The first law of thermodynamics is the legal version of energy conservation, which is adapted for the thermodynamic system. The energy conservation law states that the total energy of an isolated system is constant; energy can be changed from one form to another, but can not be created or destroyed. The first law is often formulated
It states that changes in internal energy ? U of a closed system is equal to the amount of heat Q supplied to the system, minus the amount of work W done by the system around it. The equivalent statement is that the first immortal motion machine is not possible.
Video First law of thermodynamics
Histori
Investigations about the nature of heat and work and their relationship began with the invention of the first machine used to extract water from the mine. Improvements in such machines thereby increasing their efficiency and power output come earlier than the mechanics that work with such machines but only slowly advance the art. The deeper investigations that put them on the ground of mathematics and physics came later.
The first law of thermodynamics was developed empirically for about half a century. The first complete statements of the law came in 1850 from Rudolf Clausius and from William Rankine; Rankine's statements are considered less clear than Clausius'. The main aspect of the struggle is to deal with the proposed hot calorie theory.
In 1840, Germain Hess declared conservation law for so-called 'heat reactions' to chemical reactions. His law was later recognized as a consequence of the first law of thermodynamics, but Hess's statement does not explicitly relate to the relationship between the exchange of energy with heat and work.
According to Truesdell (1980), Julius Robert von Mayer in 1841 made a statement which meant that "in the process of constant pressure, the heat used to produce a universal expansion can be exchanged for work", but this is not the first general statement of law.
Initial statement: "thermodynamic approach"
The original nineteenth-century statements of the first law of thermodynamics arose in a conceptual framework in which the transfer of energy as heat is taken as a primitive notion, not defined or constructed by the theoretical development of the framework, but presupposed as before and already accepted. The primitive notion of heat is taken empirically, mainly through the calorimetry that is regarded as a subject in itself, before thermodynamics. Together primitive with this idea of ​​heat is the notion of empirical temperatures and thermal equilibrium. This framework also considers primitive as the idea of ​​energy transfer as work. This framework does not consider the concept of energy in general, but regard it as derivative or synthesized from previous ideas about heat and work. By one author, this framework has been called the "thermodynamic" approach.
The first explicit expression of the first law of thermodynamics, by Rudolf Clausius in 1850, refers to the cyclic thermodynamic process.
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- In all cases where work is produced by a heat agent, the amount of heat consumed is proportional to the work performed; and vice versa, by spending the same quantity of work the same heat quantity is generated.
Clausius also states law in other forms, referring to the existence of the system state function, internal energy, and expressed it in terms of differential equations for the addition of thermodynamic processes. This equation can be described as follows:
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- In a thermodynamic process involving a closed system, the internal energy increase is equal to the difference between the heat accumulated by the system and the work done by it.
Because of the definition in terms of addition, the internal energy value of a system is not uniquely defined. This is defined only until the constants are arbitrary integration additives, which can be adjusted to provide zero-reference arbitrary levels. This uniqueness corresponds to the abstract mathematical nature of the internal energy. The internal energy is usually expressed relative to the conventionally selected standard reference state of the system.
The concept of internal energy is considered by Bailyn to be "an enormous interest". The quantity can not be directly measured, but can only be inferred, by distinguishing the actual direct measurement. Bailyn likened it to the atomic energy status, expressed by the energy relations Bohr h? = E n ' ' - E n ' . In each case, unmeasured quantities (internal energy, atomic energy levels) are expressed by considering the difference in measured quantities (adding internal energy, the amount of radiated energy emitted or absorbed).
Conceptual Revision: "mechanical approach"
In 1907, George H. Bryan wrote of a system in which there is no transfer of matter (closed system): "Definition When energy flows from one system or part of the system to a system other than by one system or part of the system. the performance of mechanical work, the energy transferred is called heat . "This definition can be considered as a conceptual revision statement, as follows. This was systematically described in 1909 by Constantin CarathÃÆ'Â © odory, whose attention has been drawn by Max Born. Mostly through Born's influence, the revised conceptual approach to the definition of heat became more favored by many twentieth-century writers. This can be called a "mechanical approach".
Energy can also be transferred from one thermodynamic system to another in relation to the transfer of matter. Born suggests that in general such energy transfer can not be uniquely resolved into work and partially heating. Generally, when there is a transfer of energy associated with the transfer of matter, the work and heat transfer can be differentiated only when they pass the wall physically apart from them for material transfer.
