodynamics and the kinetic theory of gases. Main works in the field of molecular physics, thermodynamics, theories of steam machines, theoretical mechanics, mathematical physics. Developing ideas S. Carno, formulated the principle of equivalence of warmth and work. In 1850, she proved the relationship between the warmth and mechanical work (the first beginning of the thermodynamics), formulated the second beginning of the thermodynamics: "The heat itself cannot move from a colder body to a warmer."
Karno Nikola Leonard Sadi (1796-1832) - French physicist and engineer. In 1824, published the book "Reflections on the driving force of fire and about machines that can develop this power." In this work, I first proved that useful work can only be obtained if the heat moves from the more heated body to less heated (the second beginning of the thermodynamics). Introduced the concepts of circular and reversible processes, as well as the perfect cycle of thermal machines.
The law of conservation of energy argues that the amount of energy in any processes remains unchanged. But he does not mean anything about what energy transformations are possible.
Law of energy conservation does not forbid processes that are on experience do not occur:
Heating the heated body is colder;
Spontaneous rocking of the pendulum from the state of rest;
Picking sand into stone, etc.
Processes in nature have a certain focus. In the opposite direction, they cannot flow spontaneously. All processes are irreversible (aging and death of organisms).
Irreversible The process can be called such a process inverse which can only be proceeding as one of the links of a more complex process. Spontaneous There are processes that occur without the impact of external bodies, and therefore, without changes in these bodies).
System transition processes from one state to another, which can be carried out in the opposite direction through the same sequence of intermediate equilibrium states, are called reversible. At the same time, the system itself and the surrounding bodies are completely returned to the initial state.
The second law of thermodynamics indicates the direction of possible energy transformations and thereby expresses the irreversibility of processes in nature. It is established by directly generalizing experienced facts.
The wording of R. Clausius: It is impossible to translate heat from a colder system to more hot in the absence of simultaneous changes in both systems or surrounding bodies.
The wording of U. Kelvin: It is impossible to carry out such a periodic process, the only result of which would be obtaining work due to heat taken from one source.
It is impossible to thermal eternal engine of the second kind, i.e. Engine, making mechanical work due to the cooling of any single body.
An explanation of the irreversibility of processes in nature has a statistical (probabilistic) interpretation.
Purely mechanical processes (excluding friction) are reversible, i.e. Invariant (do not change) when replacing T → -t. Each equations of each individual molecule is also invariant with respect to the conversion of time, because Contain only forces depending on the distance. Therefore, the reason for the irreversibility of processes in nature is that macroscopic bodies contain a very large number of particles.
The macroscopic state is characterized by several thermodynamic parameters (pressure, volume, temperature, etc.). The microscopic state is characterized by the reference of the coordinates and velocities (pulses) of all particles that make up the system. One macroscopic state can be implemented with a huge number of microstasses.
Denote: N-complete number of state states, N 1 - the number of microstasses that implement this state, W is the probability of this state.
The greater N 1, the greater the likelihood of this macro, i.e. However, the system will be in this state. The evolution of the system occurs in the direction of unlikely states to more likely. Because Mechanical movement is an ordered movement, and the thermal is chaotic, then the mechanical energy goes into thermal. With heat exchange, a condition in which one body has a higher temperature (the molecules have a higher average kinetic energy), less likely than a condition in which temperatures are equal. Therefore, the heat exchange process occurs in the direction of alignment of temperatures.
Entropy - measure confusion. S - entropy.
where k is the Boltzmann's constant. This equation discloses the statistical meaning of the laws of thermodynamics. The magnitude of entropy in all irreversible processes increases. From this point of view, life is a constant struggle for the reduction of entropy. Entropy is associated with information, because Information leads to order (you will know a lot - soon you will build up).
The law of conservation of energy argues that the amount of energy in any transformations remains unchanged. But he does not mean anything about what energy transformations are possible. Meanwhile, many processes that are fully allowed from the point of view of the law of conservation of energy will never proceed in reality.
Examples of irreversible processes. Heated bodies are gradually cooled by transmitting its energy to colder surrounding bodies. Reverse process of heat transfer from cold
the bodies are not contrary to the law of energy conservation, but such a process has never been observed.
Another example. The oscillations of the pendulum disabled from the equilibrium position are fucked (Fig. 49; 1, 2, 3, 4 - sequential position of the pendulum at maximum deviations from the equilibrium position). Due to the work of friction forces, mechanical energy decreases, and the temperature of the pendulum and the ambient air (and therefore their internal energy) is slightly rising. Energetically admire the reverse process when the amplitude of the oscillations of the pendulum increases due to the cooling of the pendulum itself and the environment. But such a process has never been observed. Mechanical energy spontaneously passes into the inner, but not vice versa. At the same time, an ordered body movement as a whole turns into an unordered thermal movement of the components of its molecules.
General conclusion about the irreversibility of processes in nature. The transition of heat from the hot body to cold and mechanical energy into the inner is examples of the most typical irreversible processes. The number of such examples can be increased almost unlimited. They all say that the processes in nature have a certain direction, in no way reflected in the first law of thermodynamics. All macroscopic processes in nature occur only in one particular direction. In the opposite direction, they cannot spontaneously pass. All processes are irreversible, and the most tragic of them are aging and death of organisms.
Accurate wording of the concept of an irreversible process. To properly understand the being of the irreversibility of the processes, it is necessary to make the following clarification. Irreversible is called such a process that can only leak as one of the links of a more complex process. So, you can again increase the swing of the pendulum oscillations, pushing it with your hand. But this increase occurs not by itself, but it becomes possible as a result of a more complex process, including the movement of the hand.
It is possible in principle to translate heat from the cold body to hot. But for this you need a refrigeration unit that consumes energy.
Cinema "On the contrary". The bright illustration of the irreversibility of phenomena in nature is the viewing of a movie in the opposite direction. For example, jump into the water will look like this. Calm water in the pool begins to spill, legs appear, rapidly moving up and then
and the whole diver. The surface of the water quickly calms down. Gradually, the speed of the diver decreases, and now he is already calmly on the tower. What we see on the screen could actually happen if the processes could be reversed. "The absurdity" of what is happening stems from the fact that we are accustomed to a certain direction of processes and do not doubt the impossibility of their reverse flow. But such a process, as the ascension of the diver on the tower of water, does not contradict either the law of conservation of energy, nor the laws of mechanics, nor any laws, except for the second law of thermodynamics.
The second law of thermodynamics. The second law of thermodynamics indicates the direction of possible energy transformations and thereby expresses the irreversibility of processes in nature. It was established by directly generalizing experienced facts.
There are several formulations of the second law, which, despite the external difference, express, in essence, the same thing and therefore equal.
German scientist R. Clausius formulated this law like this: it is impossible to translate heat from a colder system to more hot in the absence of other simultaneous changes in both systems or in surrounding bodies.
Here there is an experienced fact of a certain direction of heat transfer: the heat itself turns itself from hot bodies to cold. True, in refrigeration plants, heat transfer is carried out from the cold body to a warmer, but this transmission is associated with "other changes in the surrounding bodies": cooling is achieved through work.
The importance of this law is that it can be brought out of the irreversibility of not only the heat transfer process, but also other processes in nature. If the heat in any cases could be spontaneously transmitted from cold bodies to hot, it would make it possible to make other processes. In particular, it would create engines that completely convert internal energy into mechanical.
Entropy. Physical meaning of entropy. Entropy with reversible and irreversible processes in a closed system. Second Beginning thermodynamicsand the transformation of heat into work.
