First Law of Thermodynamics: Thermodynamic Work, Adiabatic Work, Internal Energy, Concept of Heat, Heat Capacity, Specific Heat, Enthalpy. | Study Physics by Adrian Bathrooms Couso
The thermodynamic work is defined as the energy transferred between a system and its surroundings when the two a force is exerted. Numerically, the infinitesimal work "d~W" that makes a force "F" to the point of application suffer displacement "dr" is given by the expression: = F dr d~W.
If a system jointly or exerts a force on the surrounding environment and has a displacement of the point of application of the former, the work done by or on the system is called external work. If the work is done by one party over another is called inside job. In thermodynamics the internal work has no interest and only care about the external work, that is an interaction between a system and its outside environment.
In interactions experienced by thermodynamic sitemas, they can receive or give energy, because if the system receives is because the is giving the middle, or vice versa, it is necessary to establish a criterion of signs that allow us to interpret the results to be obtained. Thus, the IUPAC (acronym for the International Union of Pure and Applied Chemistry) recommended in 1970 that the same criteria be considered in Mechanics. This means that if the force is performed by the external environment on the system and displacement have the same sense, it is the system that increases your energy and, therefore, is said to have done work on the system and considered positive work. Conversely, if the work is done by the system on the exterior medium and the displacement is the same direction, the energy of the system decreases and it is considered negative working.
The thermodynamic definition of work is broader than the definition rechargable fan in mechanical terms indicated by the above equation. For example, the flow of electric current through the boundary of a system is considered work in thermodynamics. rechargable fan
When a thermodynamic system undergoes a process, the work done is always associated with a force. rechargable fan But in thermodynamics is more convenient to express the work function of the system state variables, and these will be different depending on the particular system we are considering, which may be difficult to recognize in the exchange interaction energy as I work. In these cases it is often useful classical thermodynamic definition of work given by Poincaré, which says that "the rechargable fan work is an interaction between a system and its surroundings, and is performed by the system if the only external effect to the boundaries of the system may consist in lifting a weight. "
However, we will limit our study to what is called hydrostatic or expansive system, is any system of constant mass exerted on the environment that surrounds a uniform hydrostatic pressure, in the absence of surface effects and action fields gravitational rechargable fan and electromagnetic, that is, in an expansive work system is due solely to a change rechargable fan in volume.
Consider a thermodynamic system of arbitrary shape and volume "V", acting on the external environment exerting forces due to hydrostatic pressure "pe", which assume uniform. The force that the external environment exerts rechargable fan on a surface element border "dS" is given by: DFE = - pe dS.
, Where the negative sign because the pressing force to the external environment has on the system is directed towards rechargable fan the interior of the system, while the surface element is represented to the outside, as the surface border a closed surface .
, Where the work is thus expressed infinitesimal differential third order, and considering that the scalar product given in the last equality represents the infinitesimal change in volume "dV" system globally, we can write: d~W = - pe dV.
If the system decreases in volume (dV <0) is due to receiving work, and the above expression leads to dW> 0, which agrees with the sign criteria adopted. Conversely, if the system is expanded (dV> 0), is the own system which does work on the medium, and according again to the equation, dW <0, which is also consistent with the approach of signs adopted.
For a finite rechargable fan process, when the system volume ranges from "Vi" value to a "Vf" value, the total energy in the form of work exchanged between the system and its environment verndrá given by: W = - (pe) dV from
The thermodynamic work is defined as the energy transferred between a system and its surroundings when the two a force is exerted. Numerically, the infinitesimal work "d~W" that makes a force "F" to the point of application suffer displacement "dr" is given by the expression: = F dr d~W.
If a system jointly or exerts a force on the surrounding environment and has a displacement of the point of application of the former, the work done by or on the system is called external work. If the work is done by one party over another is called inside job. In thermodynamics the internal work has no interest and only care about the external work, that is an interaction between a system and its outside environment.
In interactions experienced by thermodynamic sitemas, they can receive or give energy, because if the system receives is because the is giving the middle, or vice versa, it is necessary to establish a criterion of signs that allow us to interpret the results to be obtained. Thus, the IUPAC (acronym for the International Union of Pure and Applied Chemistry) recommended in 1970 that the same criteria be considered in Mechanics. This means that if the force is performed by the external environment on the system and displacement have the same sense, it is the system that increases your energy and, therefore, is said to have done work on the system and considered positive work. Conversely, if the work is done by the system on the exterior medium and the displacement is the same direction, the energy of the system decreases and it is considered negative working.
The thermodynamic definition of work is broader than the definition rechargable fan in mechanical terms indicated by the above equation. For example, the flow of electric current through the boundary of a system is considered work in thermodynamics. rechargable fan
When a thermodynamic system undergoes a process, the work done is always associated with a force. rechargable fan But in thermodynamics is more convenient to express the work function of the system state variables, and these will be different depending on the particular system we are considering, which may be difficult to recognize in the exchange interaction energy as I work. In these cases it is often useful classical thermodynamic definition of work given by Poincaré, which says that "the rechargable fan work is an interaction between a system and its surroundings, and is performed by the system if the only external effect to the boundaries of the system may consist in lifting a weight. "
However, we will limit our study to what is called hydrostatic or expansive system, is any system of constant mass exerted on the environment that surrounds a uniform hydrostatic pressure, in the absence of surface effects and action fields gravitational rechargable fan and electromagnetic, that is, in an expansive work system is due solely to a change rechargable fan in volume.
Consider a thermodynamic system of arbitrary shape and volume "V", acting on the external environment exerting forces due to hydrostatic pressure "pe", which assume uniform. The force that the external environment exerts rechargable fan on a surface element border "dS" is given by: DFE = - pe dS.
, Where the negative sign because the pressing force to the external environment has on the system is directed towards rechargable fan the interior of the system, while the surface element is represented to the outside, as the surface border a closed surface .
, Where the work is thus expressed infinitesimal differential third order, and considering that the scalar product given in the last equality represents the infinitesimal change in volume "dV" system globally, we can write: d~W = - pe dV.
If the system decreases in volume (dV <0) is due to receiving work, and the above expression leads to dW> 0, which agrees with the sign criteria adopted. Conversely, if the system is expanded (dV> 0), is the own system which does work on the medium, and according again to the equation, dW <0, which is also consistent with the approach of signs adopted.
For a finite rechargable fan process, when the system volume ranges from "Vi" value to a "Vf" value, the total energy in the form of work exchanged between the system and its environment verndrá given by: W = - (pe) dV from
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