Começando por explorar brevemente as simetrias associadas à primeira lei da Termodinâmica, obtemos uma equação que relaciona variáveis do sistema com variáveis da vizinhança e que nos permite determinar a variação de entropia sem se recorrer a nenhum processo reversível auxiliar. Outra motivação para este artigo é sublinhar a relevância do conceito de reservatório, em particular o de reservatório de trabalho, que é usualmente ignorado na literatura2. Tentamos desmistificar esta idéia, mostrando que podemos preservar o processo original. Contudo, pode também sugerir aos estudantes a idéia de que este procedimento é obrigatório. Isto pode ser feito pois a entropia é uma função de estado. įirst Law symmetry reversible process entropyĬomo é referido na literatura, , a variação de entropia, deltaS, em um processo irreversível é determinada substituindo o processo em causa por um outro, reversível, que leve o sistema entre os mesmos estados de equilíbrio. Then, simulations of an irreversible ideal gas process are presented using Mathematica©, which we believe to be of pedagogical value in emphasizing the exposed ideas and clarifying some possible misunderstandings relating to the difficult concept of entropy. Starting by exploring briefly the symmetries associated to the first law of Thermodynamics, we obtain an equation which relates both the system and neighborhood variables and allows entropy changes determination without using any auxiliary reversible process. Another motivation for this paper is to emphasize the relevance of the reservoirs concept, in particular the work reservoir, which is usually neglected in the literature2. We try to demystify this idea, showing that we can preserve the original process. However this may suggest to the students the idea that this procedure is mandatory. This can be done since entropy is a state function. I will continue if you feel that it is.As is stressed in literature, , the entropy change, deltaS, during a given irreversible process is determined through the substitution of the actual process by a reversible one which carries the system between the same equilibrium states. I'm going to stop here before presenting more to see if this initial part of the development is along the lines that you were seeking. An analogous, although more complicated, equation can be written for a Newtonian (viscous) fluid in terms of viscosity and velocity gradients. This is the differential from of the heat conduction equation we all learned in freshman physics. One definition of entropy change is $dS = \delta q_$$ where the value of k is measured or derived from molecular dynamics and statistical thermodynamics consideration. The former is defined as a path where the system and its surroundings are in exact thermodynamic equilibrium at all points during the process. Two types of paths are defined: reversible and irreversible. The change in the universe is the sum of the changes in the system and its surroundings, so only two of the three are independent.Īny change in any thermodynamic state function is always independent of the path taken. The something of interest here is a thermodynamic state function of a system, its surroundings, or the universe. It means an infinitesimal change in something as it undergoes a process.
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