Let us consider the features of thermodynamic systems. They are usually understood as physical macroscopic forms consisting of a significant number of particles, which do not imply the use of each individual particle to describe the macroscopic characteristics.
There are no restrictions on the nature of the material particles that are the constituent components of such systems. They can be presented in the form of molecules, atoms, ions, electrons, photons.
Peculiarities
Let us analyze the distinctive characteristics of thermodynamic systems. An example is any object that can be observed without the use of telescopes or microscopes. To give a full description of such a system, macroscopic details are selected, thanks to which it is possible to determine the volume, pressure, temperature, electrical polarization, magnetic induction, chemical composition, and mass of components.
For any thermodynamic systems, there are conditional or real boundaries that separate them from the environment. Instead, the concept of a thermostat is often used, characterized by such a high heat capacity that in the case of heat exchange with the analyzed system, the temperature indicator remains unchanged.
System classification
Let's consider what the classification of thermodynamic systems is. Depending on the nature of its interaction with the environment, it is customary to distinguish:
- isolated species that do not exchange either matter or energy with the external environment;
- adiabatically isolated, not exchanging matter with the external environment, but entering into an exchange of work or energy;
- In closed thermodynamic systems there is no exchange of matter, only changes in the energy value are allowed;
- open systems are characterized by complete transfer of energy and matter;
- partially open ones may have semi-permeable partitions, therefore not fully participating in material exchange.
Depending on the description, the parameters of a thermodynamic system can be divided into complex and simple options.
Features of simple systems
Simple systems are called equilibrium states, the physical state of which can be determined by specific volume, temperature, and pressure. Examples of thermodynamic systems of this type are isotropic bodies that have equal characteristics in different directions and points. Thus, liquids, gaseous substances, solids that are in a state of thermodynamic equilibrium are not exposed to electromagnetic and gravitational forces, surface tension, and chemical transformations. The analysis of simple bodies is recognized in thermodynamics as important and relevant from a practical and theoretical point of view.
The internal energy of a thermodynamic system of this type is connected with the surrounding world. When describing, the number of particles and the mass of the substance of each individual component are used.
Complex systems
Complex thermodynamic systems include thermodynamic systems that do not fall under simple types. For example, they are magnets, dielectrics, solid elastic bodies, superconductors, phase interfaces, thermal radiation, and electrochemical systems. As parameters used to describe them, we note the elasticity of the spring or rod, the phase interface, and thermal radiation.
A physical system is a set in which there is no chemical interaction between substances within the limits of temperature and pressure selected for research. And chemical systems are those options that involve interaction between its individual components.
The internal energy of a thermodynamic system depends on its isolation from the outside world. For example, as a variant of an adiabatic shell, one can imagine a Dewar flask. Homogeneous character is manifested in a system in which all components have similar properties. Examples of them are gaseous, solid, and liquid solutions. A typical example of a gaseous homogeneous phase is the Earth's atmosphere.
Features of thermodynamics
This section of science deals with the study of the basic patterns of processes that are associated with the release and absorption of energy. Chemical thermodynamics involves the study of mutual transformations of the constituent parts of a system, the establishment of patterns of transition of one type of energy to another under given conditions (pressure, temperature, volume).
The system that is the object of thermodynamic research can be represented in the form of any natural object, including a large number of molecules that are separated by an interface with other real objects. The state of a system is understood as the totality of its properties, which make it possible to determine it from the standpoint of thermodynamics.
Conclusion
In any system, a transition from one type of energy to another is observed, and thermodynamic equilibrium is established. The section of physics that deals with the detailed study of transformations, changes, and conservation of energy is of particular importance. For example, in chemical kinetics it is possible not only to describe the state of a system, but also to calculate the conditions that contribute to its displacement in the desired direction.
Hess's law, which relates the enthalpy and entropy of the transformation under consideration, makes it possible to identify the possibility of a spontaneous reaction occurring and to calculate the amount of heat released (absorbed) by a thermodynamic system.
Thermochemistry, based on the fundamentals of thermodynamics, is of practical importance. Thanks to this section of chemistry, preliminary calculations of fuel efficiency and the feasibility of introducing certain technologies into actual production are carried out in production. Information obtained from thermodynamics makes it possible to apply the phenomena of elasticity, thermoelectricity, viscosity, and magnetization for the industrial production of various materials.
