Phase change equilibrium nature

Quantitative Aspects of Phase Changes Heat Involved in Phase Changes Equilibrium Nature of Phase Changes Phase Diagrams... 

Cryptands of type 7-9 and derivatives thereof carry alkali cations [6.4], even under conditions where natural or synthetic macrocycles are inefficient. The selec-tivities observed depend on the structure of the ligand, the nature of the cation and the type of cotransported counteranion. Designed structural changes allow the transformation of a cation receptor into a cation carrier [6.1, 6.4]. The results obtained with cryptands indicated that there was an optimal complex stability and phase-transfer equilibrium for highest transport rates. Combined with data for various other carriers and cations, they give a bell-shaped dependence of transport rates on extraction equilibrium (Fig. 11), with low rates for too small or too large... 

It is important to realize that not only does the solvent environment modify the equilibrium properties and the dynamics of the chemical process, it often changes the nature of the process and therefore the questions we ask about it. The principal object in a bimolecular gas phase reaction is the collision process between the molecules involved. In studying such processes we focus on the relation between the final states of the products and the initial states of the reactants, averaging over the latter when needed. Questions of interest include energy flow between different degrees of freedom, mode selectivity, and yields of different channels. Such questions could be asked also in condensed phase reactions, however, in most circumstances the associated observable cannot be directly monitored. Instead questions concerning the effect of solvent dynamics on the reaction process and the inter-relations between reaction dynamics and solvation, diffusion and heat transport become central. 

In this section, we examine the heat absorbed or released in a phase change and the equilibrium nature of the process. 

The nature of the phase changes and the conditions of equilibrium between matter in different states is a subject for detailed examination. 

Many phase changes occur around you every day, accompanied by the release or absorption of heat. When it rains, water vapor has condensed to a liquid, which changes back to a gas as puddles dry up. In the spring, solid water melts, and in winter, it freezes again. And the same changes take place, but faster, whenever you make a pot of tea or a tray of ice cubes. In this section, we quantify the heat involved in a phase change and examine the equilibrium nature of the process. 

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