Variação de entropia na termalização espontânea de dois blocos distintos revisitada

Abstract

In a recent article (Revista Brasileira de Ensino de Física, first refrence of this note), F. Lima presented an expression for the change of entropy of a closed system constituted by two distinct blocks in the thermalization process which occurs when the blocks, initially with different temperatures, are put in thermic contact. From this he showed, using differential calculus, that this change of entropy is positive, in full agreement with the entropic version of the second law of thermodynamics. In this note we presented an alternative demonstration. Initially we deduced, in an elementary level, the final state of thermal equilibrium of system from nullity of the first derivative of entropy. Then we showed that the entropy of the system is increasing. Finally we showed, from the second derivative of entropy, that the final equilibrium state of system is a state of maximum entropy and therefore we have a positive change of entropy.