THERMODYNAMIC SYSTEM
THERMODYNAMIC SYSTEM
A set of macroscopic bodies that can interact with each other and with other bodies (external environment) - exchange energy and substances with them. T.s. consists of such a large number of structural particles (atoms, molecules) that its state can be characterized macroscopically. parameters: density, pressure, concentration of substances forming T.s., etc.
THERMODYNAMIC EQUILIBRIUM), if the parameters of the system do not change over time and there is no substance in the system. stationary flows (heat, water, etc.). For equilibrium T.s. the concept of temperature is introduced as a parameter that has the same value for all macroscopic objects. parts of the system. The number of independent parameters of a state is equal to the number of degrees of freedom of the T.S.; the remaining parameters can be expressed in terms of independent parameters using the equation of state. Saints of equilibrium T.s. studies equilibrium processes (thermostatics); holy of nonequilibrium systems - .
Thermodynamics considers: closed thermodynamic systems that do not exchange substances with other systems, but that exchange substances and energy with other systems; adiabatic T. systems, in which it is absent with other systems; isolated systems that do not exchange energy or substances with other systems. If the system is not isolated, then its state may change; change in the state of T. s. called thermodynamic process. T.s. can be physically homogeneous (homogeneous system) and heterogeneous (heterogeneous system), consisting of several. homogeneous parts with different physical Holy you. As a result of phase and chemical transformations (see PHASE TRANSITION) homogeneous T. s. may become heterogeneous and vice versa.
Physical encyclopedic dictionary. - M.: Soviet Encyclopedia. . 1983 .
THERMODYNAMIC SYSTEM
A set of macroscopic bodies that can interact with each other and with other bodies (external environment) - exchange energy and matter with them. T.s. consists of such a large number of structural particles (atoms, molecules) that its state can be characterized macroscopically. parameters: density, pressure, concentration of substances forming solids, etc.
T.s. is in equilibrium (cf. Thermodynamic equilibrium), if the parameters of the system do not change over time and there is no material in the system. stationary flows (heat, matter, etc.). For equilibrium T.s. the concept is introduced temperature How state parameter, having the same meaning for all macroscopic. parts of the system. The number of independent state parameters is equal to the number degrees of freedom T.S., the remaining parameters can be expressed in terms of independent ones using equations of state. Properties of equilibrium T.s. studies thermodynamics equilibrium processes (thermostatics), properties of non-equilibrium systems - thermodynamics of nonequilibrium processes.
Thermodynamics considers: closed thermodynamic systems that do not exchange matter with other systems; open systems, exchanging matter and energy with other systems; a d i a b a t n e T.s., in which there is no heat exchange with other systems; isolated T. homogeneous system) and heterogeneous ( heterogeneous system), consisting of several homogeneous parts with different physical properties. properties. As a result of phase and chemical transformations (see Phase transition) homogeneous T. s. may become heterogeneous and vice versa.
Lit.: Epshtein P.S., Course of Thermodynamics, trans. from English, M.-L., 1948; Leontovich M.A., Introduction to Thermodynamics, 2nd ed., M.-L., 1951; Samoilovich A, G., Thermodynamics and, 2nd ed., M., 1955.
Physical encyclopedia. In 5 volumes. - M.: Soviet Encyclopedia. Editor-in-chief A. M. Prokhorov. 1988 .
