Keywords: First Law, symmetry, reversible process, entropy.Д¬omo Г© referido na literatura, , a variaГ§ГЈo de entropia, D S, em um processo irreversГvel Г© determinada substituindo o processo em causa por um outro, reversГvel, que leve o sistema entre os mesmos estados de equilГbrio. Then, simulations of an irreversible ideal gas process are presented using MathematicaВ©, 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. In contrast, the concept of work reservoir is not mentioned very often in the literature. The concept of heat reservoir is indeed required to set up the formalism of Thermodynamics, and this is sufficiently emphasized in textbooks (see Refs. 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 literature 2 2 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. Joaquim Anacleto 1 Department, University of TrГЎs-os-Montes e Alto Douro, Vila Real, PortugalДЄs is stressed in literature, , the entropy change, D S, 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.

Primeira Lei simetria processo reversГvel entropiaД®ntropy change of an ideal gas determination with no reversible processДeterminaГ§ГЈo da variaГ§ГЈo de entropia num gГЎs ideal sem usar um processo reversГvel Seguidamente, considerando um gГЎs ideal, apresentamos simulaГ§Гµes de um processo irreversГvel, usando o MathematicaВ©, que cremos serem de valor pedagГіgico, porque comprovam as idГ©ias expostas e clarificam possГveis questГµes relacionadas com o difГcil conceito de entropia. ComeГ§ando por explorar brevemente as simetrias associadas Г primeira lei da TermodinГўmica, obtemos uma equaГ§ГЈo que relaciona variГЎveis do sistema com variГЎveis da vizinhanГ§a e que nos permite determinar a variaГ§ГЈo de entropia sem se recorrer a nenhum processo reversГvel auxiliar. Outra motivaГ§ГЈo para este artigo Г© sublinhar a relevГўncia do conceito de reservatГіrio, em particular o de reservatГіrio de trabalho, que Г© usualmente ignorado na literatura2. Tentamos desmistificar esta idГ©ia, mostrando que podemos preservar o processo original. Contudo, pode tambГ©m sugerir aos estudantes a idГ©ia de que este procedimento Г© obrigatГіrio. Isto pode ser feito pois a entropia Г© uma funГ§ГЈo de estado. ДЇirst Law symmetry reversible process entropyД¬omo Г© referido na literatura, , a variaГ§ГЈo de entropia, deltaS, em um processo irreversГvel Г© determinada substituindo o processo em causa por um outro, reversГvel, que leve o sistema entre os mesmos estados de equilГbrio.

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. 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.

Entropy units