Stoichiometry Description of the quantitative

Stoichiometry Description of the quantitative relationships among elements in compounds (composition stoichiometry) and among substances as they undergo chemical changes (reaction stoichiometry). 

The G.F.F. theory was put to a more quantitative test by Luckhurst and OrgeF " who examined the electron spin resonance spectrum of fluorenone ketyl, generated by electrochemical reduction, in mixtures of dimethylformamide and methanol. In the range of mol fractions of methanol less than 0.15, the G.F.F. theory was able to account for the variation of all four observed splitting constants on the assumption that the alcohol and the ketyl formed a 1 1 adduct. In this region of alcohol concentrations the dimethylformamide is in excess and it is not necessary to postulate a stoichiometry for the solvation of the ketyl by dimethylformamide. At concentrations of methanol in excess of 0.15 the above description of the system was found to be inadequate, presumably because of the formation of l 2ketyl-alcohol adducts or because of a more general form of solvent effect upon the 1 1 adduct. 

Heischer et al. [172] measured the interfacial tension reductirai credited to the complexation between carboxy-terminated PBD and amine-terminated PDMS, which were added to an immiscible blend of PBD and PDMS. The changes in interfacial tensimi resembled the behavior observed for block copolymer addition to homopolymer blends there is initially a linear decrease in interfacial tension with the concentration of functional homopolymer up to a critical concentration, at which the interfacial tension becomes invariant to further increases in the concentration of functional material. However, the formation of interpolymer complexes depends on the equilibrium between associated and dissociated functional groups and, thus, the ultimate plateau value for interfacial tension reduction is dependent on the functional group stoichiometry. A reaction model for end-complexation was developed in order to reproduce the interfacial tension reduction data with Fourier transform infrared spectroscopy applied to determine the appropriate rate constants. The model provided a reasonable qualitative description of the interfacial tension results, but was not able to quantitatively predict the critical compositions observed experimentally. 

For a quantitative description of the behavior of gases, we will employ some simple gas laws and a more general expression called the ideal gas equation. These laws will be explained by the kinetic-molecular theory of gases. The topics covered in this chapter extend the discussion of reaction stoichiometry from the previous two chapters and lay some groundwork for use in the following chapter on thermochemistry. The relationships between gases and the other states of matter— liquids and solids—are discussed in Chapter 12. 

The chemical reactor has a determinant role on both the material balance and the structure of the whole flowsheet. It is important to stress that the downstream levels in the Hierarchical Approach, as the separation system and heat integration, depend entirely on the composition of the reactor exit stream. However, a comprehensive kinetic model of the reaction network is hardly available at an early conceptual stage. To overcome this shortcoming, in a first attempt we may neglect the interaction between the reactor and the rest of the process, and use an analysis based on stoichiometry. A reliable quantitative relationship between the input and the output molar flow rates of components would be sufficient. This information is usually available from laboratory studies on chemistry. Kinetics requires much more effort, which may be justified only after proving that the process is feasible. Note that the detailed description of stoichiometry, taking into account the formation of sub-products and impurities is not a trivial task. The effort is necessary, because otherwise the separation system will be largely underestimated. 

This chapter is modeled after the MAB Report, updating and expanding the coverage to correspond to the state of the art in January 1973. A short description of various analytical techniques used to obtain composition information on materials is followed by a tabular summary of sensitivities and precisions of these techniques. The next section describes the application of these techniques to specific characterization problems such as stoichiometry, homogeneity, and oxidation state, as well as survey and quantitative methods of measuring impurities. Finally, examples are given from the literature of detailed studies on a number of high-purity materials to illustrate the present state of the art of characterization of practical samples. 

---