See what "THERMODYNAMIC SYSTEM" is in other dictionaries:
A macroscopic body isolated from the environment using partitions or shells (they can also be mental, conditional) and characterized by macroscopic parameters: volume, temperature, pressure, etc. For this... ... Big Encyclopedic Dictionary
thermodynamic system- thermodynamic system; system A set of bodies that can energetically interact with each other and with other bodies and exchange matter with them... Polytechnic terminological explanatory dictionary
THERMODYNAMIC SYSTEM- a set of physical bodies that can exchange energy and matter with each other and with other bodies (external environment). T.s. is any system consisting of a very large number of molecules, atoms, electrons and other particles having many... ... Big Polytechnic Encyclopedia
thermodynamic system- A body (a set of bodies) capable of exchanging energy and (or) matter with other bodies (with each other). [Collection of recommended terms. Issue 103. Thermodynamics. Academy of Sciences of the USSR. Committee of Scientific and Technical Terminology. 1984... Technical Translator's Guide
thermodynamic system- - an arbitrarily selected part of space containing one or more substances and separated from the external environment by a real or conditional shell. General chemistry: textbook / A. V. Zholnin ... Chemical terms
thermodynamic system- a macroscopic body, separated from the environment by real or imaginary boundaries, which can be characterized by thermodynamic parameters: volume, temperature, pressure, etc. There are isolated,... ... Encyclopedic Dictionary of Metallurgy
A macroscopic body isolated from the environment using partitions or shells (they can also be mental, conditional), which can be characterized by macroscopic parameters: volume, temperature, pressure, etc. For... ... encyclopedic Dictionary
Thermodynamics ... Wikipedia
thermodynamic system- termodinaminė sistema statusas T sritis chemija apibrėžtis Kūnas (kūnų visuma), kurį nuo aplinkos skiria reali ar įsivaizduojama riba. atitikmenys: engl. thermodynamic system rus. thermodynamic system... Chemijos terminų aiškinamasis žodynas
thermodynamic system- termodinaminė sistema statusas T sritis fizika atitikmenys: engl. thermodynamic system vok. thermodynamisches System, n rus. thermodynamic system, f pranc. système thermodynamique, m … Fizikos terminų žodynas
Introduction. The subject of thermal engineering. Basic concepts and definitions. Thermodynamic system. State parameters. Temperature. Pressure. Specific volume. Equation of state. Van der Waals equation .
Ratio between units:
1 bar = 10 5 Pa
1 kg/cm 2 (atmosphere) = 9.8067 10 4 Pa
1mmHg st (millimeter of mercury) = 133 Pa
1 mm water. Art. (millimeter of water column) = 9.8067 Pa
Density - the ratio of the mass of a substance to the volume occupied by that substance.
Specific volume - the reciprocal of density, i.e. ratio of the volume occupied by a substance to its mass.
Definition: If in a thermodynamic system at least one of the parameters of any body included in the system changes, then the system experiences thermodynamic process .
Basic thermodynamic parameters of the state P, V, T homogeneous bodies depend on one another and are mutually related by the equation of state:
F (P, V, T)
For an ideal gas, the equation of state is written as:
P- pressure
v- specific volume
T- temperature
R- gas constant (each gas has its own value)
If the equation of state is known, then to determine the state of the simplest systems it is enough to know two independent variables out of 3
P = f1 (v, t); v = f2 (P, T); T = f3(v, P).
Thermodynamic processes are often depicted on state graphs, where state parameters are plotted along the axes. The points on the plane of such a graph correspond to a certain state of the system, the lines on the graph correspond to thermodynamic processes that transfer the system from one state to another.
Let us consider a thermodynamic system consisting of one body of some gas in a vessel with a piston, and the vessel and piston in this case are the external environment.
Let, for example, the gas is heated in a vessel, two cases are possible:
1) If the piston is fixed and the volume does not change, then the pressure in the vessel will increase. This process is called isochoric(v = const), running at constant volume;
Rice. 1.1. Isochoric processes in P-T coordinates: v 1 >v 2 >v 3
2) If the piston is free, then the heated gas will expand; at constant pressure, this process is called isobaric (P= const), running at constant pressure.
Rice. 1.2 Isobaric processes in v - T coordinates: P 1 >P 2 >P 3
If, by moving the piston, you change the volume of gas in the vessel, then the temperature of the gas will also change, however, by cooling the vessel during gas compression and heating during expansion, you can achieve that the temperature will be constant with changes in volume and pressure, this process is called isothermal (T= const).
Rice. 1.3 Isothermal processes in P-v coordinates: T 1 >T 2 >T 3
A process in which there is no heat exchange between the system and the environment is called adiabatic, while the amount of heat in the system remains constant ( Q= const). In real life, adiabatic processes do not exist since it is not possible to completely isolate the system from the environment. However, processes often occur in which the heat exchange with the environment is very small, for example, rapid compression of gas in a vessel by a piston, when heat does not have time to be removed due to heating of the piston and vessel.
Rice. 1.4 Approximate graph of an adiabatic process in P-v coordinates
Definition: Circular process (Cycle) - is a set of processes that return the system to its original state. There can be any number of separate processes in a loop.
The concept of a circular process is key for us in thermodynamics, since the operation of a nuclear power plant is based on a steam-water cycle, in other words, we can consider the evaporation of water in the core, rotation of the turbine rotor by steam, condensation of steam and the flow of water into the core as a kind of closed thermodynamic process or cycle.
