Solids mixing real mixtures

Furthermore, the real mixture may be less compressible than the ideal one and behaves as if the mixed films were solid (see Figure 2 for the mixture with molar fraction of component 2 equal to 0.5). This difference in behavior results from the difference in the compressibilities of the pure and mixed constituents 1 and 2. It shows that the interaction of the constituents in the mixed film can modify their state. We have deduced the variation of the state of CTAB (1) by mixing, applying the following approach appropriate to penetration. 

The thermodynamic functions for the gas phase are more easily developed than for the liquid or solid phases, because the temperature-pressure-volume relations can be expressed, at least for low pressures, by an algebraic equation of state. For this reason the thermodynamic functions for the gas phase are developed in this chapter before discussing those for the liquid and solid phases in Chapter 8. First the equation of state for pure ideal gases and for mixtures of ideal gases is discussed. Then various equations of state for real gases, both pure and mixed, are outlined. Finally, the more general thermodynamic functions for the gas phase are developed in terms of the experimentally observable quantities the pressure, the volume, the temperature, and the mole numbers. Emphasis is placed on the virial equation of state accurate to the second virial coefficient. However, the methods used are applicable to any equation of state, and the development of the thermodynamic functions for any given equation of state should present no difficulty. 

Virtually aU the gases, liquids, and solids in the real world are mixtures—two or more substances mixed together physically, not combined chemically. Synthetic mixtures, such as glass and soap, usually contain only a dozen or so components, but natural mixtures, such as seawater and soil, often contain over 50. Living mixtures, such as trees and students, are the most complex—even a simple bacterial cell contains well over 5000 different compounds (Table 13.1). 

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