Chemical component definition

Water and hydrocarbons occurring together, in shallow aquifer systems, may be considered immiscible for flow calculation purposes however, each is somewhat soluble in the other. Since groundwater cleanup is the purpose behind restorations, it receives greater attention. Definition of water quality based on samples retrieved from monitoring wells relies heavily upon the concentration of individual chemical components found dissolved in those samples. An understanding of the processes that cause concentration gradients is important for the proper interpretation of analytical results. 

In the definition of c, one must generally assume that any chemical component is free to penetrate into any phase, even if the partitioning between phases varies strongly from component to component. Hence, c is the number of independent chemical components found in any phase, to account for the limiting case in which different chemical components partition completely (within limits of experimental detection) into different phases. 

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. 

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. 

Solid phases of binary systems, like the liquid phases, are very commonly of variable composition. Here, as with the liquid, the stable range of composition is larger, the more similar the two components are. This of course is quite c-ontrary to the chemists notion of definite chemical composition, definite structural formulas, etc., but those notions are really of extremely limited application. It happens that the solid phases in the system water—ionic compound are often of rather definite composition, and it is largely from this rather special case that the idea of definite compositions in solids has become so firmly rooted. In such a system, there are normally two solid phases ice and the crystalline ionic compound. Ice can take up practically none of any ionic compound, so that it has practically no range of compositions. And many ionic crystals... 

Let us recall the analytic formulation of the value of chemical potential p of a chemical component A in media with a different phase state. By definition,... 

The most useful result of multivariate analysis procedures is the reduction in apparent dimensionality of the data. From an initial collection of several hundred mass peaks, the data are reduced to only a few factors, each of which is by definition a linear combination of the original mass peak intensities. By plotting these linear combinations in the form of spectra, significant information about the chemical components underlying the factors can be obtained. Often this requires rotation of the factors in order to optimize the chemical component patterns. 

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 operational definition of y via a small change in surface area may conceptually be connected with a concomitant change in the concentration of one or several of the chemical components, AUi, in the second phase. To keep all concentrations (intensive variables) constant, the amount of An has to be replenished in that phase by adding it to the system through a leak, keeping T and V constant. The only place where the small amount of component i can go is the incremental increase in interfacial area, AA. This operation therefore defines the adsorption of component i on the interface between the two phases 1 and 2. The adsorbed amount per unit area is called the surface excess, equal to... 

The meaning of this definition is that no chemical component causes the decrease of another one. Nothing has been supposed about the effect of components on themselves. Our definition is in concord with the definitions used in classical chemical kinetics (cf. Bazsa Beck, 1971). A mechanism is called canonically cross-catalytic, if for all the sets of reaction rate constants the canonic complex chemical reaction corresponding to the induced kinetic differential equation of the complex chemical reaction is cross-catalytic. 

Suppose you have a system you want to describe thermodynamically. How do you do it Perhaps most important in your description is what s in the system that is, the components of the system. For our purposes, a component is defined as a unique chemical substance that has definite properties. For example, a system composed of pure UFg has a single chemical component uranium hexafluoride. Granted, UFg is composed of two elements, uranium and fluorine, but each element lost its individual identity when the compound UFg was formed. The phrase chemically homogeneous can be used to describe single-component systems. 

The scope of this review is limited largely to the newer techniques employed to characterize natural products by mass spectrometry. However, in order to maintain a reasonable perspective on the subject the older, more established techniques are introduced in those instances where their application is preferred for a particular compound class. The definition of natural products is taken to include chemical components of, and products from, plant and animal systems. 

The term feedstock in this article refers not only to coal, but also to products and coproducts of coal conversion processes used to meet the raw material needs of the chemical industry. This definition distinguishes between use of coal-derived products for fuels and for chemicals, but this distinction is somewhat arbitrary because the products involved in fuel and chemical appHcations are often identical or related by simple transformations. For example, methanol has been widely promoted and used as a component of motor fuel, but it is also used heavily in the chemical industry. Frequendy, some or all of the chemical products of a coal conversion process are not isolated but used as process fuel. This practice is common in the many coke plants that are now burning coal tar and naphtha in the ovens. 

From the definition of a partial molar quantity and some thermodynamic substitutions involving exact differentials, it is possible to derive the simple, yet powerful, Duhem data testing relation (2,3,18). Stated in words, the Duhem equation is a mole-fraction-weighted summation of the partial derivatives of a set of partial molar quantities, with respect to the composition of one of the components (2,3). For example, in an / -component system, there are n partial molar quantities, Af, representing any extensive molar property. At a specified temperature and pressure, only n — 1) of these properties are independent. Many experiments, however, measure quantities for every chemical in a multicomponent system. It is this redundance in reported data that makes thermodynamic consistency tests possible. 

Purification of a chemical species by solidification from a liquid mixture can be termed either solution crystallization or ciystallization from the melt. The distinction between these two operations is somewhat subtle. The term melt crystallization has been defined as the separation of components of a binaiy mixture without addition of solvent, but this definition is somewhat restrictive. In solution crystallization a diluent solvent is added to the mixture the solution is then directly or indirec tly cooled, and/or solvent is evaporated to effect ciystallization. The solid phase is formed and maintained somewhat below its pure-component freezing-point temperature. In melt ciystallization no diluent solvent is added to the reaction mixture, and the solid phase is formed by cooling of the melt. Product is frequently maintained near or above its pure-component freezing point in the refining sec tion of the apparatus. 

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