Definition: Work body - a certain amount of a substance that, participating in the thermodynamic cycle, performs useful work. The working fluid in the RBMK reactor plant is water, which, after evaporating in the core in the form of steam, does work in the turbine, rotating the rotor.
Definition: The transfer of energy in a thermodynamic process from one body to another, associated with a change in the volume of the working fluid, with its movement in external space or with a change in its position is called process work .
Thermodynamic system
Technical thermodynamics (t/d) examines the patterns of mutual conversion of heat into work. It establishes the relationship between thermal, mechanical and chemical processes that occur in heat and refrigeration machines, studies the processes occurring in gases and vapors, as well as the properties of these bodies under various physical conditions.
Thermodynamics is based on two basic laws (principles) of thermodynamics:
First law of thermodynamics- the law of transformation and conservation of energy;
II law of thermodynamics- establishes the conditions for the occurrence and direction of macroscopic processes in systems consisting of a large number of particles.
Technical technology, applying the basic laws to the processes of converting heat into mechanical work and vice versa, makes it possible to develop theories of heat engines, study the processes occurring in them, etc.
The object of the study is thermodynamic system, which can be a group of bodies, a body or a part of a body. What is outside the system is called environment. A T/D system is a collection of macroscopic bodies that exchange energy with each other and the environment. For example: a t/d system is a gas located in a cylinder with a piston, and the environment is a cylinder, a piston, air, and room walls.
Isolated system - t/d system does not interact with the environment.
Adiabatic (thermal insulated) system - the system has an adiabatic shell, which excludes heat exchange (heat exchange) with the environment.
Homogeneous system - a system that has the same composition and physical properties in all its parts.
Homogeneous system - a homogeneous system in composition and physical structure, inside which there are no interfaces (ice, water, gases).
Heterogeneous system
- a system consisting of several homogeneous parts (phases) with different physical properties, separated from one another by visible interfaces (ice and water, water and steam).
In heat engines (engines), mechanical work is performed with the help of working fluids - gas, steam.
The properties of each system are characterized by a number of quantities, which are usually called thermodynamic parameters. Let's consider some of them, using the molecular kinetic concepts known from the physics course about an ideal gas as a collection of molecules that have vanishingly small sizes, are in random thermal motion and interact with each other only through collisions.
The pressure is caused by the interaction of the molecules of the working fluid with the surface and is numerically equal to the force acting per unit area of the body surface normal to the latter. In accordance with molecular kinetic theory, gas pressure is determined by the relation
Where n— number of molecules per unit volume;
T— mass of the molecule; from 2- root mean square speed of translational motion of molecules.
In the International System of Units (SI), pressure is expressed in pascals (1 Pa = 1 N/m2). Since this unit is small, it is more convenient to use 1 kPa = 1000 Pa and 1 MPa = 10 6 Pa.
Pressure is measured using pressure gauges, barometers and vacuum gauges.
Liquid and spring pressure gauges measure gauge pressure, which is the difference between total or absolute pressure R measured medium and atmospheric pressure
p atm, i.e.
Instruments for measuring pressures below atmospheric are called vacuum meters; their readings give the vacuum (or vacuum) value:
i.e. excess atmospheric pressure over absolute pressure.
It should be noted that the state parameter is absolute pressure. This is what is included in thermodynamic equations.
Temperatureis called a physical quantity, characterizing the degree of heating of the body. The concept of temperature follows from the following statement: if two systems are in thermal contact, then if their temperatures are unequal, they will exchange heat with each other, but if their temperatures are equal, then there will be no heat exchange.
From the point of view of molecular kinetic concepts, temperature is a measure of the intensity of thermal motion of molecules. Its numerical value is related to the average kinetic energy of the molecules of the substance:
Where k- Boltzmann constant equal to 1.380662.10? 23 J/K. The temperature T defined in this way is called absolute.
The SI unit of temperature is the kelvin (K); in practice, degrees Celsius (°C) are widely used. The relationship between absolute T and centigrade I temperatures has the form
In industrial and laboratory conditions, temperature is measured using liquid thermometers, pyrometers, thermocouples and other instruments.
Specific volume v— is the volume per unit mass of a substance. If a homogeneous body of mass M takes up volume v, then by definition
v= V/M.
