Irreversible thermodynamics basic postulate

The basic postulate of irreversible thermodynamics is that, near equilibrium, the local entropy production is nonnegative ... 

The latter form is the basic equation of diffusion generally identified as Fick s first law, formulated in 1855 [13]. Fick s first law, of course, can be deduced from the postulates of irreversible thermodynamics (Section 3.2), in which fluxes are linearly related to gradients. It is historically an experimental law, justified by countless laboratory measurements. The convergence of all these approaches to the same basic law gives us confidence in the correctness of that law. However, the approach used here gives us something more. 

In this chapter, we will mainly consider the Gibbsian thermodynamics of phase equilibria relevant to problems in hydrocarbon reservoirs and use its concepts in the other chapters to solve practical problems. The thermodynamics of equilibrium processes also provide the framework for nonequilibrium and irreversible thermodynamics. It is our intention that the material covered in this book should be self-contained. The postulational approach introduced by Callen (1985), and Tisza (1966) is, therefore, adopted to make brief the presentation of basic concepts and equations. 

The constant growth of entropy postulated in the second law is closely related to the following principle By the irreversible process the system is spontaneously directed towards the most frequently occurring set of micro states which corresponds to the same macro state of the system. The macroscopic state of equilibrium - where entropy is at its maximum - is the state which is linked to the largest number of different micro states. This basic concept is the basis of the Boltzmann relation that defines the entropy function S in statistical thermodynamics. 

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