System heterogeneous

The equivalent equations for heterogeneous and quasi-heterogeneous systems (tire latter are small vesicles which can practically be handled as homogeneous systems, but which are nevertlieless large enough to possess a macroscopic solid-liquid interface) are dealt witli in section C2.14.7. 

The mechanical shaking machine is employed for auto matic mixing of heterogeneous systems and finds many applications in the organic chemistry laboratory. 

Rate of polymerization. The rate of polymerization for homogeneous systems closely resembles anionic polymerization. For heterogeneous systems the concentration of alkylated transition metal sites on the surface appears in the rate law. The latter depends on the particle size of the solid catalyst and may be complicated by sites of various degrees of activity. There is sometimes an inverse relationship between the degree of stereoregularity produced by a catalyst and the rate at which polymerization occurs. 

The vapor is thea withdrawa from the stiH as distillate. The changing Hquid composition is most coavenieafly described by foUowiag the trajectory (or residue curve) of the overall composition of all the coexistiag Hquid phases. An exteasive amouat of valuable experimental data for the water—acetoae—chloroform mixture, including biaary and ternary LLE, VLE, and VLLE data, and both simple distillation and batch distillation residue curves are available (93,101). Experimentally determined simple distillation residue curves have also been reported for the heterogeneous system water—formic acid—1,2-dichloroethane (102). 

CHEMILUMINESCENCE REACTIONS IN HETEROGENEOUS SYSTEMS FOR TRACE DETERMINATION OF BIOLOGICALLY... 

Present research is devoted to investigation of application of luminol reactions in heterogeneous systems. Systems of rapid consecutive reactions usable for the determination of biologically active, toxic anions have been studied. Anions were quantitatively converted into chemiluminescing solid or gaseous products detectable on solid / liquid or gas / liquid interface. Methodology developed made it possible to combine concentration of microcomponents with chemiluminescence detection and to achieve high sensitivity of determination. 

The phase rule is a mathematical expression that describes the behavior of chemical systems in equilibrium. A chemical system is any combination of chemical substances. The substances exist as gas, liquid, or solid phases. The phase rule applies only to systems, called heterogeneous systems, in which two or more distinct phases are in equilibrium. A system cannot contain more than one gas phase, but can contain any number of liquid and solid phases. An alloy of copper and nickel, for example, contains two solid phases. The rule makes possible the simple correlation of very large quantities of physical data and limited prediction of the behavior of chemical systems. It is used particularly in alloy preparation, in chemical engineering, and in geology. 

There are a large number of processes in the chemical industries that handle a variety of suspensions of solid particles in liquids. The application of filtration techniques for the separation of these heterogeneous systems is sometimes very costly. If, however, the discrete phase of the suspension largely contains settleable particles, the separation can be effected by the operation of sedimentation. The process of sedimentation involves the removal of suspended solid particles from a liquid stream by gravitational settling. This unit operation is divided into thickening,... 

If, for a given heterogeneous system, the settling veloeity of the smallest particles that will separate out is u and the height of the ehamber (or the distanee between horizontal plates) is H, then the settling time will be H/u. The time required for a... 

The Archimedes number contains parameters that characterize the properties of the heterogeneous system and the criterion establishing the type of settling. The criterion of separation essentially establishes the separating capacity of a sedimentation machine. The product of these criteria is ... 

The differential reactor is used to evaluate the reaction rate as a function of concentration for a heterogeneous system. It consists of a tube that contains a small amount of catalyst as shown schematically in Figure 4-17. The conversion of the reactants in the bed is extremely small due to the small amount of catalyst used, as is the change in reactant concentration through the bed. The result is that the reactant concentration through the reactor is constant and nearly equal to the... 

Information on the composition and temperature changes is obtained from the rate equation, while the mixing patterns are related to the intensity of mixing and reactor geometry. Heat transfer is referred to as the exothermic or endothermic nature of the reactions and the mass transfer to the heterogeneous systems. 

Heterogeneous reaetions involve two or more phases. Examples are gas-liquid reaetions, solid eatalyst-gas phase reaetions and produets, and reaetions between two immiseible liquids. Catalytie reaetions as illustrated in Chapter 1 involve a eomponent or speeies that par-tieipates in various elementary reaetion steps, but does not appear in the overall reaetion. In heterogeneous systems, mass is transferred aeross the phase. 

There are several ways of defining the rate for heterogeneous systems. In solid eatalyzed gaseous reaetions, the rate ean be defined in several ways ... 

In heterogeneous systems AP must be critically reviewed, especially if the reaction involves a two-phase mixture of liquid and gas, or if the gas flows through a deep bed of catalyst particles as in the FCC systems. AP should be checked early in the design process to assess its influence on the overall plant integrity. 

Chemical reactions obey the rules of chemical kinetics (see Chapter 2) and chemical thermodynamics, if they occur slowly and do not exhibit a significant heat of reaction in the homogeneous system (microkinetics). Thermodynamics, as reviewed in Chapter 3, has an essential role in the scale-up of reactors. It shows the form that rate equations must take in the limiting case where a reaction has attained equilibrium. Consistency is required thermodynamically before a rate equation achieves success over tlie entire range of conversion. Generally, chemical reactions do not depend on the theory of similarity rules. However, most industrial reactions occur under heterogeneous systems (e.g., liquid/solid, gas/solid, liquid/gas, and liquid/liquid), thereby generating enormous heat of reaction. Therefore, mass and heat transfer processes (macrokinetics) that are scale-dependent often accompany the chemical reaction. The path of such chemical reactions will be... 

Bromination of di-2-thienylmethane is best achieved with a bro-mide-bromate mixture in a heterogenous system. Conventional bromination with bromine in CCU was accompanied by marked tar formation. Bromination occurs in the 5- and 5 -positions of the rings as proved by the preparation of di-(5-bromo-2-thienyl) methane... 

The outstanding feature of the preparation of 2,2 -bipyridine from pyridine under the influence of metal catalysts is the absence of isomeric bipyridines among the products. In this respect reactions using metal catalysts in a heterogeneous system differ from methods which have been used to prepare bipyridines in homogeneous sys-tems. ... 

Derbyshire, W. The Dynamics of Water in Heterogeneous Systems with Emphasis to Subzero Temperatures, in Water — a Comprehensive Treatise (ed. Franks, F.), Vol. 7, p. 368, New York, Plenum Press 1982... 

Because the expression for Kn is simpler than that for Kb it is the equilibrium constant of choice for the heterogeneous system. 

On the other hand, operations such as distilling or freezing usually tend to separate solutions into the pure substances that were the components of the solution. The nearer alike the components are, the harder it is to separate them from the solution, but even in difficult cases, a variety of methods in succession usually brings about a separation. In nature, solutions are much more common than pure substances, and heterogeneous systems are more common than solutions. When we want pure substances, we often must prepare them from solutions through successive phase changes. 

Describe two homogeneous and two heterogeneous systems that are not described in the text. 

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