In the SI system, the unit of specific volume is 1 m 3 /kg. There is an obvious relationship between the specific volume of a substance and its density:
To compare quantities characterizing systems in identical states, the concept of “normal physical conditions” is introduced:
p= 760 mmHg = 101.325 kPa; T= 273,15 K.
Different branches of technology and different countries introduce their own “normal conditions”, somewhat different from those given, for example, “technical” ( p= 735.6 mm Hg. = 98 kPa, t= 15?C) or normal conditions for assessing compressor performance ( p= 101.325 kPa, t= 20? C), etc.
If all thermodynamic parameters are constant in time and the same at all points of the system, then this state of the system is called equi-spring.
If there are differences in temperature, pressure and other parameters between different points in the system, then it is nonequilibrium. In such a system, under the influence of parameter gradients, flows of heat, substances and others arise, striving to return it to a state of equilibrium. Experience shows that An isolated system always reaches a state of equilibrium over time and can never spontaneously leave it. In classical thermodynamics, only equilibrium systems are considered.
Equation of state. For an equilibrium thermodynamic system, there is a functional relationship between the state parameters, which is called equation of state. Experience shows that the specific volume, temperature and pressure of the simplest systems, which are gases, vapors or liquids, are related thermal equation state of view:
The equation of state can be given another form:
These equations show that of the three main parameters that determine the state of the system, any two are independent.
To solve problems using thermodynamic methods, it is absolutely necessary to know the equation of state. However, it cannot be obtained within the framework of thermodynamics and must be found either experimentally or by methods of statistical physics. The specific form of the equation of state depends on the individual properties of the substance.
Thermodynamic system- this is a part of the material world, separated from the environment by real or imaginary boundaries and is the object of study of thermodynamics. The environment is much larger in volume, and therefore changes in it are insignificant compared to changes in the state of the system. Unlike mechanical systems, which consist of one or several bodies, a thermodynamic system contains a very large number of particles, which gives rise to completely new properties and requires different approaches to describing the state and behavior of such systems. The thermodynamic system is macroscopic object.
Classification of thermodynamic systems
1. By composition
A thermodynamic system consists of components. Component - is a substance that can be isolated from the system and exist outside it, i.e. components are independent substances.
Single-component.
Two-component, or binary.
Three-component - triple.
Multicomponent.
2. By phase composition– homogeneous and heterogeneous
Homogeneous systems have the same macroscopic properties at any point in the system, primarily temperature, pressure, concentration, as well as many others, for example, refractive index, dielectric constant, crystal structure, etc. Homogeneous systems consist of a single phase.
Phase is a homogeneous part of the system, separated from other phases by an interface and characterized by its own equation of state. Phase and state of aggregation are overlapping, but not identical concepts. There are only 4 states of aggregation; there can be many more phases.
Heterogeneous systems consist of at least two phases.
3. By type of relationship with the environment(according to the possibilities of exchange with the environment).
Isolated the system does not exchange either energy or matter with the environment. This is an idealized system, which, in principle, cannot be studied experimentally.
Closed the system can exchange energy with the environment, but does not exchange matter.
Open the system exchanges both energy and matter
TDS condition
TDS condition is the totality of all its measurable macroscopic properties, which therefore have a quantitative expression. The macroscopic nature of the properties means that they can only be attributed to the system as a whole, and not to the individual particles that make up the close binary structure (T, p, V, c, U, n k). Quantitative characteristics of the state are interconnected. Therefore, there is a minimum set of system characteristics called parameters , the specification of which allows us to fully describe the properties of the system. The number of these parameters depends on the type of system. In the simplest case, for a closed homogeneous gas system in a state of equilibrium, it is enough to set only 2 parameters. For an open system, in addition to these 2 characteristics of the system, it is necessary to specify the number of moles of each component.
Thermodynamic variables are divided into:
- external, which are determined by the properties and coordinates of the system in the environment and depend on the contacts of the system with the environment, for example, the mass and number of components, electric field strength, the number of such variables is limited;
- internal, which characterize the properties of the system, for example, density, internal energy, the number of such parameters is unlimited;
- extensive, which are directly proportional to the mass of the system or the number of particles, for example, volume, energy, entropy, heat capacity;
-intense, which do not depend on the mass of the system, for example, temperature, pressure.
TDS parameters are related to each other by a relationship called equation state systems. General view of it f(p,V , T)= 0. One of the most important tasks of FH is to find the equation of state of any system. So far, the exact equation of state is known only for ideal gases (Clapeyron-Mendeleev equation).
pV = nRT, ( 1.1)
Where R– universal gas constant = 8.314 J/(mol.K).