The "mechanical" approach postulates the law of conservation of energy. It also postulates that energy can be transferred from one thermodynamic system to another as an adiabatic work, and that energy can be held as the internal energy of the thermodynamic system. It also postulates that energy can be transferred from one thermodynamic system to another by a non-adiabatic pathway, and is not accompanied by the transfer of matter. Initially, it was "ingenious" (according to Bailyn) refrained from labeling as 'hot' as non-adiabatic, energy transfer without companion. This rests on the primitive notion of wall, especially adiabatic walls and non-adiabatic walls, defined as follows. For a while, just for the purpose of this definition, one can forbid the transfer of energy as a job through an attractive wall. Then the walls of interest fall into two classes, (a) such that the arbitrary systems separated by them remain independent in their respective states which have previously established internal thermodynamic equilibrium; they are defined as adiabatic; and (b) those who do not have such independence; they are defined as non-adiabatic.
This approach obtains the notion of energy transfer as heat, and temperature, as a theoretical development, does not regard it as primitive. He considers calorimetry as a derived theory. It has an early nineteenth-century origin, for example in the work of Helmholtz, but also in the work of many others.
Maps First law of thermodynamics
Statements revised conceptually, according to mechanical approach
The revised statement of the first law postulates that a change in the internal energy of a system because every arbitrary process, which takes the system from the original thermodynamic state given to the final equilibrium thermodynamic state, can be determined through physical existence, for the given states, of the process references that occur purely through adiabatic work stages.
Revised statement later
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- For closed systems, in any interesting arbitration process that takes them from the beginning to the final state of the internal thermodynamic balance, internal energy changes are the same as for adiabatic work process references that connect the two countries. This is so despite the interesting process path, and regardless of whether it is adiabatic or non-adiabatic process. The reference adiabatic work process can be arbitrarily selected from the class of all the processes.
This statement is much less close to the empirical base than the original statement, but is often regarded as conceptually conceptual because it depends only on the concept of adiabatic work and non-adiabatic processes, not on the concept of energy transfer as the heat and the empirical temperatures presupposed by the original assertion. Mostly through the influence of Max Born, it is often considered theoretically preferred because of this conceptual parsimony. Born mainly observed that a revised approach avoids thinking in terms of what he calls the "import engineering" concept of a hot engine.
Basing his thoughts on a mechanical approach, Born in 1921, and again in 1949, proposed to revise the definition of heat. In particular, he refers to the work of Constantin CarathÃÆ'Â © odory, who in 1909 declared the first law without defining the quantity of heat. Born's definition is specific to energy transfer without material transfer, and has been widely followed in textbooks (eg :). Born observed that the transfer of matter between the two systems was accompanied by an internal energy transfer that could not be resolved into a heat and work component. There may be paths to other systems, spatially separated from material transfers, allowing independent and simultaneous heat transfer and work by material transfer. Energy is conserved in such transfers.
Description
Cyclic process
The first law of thermodynamics for a closed system is expressed in two ways by Clausius. One way of referring to the cyclic process and input and output of the system, but does not refer to increases in the internal state of the system. Another way is to refer to additional changes in the internal state of the system, and do not expect the process to be cyclic.
The cycle process is one that can be repeated indefinitely often, restoring the system to its original state. What is interesting for a single cycle of the cycle process is the net work done, and the clean heat taken in (or 'consumed', in Clausius' statement), by the system.
In a cyclic process in which the system works cleanly around it, physically observed is not only necessary that heat be taken into the system, but also, importantly, that some heat leaves the system. The difference is that heat is changed by the cycle into work. In every repetition of the cycle process, the net work performed by the system, measured in a mechanical unit, proportional to the heat consumed, is measured in calorimetric units.
The proportionality constant is universal and independent of the system and in 1845 and 1847 measured by James Joule, which describes it as the mechanical equivalent of heat.
Include convention
In non-cyclic processes, the system's internal energy change equals clean energy added as heat to the system minus the net work done by the system, both of which are measured in mechanical units. Taking ? U as a change in internal energy, someone writes
where Q shows the amount of heat supplied to the system by its environment and W shows the net work performed by the system. The convention of this sign is implicit in Clausius' statement of the law given above. This comes with the study of heat engines that generate useful work with heat consumption.
