A Whole New Phase

One of the most important concepts in chemistry is that of chemical equilibrium. Unfortunately, it is also one of the more complex and can be confounding. To avoid this dilemma, we will approach the topic incrementally. We have already taken a major step by delving into the subject of thermodynamics. We now take the second step by discussing phase equilibrium, a less complicated and more familiar phenom- 

The process of going directly from solid to gas phase is called sublimation. Deposition is the process of going from the gas phase directly to a solid. An example of deposition might be frost under certain conditions, water vapor in the air will deposit as frost without condensing to a liquid first. Sublimation and its companion process, deposition, are shown in figure 1.14.1 along with the common phases of matter and the processes that connect them. 

If that were all there were to the story, this would be a short chapter and chemistry would be considerably less rich. But as we mentioned above, pressure plays an integral role in the wide-ranging behaviors of various materials, which adds another dimension to the discussion. In a mixture, composition also has to be considered, which adds one more factor. Pressure accounts for why ice skating is fun but dry-ice skating is not, and the composition consideration addresses why good pizza goes bad. WeTl start with ice skating and have pizza later. 

When water boils on the stove, it undergoes a phase change from liquid to vapor. Bubbles are pockets of vapor that form in the water as it evaporates. The pressure inside the bubbles is the same as the pressure pushing down on the water, otherwise they could not rise and the water would not boil. When pressure is reduced over a liquid, the liquid can boil 

The phase diagram displays those regions of temperature and pressure that result in the various phases of water gas, solid, and liquid. The lines between the phases represent the conditions under which the material is in equilibrium, that is, it could just as happily be in either phase, so some amount will be in one 

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The success in determining the chemical structure of qinghaosu is only one example of the accomplishments of chemists in attaining a better understanding of the relationship between the chemical structure of natural drugs and their pharmacological effects. Those accomplishments have formed the basis of a whole new phase of the pharmaceutical industry in which natural products and their derivatives provide an extensive source of new drugs. 

Memfield s concept of a solid phase method for peptide synthesis and his devel opment of methods for carrying it out set the stage for an entirely new way to do chem ical reactions Solid phase synthesis has been extended to include numerous other classes of compounds and has helped spawn a whole new field called combinatorial chemistry Combinatorial synthesis allows a chemist using solid phase techniques to prepare hun dreds of related compounds (called libraries) at a time It is one of the most active areas of organic synthesis especially m the pharmaceutical industry... 

Unfortunately, most of the elements chosen as promising propellant ingredients are metals and hence solids rather than liquids. The endeavor to incorporate solid-phase metals and metal compounds into liquid propellants has led to a whole new area of propellant technology. Heterogeneous fuels are discussed in detail later. 

BASF s original acid scavenger, triethylamine, created viscosity and work-up problems because of the need to maintain anhydrous conditions. BASF s use of 1-methylimidazole instead of triethylamine, at their reaction temperature of 80°C, led to the formation of two liquid phases, an upper diethoxyphenylphosphine phase, and a lower methylimidazolium chloride phase (fortuitously, this ionic liquid melts at 75°C ). Moreover, methylimidazolium chloride proved to be a nucleophilic catalyst. The processing revolution generated by these discoveries enabled creation of a high-productivity continuous process for diethoxyphenylphosphine manufacture and created a whole new business in acid scavenging technology. 

Mn. This opens up a whole new dimension of complexity in both bulk and surface electronic structure. Bulk phases of most of the oxidation states are sta-... 

Polymer science has expanded over the past few decades and shifted its centre of interest to encompass a whole new range of materials and phenomena. Fundamental investigations on the molecular structure of polymeric liquids, gels, various phase transitions, alloys and blends, molecular motion, flow properties, and many other interesting topics, now constitute a signiflcant proportion of the activity of physical and chemical laboratories around the world. 

Recently, however, it has become possible to study ionic reactions in the gas phase, where of course there can be no interference by solvation. This work has already led to the development of a whole new area of chemistry and one in which a variety of novel phenomena occur. Before discussing these in terms of the PMO approach, we may first consider briefly the techniques used in their study. 

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