Transfers, Transformations, and Equilibria

When two or more homogeneous systems are brought into contact to form a single heterogeneous system, any of several actions may occur before equilibrium is reestablished. The possibilities include mass and energy transfers, chemical reactions, and the appearance or disappearance of phases. In this chapter we provide thermodynamic criteria for determining whether and to what extent such phenomena actually occur. Surprisingly, these criteria invoke no new thermodynamics—we need only combine familiar thermodynamic quantities in new ways and, in some cases, apply to those quantities mathematical operations that we have not used heretofore. 

The heterogeneities of most concern to us are those that involve the presence of more than one phase. The analysis of multiphase systems can be important to the design and operation of many industrial processes, especially those in which multiple phases influence chemical reactions, heat transfer, or mixing. For example, phase-equilibrium calculations form the bases for many separation processes, including stagewise operations, such as distillation, solvent extraction, crystallization, and supercritical extraction, and rate-limited operations, such as membrane separations. 

Analysis of multiphase systems is a principal theme of chemistry and chemical engineering another is analysis of chemical reactions— processes in which chemical bonds are rearranged among species. Rearranging chemical bonds is the most efficient way to store and release energy, it drives many natural processes, and it is used industrially to make substitutes for, and concentrated forms of, natural products. 

The chapter divides in two in early sections we describe the behavior of nomeact-ing systems, while in later sections we deal with systems in which reactions occur. In 7.1 we combine the first and second laws to obtain criteria for identifying limitations on the directions of processes and for identifying equilibrium in closed multiphase systems. Then in 7.2 we develop the analogous relations for heat, work, and material transfers in open systems. With the material in 7.2 as a basis, we then present in 7.3 the thermodynamic criteria for equilibrium among phases. 

A similar program is used for reacting systems. In 7.4 we extend the combined first and second laws to closed systems xmdergoing chemical reactions, then in 7.5 we show how the combined laws apply to reactions in open systems. In 7.6 we formulate the thermodynamic criterion for identifying reaction equilibria. By presenting 

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