Often today, however, the authors use IUPAC conventions where the first law is formulated with the work performed on the system with its environment having a positive sign. With the current convention of signing often used to work, the first law for a closed system can be written:
This convention follows physicists such as Max Planck, and considers all clean energy transfers to the system as positive and all clean energy transfers from the system as negative, regardless of any use for the system as a machine or other device.
When the system extends into a fictitious quasistatic process, the work done by the system in the environment is the product, P Ã, V P , and the volume changed, d V , while the work was done on > - P Ã, V . Using the sign convention to work, changes in internal energy of the system are:
where ? Q shows the amount of very small heat supplied to the system from its surroundings.
Work and heat are expressions of the actual physical process of the supply or removal of energy, whereas the internal energy U is a mathematical abstraction that keeps the energy exchange accounts that affect the system. So the hot term for Q means "the amount of energy added or removed by heat conduction or by thermal radiation", rather than referring to an energy form in the system. Likewise, the term work energy for W means "the amount of energy obtained or lost as a result of work". The internal energy is the property of the system whereas the work performed and the heat provided is not. The significant result of this difference is that the given internal energy change is ? U can be achieved by, in principle, many combinations of heat and work.
Wide range of legal statements for closed systems
The law is very important and general and consequently thought of from several points of view. Most statements of legal textbooks state it for closed systems. This is expressed in several ways, sometimes even by the same author.
For the thermodynamics of closed systems, the difference between energy transfer as work and as heat is central and falls within the scope of this article. For open system thermodynamics, such distinctions are beyond the scope of this article, but some limited comments are made at the bottom of this section entitled 'The first law of thermodynamics for open systems'.
There are two main ways of declaring the laws of thermodynamics, physically or mathematically. They must be logically coherent and consistent with each other.
An example of a physical statement is Planck's statement (1897/1903):
- It is impossible, either mechanical, thermal, chemical, or other device, to obtain perpetual motion, ie it is impossible to build machines that will work in cycles and produce continuous work, or kinetic energy, from nothing.
This physical statement is not limited to a closed system or system in a state strictly determined solely for thermodynamic equilibrium; it also means for open systems and for systems with circumstances that are not in thermodynamic equilibrium.
This statement by Crawford, for W , uses the IUPAC sign convention, not from Clausius. Although it does not explicitly say so, this statement refers to a closed system, and to the internal energy U which is determined for the body under thermodynamic equilibrium, which has a well-defined temperature.
The history of the legal statements for closed systems has two main periods, before and after the work of Bryan (1907), of CarathÃÆ'Â © odory (1909), and the approval of CarathÃÆ'Â © odory's work given by Born (1921). Traditional versions of previous law for closed systems today are often considered outmoded.
Thermodynamic presentations CarathÃÆ'Â odory refers to a closed system, which is left to contain several phases connected by the internal walls of various types of impermeability and permeability (explicitly including only heat-able walls). CarathÃÆ'Â © odory's 1909 version of the first law of thermodynamics is expressed in the axiom that refrains from defining or mentioning the temperature or quantity of heat transferred. The axiom states that the internal energy of the phase in equilibrium is the function of the state, that the sum of the internal energy of the phase is the total internal energy of the system, and that the total value of the internal energy of the system is altered by the amount of work done adiabatically above it, considering work as the form of energy. The article considers this statement as an expression of the law of conservation of energy for such a system. This version is now widely accepted as authoritative, but expressed in slightly different ways by different authors.
Statements such as the first law for a closed system affirm the existence of internal energy as a function of state defined in terms of adiabatic work. Thus heat is not defined calorimetrically or due to temperature differences. This is defined as the residual difference between changes in internal energy and work performed on the system, when the work does not take into account all changes in internal energy and the system is not isolated adiabatically.
Karathea's 1909 essay on law in an axiomatic form does not mention heat or temperature, but the explicitly refered equilibrium state is determined by a set of variables that always include "non-deformation variables", such as pressure, which, within reasonable limits, can be correctly interpreted as the empirical temperature, and the walls connecting the system phase are explicitly defined as may be heat proof or permeable only for heat.
