Macroscopic topics chemical kinetics

The topic of interactions between Lewis acids and bases could benefit from systematic ab initio quantum chemical calculations of gas phase (two molecule) studies, for which there is a substantial body of experimental data available for comparison. Similar computations could be carried out in the presence of a dielectric medium. In addition, assemblages of molecules, for example a test acid in the presence of many solvent molecules, could be carried out with semiempirical quantum mechanics using, for example, a commercial package. This type of neutral molecule interaction study could then be enlarged in scope to determine the effects of ion-molecule interactions by way of quantum mechanical computations in a dielectric medium in solutions of low ionic strength. This approach could bring considerable order and a more convincing picture of Lewis acid base theory than the mixed spectroscopic (molecular) parameters in interactive media and the purely macroscopic (thermodynamic and kinetic) parameters in different and varied media or perturbation theory applied to the semiempirical molecular orbital or valence bond approach [11 and references therein]. 

Reviewed herein are some of the fundamental concepts associated with chemical equilibrium, chemical thermodynamics, chemical kinetics, aqueous solutions, acid-base chemistry, oxidation-reduction reactions and photochemistry, all of which are essential to an understanding of atmospheric chemistry. The approach is primarily from the macroscopic viewpoint, which provides the tools needed by the pragmatist. A deeper understanding requires extensive treatment of ihe electronic structure of matter and chemical bonding, topics that are beyond the scope of this introductory text. This book can be used for either self-instruction, or as the basis for a short introductory class... 

The chemical change as observed in a macroscopic experiment is the result of many molecular collisions. In Section 3.1.2 we define the reaction cross-section from the macroscopic observable rate of reactive collisions. This is sufficient to discuss the dependence of the cross-section on the collision energy. Then we discuss the temperature dependence of the reaction rate as arising from this energy dependence. To understand the origin of the energy needs of chemical reactions, we provide, in Section 3.2, a microscopic interpretation of the reaction cross-section. Finally, a caveat. In this chapter we are not taking accoimt of the internal structure of the reactants. This key topic has to wait imtil Chapter 5. The only concession is that an appendix provides an extension of chemical kinetics to the important special case where we do resolve internal states. 

In preparing the sixth edition, we have revised the textbook extensively to meet these present-day needs. In particular, we believe that the most logical sequence of topics begins with the physical properties and structure of atoms is followed by structure, bonding, and properties of molecules proceeds to describe macroscopic collections of atoms and molecules continues with a discussion of chemical properties and reactions under equilibrium conditions and finishes with dynamics and kinetics. 

In this chapter we shall be concerned with the basic principles that govern the crystallization behavior of flexible long-chain molecules. The more-rigid type of polymers will be discussed in Chapter 5. The subject matter divides itself naturally into several interrelated subdivisions. These include thermodynamics of crystallization, kinetics and mechanisms of crystallization, structure and morphology, and microscopic and macroscopic properties. We shall discuss each of these topics in terms of fundamental physical and chemical concepts. There is an interrelation among the various aspects of polymer crystallization as is indicated by the chart given in Fig. 4.1. 

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