[p] = Pa, 1 atm = 1.013*10 5 Pa = 760 mm Hg,
[V] = m3, [T] = K, [n] = mol, N = 6.02*1023 mol-1. Real gases are only approximately described by this equation, and the higher the pressure and lower the temperature, the greater the deviation from this equation of state.
Distinguish equilibrium And nonequilibrium state of the TDS.
Classical thermodynamics is usually limited to the consideration of equilibrium states of close binary systems. Equilibrium - this is the state to which the TDS spontaneously comes, and in which it can exist indefinitely in the absence of external influences. To determine the equilibrium state, a smaller number of parameters is always required than for nonequilibrium systems.
The equilibrium state is divided into:
- sustainable(stable) state in which any infinitesimal impact causes only an infinitesimal change in state, and when this impact is eliminated, the system returns to its original state;
- metastable a condition in which some final influences cause final changes in state that do not disappear when these influences are eliminated.
A change in the state of a close-body system associated with a change in at least one of its thermodynamic variables is called thermodynamic process. A peculiarity of the description of thermodynamic processes is that they are characterized not by the rates of change in properties, but by the magnitude of the changes. A process in thermodynamics is a sequence of states of a system leading from the initial set of thermodynamic parameters to the final one. The following thermodynamic processes are distinguished:
- spontaneous, for the implementation of which you do not need to expend energy;
- non-spontaneous, occurring only when energy is expended;
- irreversible(or nonequilibrium) - when as a result of the process it is impossible to return the system to its original state.
-reversible - these are idealized processes that pass forward and backward through the same intermediate states, and after completion of the cycle no changes are observed either in the system or in the environment.
Status functions– these are characteristics of the system that depend only on the parameters of the state, but do not depend on the method of achieving it.
State functions are characterized by the following properties:
Infinitesimal change of function f is a total differential df;
The change in function upon transition from state 1 to state 2 is determined only by these states ∫ df = f 2 – f 1
As a result of any cyclic process, the state function does not change, i.e. equal to zero.
Heat and work– methods of energy exchange between the RDS and the environment. Heat and work are characteristics of a process; they are not functions of state.
Job- a form of energy exchange at the macroscopic level when directed movement of an object occurs. Work is considered positive if it is performed by the system against external forces.
Heat– a form of energy exchange at the microscopic level, i.e. in the form of a change in the chaotic movement of molecules. It is generally accepted that the heat received by the system and the work done on it are positive, i.e. the “egoistic principle” operates .
The most commonly used units of energy and work, particularly in thermodynamics, are the SI joule (J) and the non-systemic unit calorie (1 cal = 4.18 J).
Depending on the nature of the object, different types of work are distinguished:
1. Mechanical - body movement
dA fur = - F ex dl.(2.1)
Work is the scalar product of 2 vectors of force and displacement, i.e.
|dA fur | = F dl cosα. If the direction of the external force is opposite to the movement performed by the internal forces, then cosα < 0.
2. Extension operation (gas expansion is most often considered)
dA = - p dV (1.7)
However, it must be borne in mind that this expression is valid only for a reversible process.
3. Electric – movement of electric charges
dA el = -jdq,(2.2)
Where j- electric potential.
4. Superficial – change in surface area,
dA surface = -sdS,(2.3)
Where s- surface tension.
5. General expression for work
dA = - Ydx,(2.4)
Y– generalized force, dx- generalized coordinate, so the work can be considered as the product of an intensive factor and a change in an extensive factor.
6. All types of work, except expansion work, are called useful work (dA’). dA = рdV + dА’ (2.5)
7. By analogy, we can introduce the concept chemical work when moving directionally k-th chemical substance, n k– extensive property, while intensive parameter m k called chemical potential k-th substance
dA chemical = -Sm k dn k. (2.6)
Definition 1
A thermodynamic system is a collection and constancy of macroscopic physical bodies that always interact with each other and with other elements, exchanging energy with them.
In thermodynamics, they usually understand a system as a macroscopic physical form that consists of a huge number of particles that do not imply the use of macroscopic indicators to describe each individual element. There are no certain restrictions in the nature of material bodies that are constituent components of such concepts. They can be represented as atoms, molecules, electrons, ions and photons
Thermodynamic systems come in three main types:
- isolated - there is no exchange with matter or energy with the environment;
- closed - the body is not interconnected with the environment;
- open - there is both energy and mass exchange with external space.