According to MÃÆ'¼nster (1970), "The somewhat unsatisfactory aspect of CarathÃÆ'Â © odory's theory is that the consequences of the Second Law should be considered at this point [in the first legal statement], namely that it is not always possible to reach every state 2 from another country via adiabatic process. "For example MÃÆ'¼nster that there is no adiabatic process that can reduce the internal energy of a system at a constant volume. The paper CarathÃÆ'Â © odory confirms that his statements about the first law fit exactly with Joule's experimental setting, which is considered an example of adiabatic work. This does not indicate that Joule's experimental arrangement is done essentially unchangeable work, through friction paddles in liquids, or parts of electric current through resistance within the system, driven by coil motion and inductive heating, or by an external current source. , which can access the system only with the passage of electrons, and is not adiabatic, because electrons are a form of matter, which can not penetrate adiabatic walls. This paper goes on to base its main argument on the possibility of quasi-static adiabatic work, which is essentially recoverable. This paper asserts that it will avoid references to the Carnot cycle, and then proceed to base its argument on the quasi-static adiabatic phase cycle forward and backward, with an isothermal stage of zero magnitude.
Sometimes the concept of internal energy is not made explicit in statements.
Sometimes the existence of internal energy is made explicit but the work is not explicitly mentioned in the first postulated thermodynamic statement. The heat given is then defined as the residual change in internal energy after the work has been taken into account, in the non-adiabatic process.
A respected modern author states the first law of thermodynamics as "Heat is a form of energy", which explicitly does not mention internal energy nor adiabatic work. Heat is defined as the energy transferred by the thermal contact with the reservoir, which has a temperature, and is generally so large that the addition and dissipation of heat does not change its temperature. The text of current students on chemistry defines such heat: " heat is the exchange of heat energy between the system and its surroundings caused by the temperature difference." The author then explains how heat is defined or measured by calorimetry, in terms of heat capacity, specific heat capacity, molar heat capacity, and temperature.
A respected text ignores the exclusion CarathÃÆ'Â odory mentions the heat of the first legal statement for a closed system, and acknowledges the heat calorimetry defined along with internal work and energy. Another respected text defines the heat exchange as determined by the temperature difference, but also mentions that the Born (1921) version is "very thorough". These versions follow the traditional approach which is now considered out of date, exemplified by Planck (1897/1903).
Evidence for the first law of thermodynamics for closed systems
The first law of thermodynamics for closed systems was initially induced from empirically observed evidence, including calorimetric evidence. Currently, however, it is taken to provide a definition of heat through the law of conservation of energy and the definition of work in terms of changes in the external parameters of a system. The original discovery of the law was gradual over a period of perhaps half a century or more, and some early studies in terms of cyclic processes.
The following is an account in case of changes to the state of a closed system through a combined process that is not always cyclic. This account first considers the process in which the first law is easily verified for its simplicity, ie adiabatic processes (where there is no transfer as heat) and dynamic processes (where there is no transfer as work).
Adiabatic process
In the adiabatic process, there is the transfer of energy as work but not as heat. For all the adiabatic processes that take the system from the initial state given to the particular end state, regardless of how the work is done, the total amount of energy that is eventually transferred as work is one and the same, determined only by the initial given and the last state. The work done on a system is defined and measured by changes in mechanical or quasi-mechanical variables external to the system. Physically, adiabatic transfer of energy as work requires the presence of adiabatic cages.
For example, in the Joule experiment, the initial system was a water tank with a paddle wheel inside. If we isolate the tank thermally, and move the rowing wheels with pulleys and weights, we can connect the temperature increase with the mass-derived distance. Next, the system is restored to its original state, isolated again, and the same amount of work is done on the tank using different devices (electric motors, chemical batteries, springs,...). In each case, the number of jobs can be measured independently. Back to the original state is not done by doing adiabatic work on the system. The evidence shows that the final state of water (in particular, its temperature and volume) is the same in every case. It is irrelevant if the work is electrical, mechanical, chemical,... or if done suddenly or slowly, as long as it is done in an adiabatic way, that is, without the transfer of heat into or out of the system.
This kind of evidence shows that to increase the water temperature in the tank, the qualitative type of work done adiabatically is not a problem. No type of qualitative adiabatic work has ever been observed to lower the water temperature in the tank.
Changes from one state to another, such as an increase in temperature and volume, can be done in several stages, for example by the electrical work provided externally on the resistors in the body, and adiabatic extensions that allow the body to work in the environment. It should be pointed out that the timelines of the stages, and their relative magnitudes, do not affect the amount of adiabatic work that needs to be done for state change. According to a respected scholar: "Unfortunately, it seems that such experiments have never been done with caution... Therefore we must recognize that the statements we have stated here, and which are equivalent to the first law of thermodynamics, are not grounded in evidence experimental direct. "Another expression of this view is"... no proper systematic experiment to verify this generalization is directly tried. "
This kind of evidence, the independence of the sequence of stages, combined with the above-mentioned evidence, the independence of the qualitative kind of work, will indicate the existence of important variables of state associated with adiabatic work, but not such a variable of circumstances. represents the quantity preserved. For the latter, evidence of another step, which may be related to the concept of reversibility, as mentioned below.
