Chemical components concept

Figure 2.3 outlines the basic concept of a redox process involving the chemical components A, B, C and D. The oxidation of component A (electron donor) to component C produces an electron. This electron is transferred to the reduction step, thereby initiating transformation of component B (electron acceptor) into component D. The total redox process is shown in Figure 2.3. 

The concept of a Markov process is not restricted to one-component processes Y(t but applies to processes Y(t) with r components as well. Examples the three velocity components of a Brownian particle the r chemical components of a reacting mixture. The following remark, however, is essential. 

The results of the discussion on the phenomenological thermodynamics of crystals can be summarized as follows. One can define chemical potentials, /jk, for components k (Eqn. (2.4)), for building units (Eqn. (2.11)), and for structure elements (Eqn, (2.31)). The lattice construction requires the introduction of structural units , which are the vacancies V,. Electroneutrality in a crystal composed of charged SE s requires the introduction of the electrical unit, e. The composition of an n component crystal is fixed by n- 1) independent mole fractions, Nk, of chemical components. (n-1) is also the number of conditions for the definition of the component potentials juk, as seen from Eqn. (2.4). For building units, we have (n — 1) independent composition variables and n-(K- 1) equilibria between sublattices x, so that the number of conditions is n-K-1, as required by the definition of the building element potential uk(Xy For structure elements, the actual number of constraints is larger than the number of constraints required by Eqn. (2.18), which defines nk(x.y This circumstance is responsible for the introduction of the concept of virtual chemical potentials of SE s. 

Consider a material or system that is not at equilibrium. Its extensive state variables (total entropy number of moles of chemical component, i total magnetization volume etc.) will change consistent with the second law of thermodynamics (i.e., with an increase of entropy of all affected systems). At equilibrium, the values of the intensive variables are specified for instance, if a chemical component is free to move from one part of the material to another and there are no barriers to diffusion, the chemical potential, q., for each chemical component, i, must be uniform throughout the entire material.2 So one way that a material can be out of equilibrium is if there are spatial variations in the chemical potential fii(x,y,z). However, a chemical potential of a component is the amount of reversible work needed to add an infinitesimal amount of that component to a system at equilibrium. Can a chemical potential be defined when the system is not at equilibrium This cannot be done rigorously, but based on decades of development of kinetic models for processes, it is useful to extend the concept of the chemical potential to systems close to, but not at, equilibrium. 

In this chapter, we make preparations for performing a thermodynamic analysis of a process. The principles of such an analysis are defined first. From the calculation of the minimum, also called the ideal amount of work to perform a certain task, the convenience, not the necessity, of defining the concept of exergy is made plausible. Exergy can have a physical and a chemical component. The quality of the Joule is another convenient concept for a clear analysis and for conclusions on process performance. 

The concept of chemical components. Each species can be expressed as the product of a set of chemical components that define the equilibrium problem and a formation constant. Morel (1983) has expressed the definition of the chemical components as a set of chemical entities that permits a complete description of the stoichiometry of the system . For the example of the hydroxy-aluminium species given above Al3+ and H+ are the chemical components. As will be seen in the section on surface complexes the components are not necessarily elements or species. The components concept is important for understanding how to set up chemical equilibrium problems with various computer models. 

To analyze reaction (6.22) in the framework of the chemical interference concept, it should be divided into two component processes the primary and the secondary overall reactions. 

This is an important concept and is generic to many chemical processes. From the viewpoint of individual units, chemical component bal ancing is not a problem because exit streams from the unit automatically adjust their flows and compositions. However, when we connect units together with recycle streams, the entire system behaves almost like a pure integrator in terms of the reactants. If additional reactant is fed into the system without changing reactor conditions to consume the reactant, this component will build up gradually within the plant because it has no place to leave the system. 

Jim Downs (1992) of Eastman Chemical Company has insightfully pointed out the importance of looking at the chemical component balances around the entire plant and checking to see that the control structure handles these component balances effectively. The concepts of overall component balances go back to our first course in chemical engineering, where we learned how to apply mass and energy balances to any system, microscopic or macroscopic. We did these balances for individual unit operations, for sections of a plant, and for entire processes. 

The chemical potential concept provides a useful way to think about the tendency for spontaneous chemical change in complex environmental systems involving gases, liquids, and solids (cf. Wood and Fraser 1976 Stumm and Morgan 1981). In a particular phase, the chemical potential, /U, of component i is related to the activity of i through the expression... 

The key concept for the adaptation of these electroanalytical techniques was Clark s idea of encapsulating the electrodes and supporting chemical components... 

Hundreds of scientific articles (many of them referenced in this text) have stated that tobacco and tobacco smoke are complex mixtures. This is an accurate statement. But some have alluded to or emphasized that they are primarily complex, that is, these mixtures of chemicals are just too multifarious, too difficult to completely understand, or so complicated and/or convoluted that the normal individual could not possible comprehend the totality of the concept or composition of the mixture. This was never the intent of the definition of a complex mixture, but nevertheless, some have implied that this multifaceted conglomeration of chemical components in tobacco and tobacco smoke is too difficult to explain and understand. The tobacco industry has often stated that tobacco and tobacco smoke are complex mixtures, without providing a basis for the statement. This text illustrates the complexity of tobacco and tobacco smoke. It provides the reader with an historical perspective on the identification of thousands of chemical components in tobacco and tobacco smoke, it contains reviews of all known and identified classes of chemical components in tobacco and tobacco smoke, and it provides thousands of accessible references on identified chemical components in tobacco and tobacco smoke. Also provided in the preceding pages are references and discussions of one of the major problems with a complex mixture, that is, the extrapolation of a biological property found in experimental studies with an individual compound in the mixture to the property of that component in a mixture which may contain... 

The essential character of thermal phenomena becomes clear, the conditions of coexistence of solids, liquids, and gases in systems of any number of chemical components are explained, the dependence of equilibria upon concentrations, upon pressure, and upon temperature is defined. The conceptions of entropy and free energy, of statistical equilibrium and energy distribution, provide quantitative laws which describe the perpetual conflict of order and chaos, and which prescribe in a large measure not only the shapes assumed by the material world but also the pattern of its possible changes. 

Applying the widely-used chemical thermodynamics concept of free energy linearity, it is easy to demonstrate that any characteristic y which linearly depends on free energy or on free activation energy of process in the mixed solvent composed of specifically non-interacting components, shall be linear function of the components with partial molar concentration X. 

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