The energy of any thermodynamic system can be divided into energy that depends on the position and movement of the system, as well as energy that is determined by the movement and interaction of microparticles that form the concept. The second part is called in physics the internal energy of the system.
Features of thermodynamic systems
Figure 1. Types of thermodynamic systems. Author24 - online exchange of student work
Note 1
The distinctive characteristics of systems in thermodynamics can be any object observed without the use of microscopes and telescopes.
To provide a complete description of such a concept, it is necessary to select macroscopic details through which it is possible to accurately determine pressure, volume, temperature, magnetic induction, electrical polarization, chemical composition, and mass of moving components.
For any thermodynamic systems there are conditional or real limits that separate them from the environment. Instead, they often consider the concept of a thermostat, which is characterized by such a high heat capacity that in the case of heat exchange with the analyzed concept, the temperature parameter remains unchanged.
Depending on the general nature of the interaction of a thermodynamic system with the environment, it is customary to distinguish:
- isolated species that do not exchange either matter or energy with the external environment;
- adiabatically isolated - systems that do not exchange matter with the external environment, but enter into an exchange of energy;
- closed systems - those that do not exchange with matter; only a slight change in the value of internal energy is allowed;
- open systems - those that are characterized by the complete transfer of energy and matter;
- partially open - have semi-permeable partitions, therefore they do not fully participate in material exchange.
Depending on the formulation, the meaning of the thermodynamic concept can be divided into simple and complex options.
Internal energy of systems in thermodynamics
Figure 2. Internal energy of a thermodynamic system. Author24 - online exchange of student work
Note 2
The main thermodynamic indicators, which directly depend on the mass of the system, include internal energy.
It includes kinetic energy due to the movement of elementary particles of matter, as well as potential energy that appears during the interaction of molecules with each other. This parameter is always unambiguous. That is, the meaning and realization of internal energy are constant whenever the concept is in the desired state, regardless of the method by which this position was achieved.
In systems whose chemical composition remains unchanged during energy transformations, when determining internal energy it is important to take into account only the energy of thermal motion of material particles.
A good example of such a system in thermodynamics is an ideal gas. Free energy is a certain amount of work that a physical body could do in an isothermal reversible process, or free energy represents the maximum possible functional that a concept can perform, possessing a significant supply of internal energy. The internal energy of the system is equal to the sum of the bound and free tension.
Definition 2
Bound energy is that part of internal energy that is not capable of independently turning into work - this is a devalued element of internal energy.
At the same temperature, this parameter increases with increasing entropy. Thus, the entropy of a thermodynamic system is a measure of the provision of its initial energy. In thermodynamics there is another definition - energy loss in a stable isolated system
A reversible process is a thermodynamic process that can proceed rapidly in both the reverse and forward directions, passing through the same intermediate positions, with the concept eventually returning to its original state without the expenditure of internal energy, and no macroscopic changes remain in the surrounding space.
Reversible processes produce maximum work. In practice, it is impossible to obtain the best results from the system. This gives a theoretical significance to reversible phenomena, which proceeds infinitely slowly and can only be approached at short distances.
Definition 3
In science, irreversible is a process that cannot be carried out in the opposite direction through the same intermediate states.
All real phenomena are irreversible in any case. Examples of such effects are thermal diffusion, diffusion, viscous flow, and thermal conduction. The transition of kinetic and internal energy of macroscopic motion through constant friction into heat, that is, into the system itself, is an irreversible process.
System State Variables
The state of any thermodynamic system can be determined by the current combination of its characteristics or properties. All new variables that are fully determined only at a certain point in time and do not depend on how exactly the concept came to this position are called thermodynamic parameters of state or basic functions of space.
In thermodynamics, a system is considered stationary if the variable values remain stable and do not change over time. One of the options for a stationary state is thermodynamic equilibrium. Any, even the most insignificant, change in the concept is already a physical process, so it can contain from one to several variable state indicators. The sequence in which the states of a system systematically transform into each other is called the “process path.”
Unfortunately, confusion with terms and detailed descriptions still exists, because the same variable in thermodynamics can be either independent or the result of the addition of several functions of the system at once. Therefore, terms such as “state parameter”, “state function”, “state variable” can sometimes be considered as synonyms.