The important status variables were first identified and represented by Clausius in 1850, but he did not mention it, and he defines it not only from work but also heat transfer in the same process. It was also recognized independently in 1850 by Rankine, which also symbolizes Ã,; and in 1851 by Kelvin who later called it "mechanical energy", and then "intrinsic energy". In 1865, after some hestation, Clausius began calling its country function "energy". In 1882 it was named as an internal energy by Helmholtz. If only adiabatic processes are attractive, and heat can be neglected, the concept of internal energy will almost never appear or be needed. Relevant physics is largely covered by the concept of potential energy, as meant in Helmholtz's 1847 paper on the principle of energy conservation, though it does not relate to the force that can not be explained by a potential, and thus does not fully justify its principle. In addition, the paper was critical of the early Joule's early work. The enormous benefit of the internal energy concept is that it frees thermodynamics from restrictions to cyclic processes, and enables treatment in thermodynamics.
Kecuali di bawah khusus, dan tegasnya, fiksi, kondisi reversibilitas, hanya satu dari proses atau secara empiris layak oleh aplikasi sederhana dari kerja yang disediakan secara eksternal. Alasan untuk ini diberikan sebagai hukum kedua termodinamika dan tidak dipertimbangkan dalam artikel ini.
Such reverse facts can be dealt with in two main ways, from a different point of view:
- Because of Bryan's (1907) work, the most accepted way of dealing with it today, followed by CarathÃÆ'Â © odory, is to rely on the preconceived concept of the quasi-static process, as follows. The actual physical process of energy transfer as work is always at least to some extent irreversible. The irreversibility is often caused by a mechanism known as dissipation, which converts most of the kinetic energy into internal energy. Examples are friction and viscosity. If the process is done slower, less viscous friction or dissipation. In very slow performance limits, the dissipation tends to be zero and then the delimiter, though fictitious and not actual, is reversible back and forth, and is called quasi-static. During the quasi-static process that limits fiction, intensive internal variables of the system are equal to external intensive variables, which reflect the reactive forces given by the surrounding environment. This can be taken to justify the formula
- Another way to fix this is to allow experiments with the heat transfer process to or from the system to be used to justify the formula (1) above. Moreover, it is to some extent with the problem of the lack of direct experimental evidence that the sequence of stages of a process is not a problem in determining the internal energy. This method does not provide theoretical purity in terms of adiabatic work processes, but empirically feasible, and in accordance with the actual experiments performed, such as the above mentioned Joule experiment, and with older traditions.
Such empirical evidence, coupled with such a theory, largely justifies the following statement:
- For all adiabatic processes between two specific conditions of a closed system of each trait, the net work performed is the same regardless of the process detail, and determines the functioning of the state called internal energy, . "
Adynamic Process
The observable complementary aspect of the first law is about heat transfer. Adynamic energy transfer as heat can be measured empirically with changes around the system of interest by calorimetry. This again requires the existence of an adiabatic enclosure of the entire process, the system and its surroundings, although the separating wall between its surroundings and the system is thermally conductive or radiative permeable, not adiabatic. The calorimeter may rely on reasonable measurements of heat, requiring the presence of a thermometer and measurement of temperature changes within the body known to a reasonable heat capacity under certain conditions; or may depend on the latent heat measurement, by measuring the mass of the material that alters the phase, at a temperature determined by the occurrence of phase change under certain conditions in the latent heat body known from the phase change. The calorimeter can be calibrated by adiabatis doing externally determined work on it. The most accurate method is to drain the electrical current from the outside through the resistance inside the calorimeter. Calibration allows comparison of calorimetric measurements of the quantity of heat transferred with the quantity of energy transferred as work. According to one of the textbooks, "The most common tool for measuring is an adiabatic bomb calorimeter . "According to another textbook," Calorimetry is widely used in the laboratory today. "According to one opinion," Most thermodynamic data comes from calorimetry... "In another opinion," The most common method for measuring "heat" is by calorimeter. "
When the system evolves with the transfer of energy as heat, without energy being transferred as work,
Source of the article : Wikipedia
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