Azeotropy surface

This book is the first volume of a Treatise on Thermodynamics based on the methods of Gibbs and De Donder. It deals with the following topics fundamental theorems, homogeneous systems, heterogeneous systems, stability and moderation, equilibrium displacements and equilibrium transformations, solutions, azeotropy, and indifferent states. The second volume deals with surface tension and adsorption while the third and last will be concerned with irreversible phenomena. 

These azeotropy expressions 2.19 state that in the space of transformed composition variables the bubble-point and dew-point surfaces are tangent at an azeotropic state (Barbosa and Doherty, 1988a), allowing the azeotropes to be found easily by visual inspection in the reactive phase diagram for the case of Uc — rirx < 3 (figure 2.4). For systems beyond this space, a graphical determination of azeotropes might not be feasible. 

An isothermal extremum in a, that is a state of the liquid system at which (daidn )T.( is zero for all components is the surface analogue of an azeotrope,at whidi the vapour pressure is at an extremum. (We use here the conventional sense of the word azeotrope, see Appendix 1.) It follows from (2.45) that surface azeotropy implies that all relative adsorptions, (p-rj-plFj), are zero. 

Analogously, in an interface we may have distinct surface phases with first-order transitions between them. Ihat occurs when, for a given set of values of the themrodynamic fields, an interface has two alternative structures of equal tension. Hie two structures differ in their microscopic composition profiles, and therefore also (except for occasional azeotropies) in their macroscopic adsorptions (surface excesses). We may take... 

Azeotropies do not necessarily occur the foregoing are merely limitations on their occurrence. On the other hand, they can always be made to occur by a suitable choice of fields. With each point the two-phase coexistence surface we may associate a new coordinate system in which any number up to c of the coordinate axes is diosen parallel to... 

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