Equilibrium reactions, homogeneous

Phenomena that take place Reaction in liquid and/or vapor phase Equilibrium reactions Homogeneous or heterogeneous catalytic reactions Appearance of a second liquid phase... 

We have considered thermodynamic equilibrium in homogeneous systems. When two or more phases exist, it is necessary that the requirements for reaction equilibria (i.e., Equations (7.46)) be satisfied simultaneously with the requirements for phase equilibria (i.e., that the component fugacities be equal in each phase). We leave the treatment of chemical equilibria in multiphase systems to the specialized literature, but note that the method of false transients normally works quite well for multiphase systems. The simulation includes reaction—typically confined to one phase—and mass transfer between the phases. The governing equations are given in Chapter 11. 

Esterification is a homogeneous equilibrium reaction when all the species are liquids. The equilibrium constant value is commonly determined by following the concentration of acid with time by titration of solution aliquots with NaOH. As a homogeneous equilibrium, the concentrations of the liquids are not set to 1, but can be determined as M= moles/L of solution, assuming the liquids are ideal. 

Esterification is the first step in PET synthesis but also occurs during melt-phase polycondensation, SSP, and extrusion processes due to the significant formation of carboxyl end groups by polymer degradation. As an equilibrium reaction, esterification is always accompanied by the reverse reaction being hydrolysis. In industrial esterification reactors, esterification and transesterification proceed simultaneously, and thus a complex reaction scheme with parallel and serial equilibrium reactions has to be considered. In addition, the esterification process involves three phases, i.e. solid TPA, a homogeneous liquid phase and the gas phase. The respective phase equilibria will be discussed below in Section 3.1. 

Transesterification is the main reaction of PET polycondensation in both the melt phase and the solid state. It is the dominant reaction in the second and subsequent stages of PET production, but also occurs to a significant extent during esterification. As mentioned above, polycondensation is an equilibrium reaction and the reverse reaction is glycolysis. The temperature-dependent equilibrium constant of transesterification has already been discussed in Section 2.1. The polycondensation process in the melt phase involves a gas phase and a homogeneous liquid phase, while the SSP process involves a gas phase and two solid phases. The respective phase equilibria, which have to be considered for process modelling, will be discussed below in Section 3.1. 

According to the principles of polycondensation, all of the above reactions will also take place during SSP. The conditions for the latter, however, are different as this process is carried out at lower temperatures in a non-homogeneous environment. In order to examine the kinetics of SSP, some assumptions have to be made to simplify the analysis. These are based on the idea that the reactive end groups and the catalyst are located in the amorphous regions. Polycondensations in the solid state are equilibrium reactions but are complicated by the two-phase character of the semicrystalline polymer. 

FIA is a fixed-time analytical methodology, since neither physical equilibrium (homogenization of a portion of the flow) nor chemical equilibrium (reaction completeness) has been attained by the time the signal is detected. The operational timing must be highly reproducible, because the measurements are made under non-steady-state conditions, so that small changes may give rise to serious errors in the results obtained. 

In an equilibrium reaction, the states of reactants and products may be the same or different. If the states of reactants and products are the same, the equilibrium is called a homogeneous equilibrium. If they are different, then it is called a heterogeneous equilibrium. 

The heterogeneities of the protosolar nebula are considered as very significant by some authors I7), and as quantitatively not important by others 9). Nevertheless, it remains a fact that the model of a homogeneous accretion disc where equilibrium reaction takes place has now been replaced by a much more subtle description where a lack of homogeneity and equilibrium are facts that must be taken into account. This problem will be discussed below. 

In Fig. 4 we show first the rate curves obtained wiien only one of the two size fractions is present in the solution. In this case the isotopic exchange is fairly rapid for both size fractions. After about 1000 s the equilibrium reaction is to more than 90% completed the smaller particles, of course, react somewhat faster. The rate curves for the corresponding solution phase and the ion exchanger when presented in fractional attainment terms, U(t), are in this case (homogeneous mixture) identical and not given separately. To obtain the rate coefficients R of the two size fractions from these rate curves with Eq. (34), use is made of Eq. (32) for the case n = 1, and of Eq. (24) for the initial conditions as described (isotopic exchange D /Dg = 1 Ug = 1 R = R)... 

Define the following expressions empirical method, metastable equilibrium, kindling temperature, thermostat, interface, dynamic steady state, unimolecular reaction, bimolecular reaction, homogeneous reaction, heterogeneous reaction. 

You have been given the equation for the reaction, which provides the information needed to write the equilibrium constant expression. The equilibrium is homogeneous because the reactants and product are in the same physical state. The form of the equilibrium constant... 

Peracetic acid is the most widely used organic peroxy acid. It is a strong oxidizer, which could he used in disinfection and bleaching agent. Peracetic acid can be synthesized from acetic acid and hydrogen peroxide. The formation of peracetic acid takes place in the equilibrium reaction (1). In order to accelerate the reaction rate, acid catalyst is needed (Swem, D., 1970). Conventionally homogeneous sulphuric acid catalyst is used. The reaction scheme is shown in Eq. (1)... 

Conventionally peracetic acid is produced in a tank reactor in the presence of homogeneous acid catalyst. In the process, sulfuric acid catalyst is first charged into the reactor, after which acetic acid and hydrogen peroxide are fed into the reactor. The mixture is heated up and equilibrium reaction (1) takes place. When homogeneous acid catalyst is used, separation of it from equilibrium mixture is carried out in a distillation column. When equilibrium is reached, sub-atmospheric pressure is drawn in the reactor. Vaporization of the reaction mixture begins. In the distillation column acetic acid, hydrogen peroxide and peracetic acid are separated from sulphuric acid catalyst (Swem, D., 1970). The simplified scheme of the conventional process is illustrated in Figure 3. 

Several key questions must be answered initially in a study of reaction chemistry. First, is the reaction sufficiently fast and reversible so that it can be regarded as chemical-equilibrium controlled Second, is the reaction homogeneous (occurring wholly within a gas or liquid phase) or heterogeneous (involving reactants or products in a gas and a liquid, or liquid and a solid phase) Slow reversible, irreversible, and heterogeneous (often slow) reactions are those most likely to require interpretation using kinetic models. Third, is there a useful volume of the water-rock system in which chemical equilibrium can be assumed to have been attained for many possible reactions This may be called the local equilibrium assumption. 

The extent to which reversible reactions proceed toward products before reaching equilibrium can be described with an equilibrium constant, which is derived from the ratio of the concentrations of products to the concentrations of reactants at equilibrium. For homogeneous equilibria, the concentrations of all reactants and products can be described in moles per liter, and the concentration of each is raised to a power equal to its coefficient in a balanced equation for the reaction. The following shows the general form for the equilibrium constant expression ... 

Chemical Equilibrium in Homogeneous Gaseous Systems.—Let us consider the equilibrium of the reaction... 

The earliest method of esterifying amino acids was developed by Fischer (5). By continuously passing hydrogen chloride gas into ethanolic suspensions of amino acids, the amino acids dissolve and the solution becomes homogeneous. After adding base to the reaction mixture, the resulting ester hydrochlorides can be isolated and extracted with ether. In principle, this is not a very efficient method since it is an equilibrium reaction. However, it can be made useful by... 

This classification is important not only for kinetics and for the equilibrium of the heterogeneous catalytic reactions with a doublet mechanism, but for the equilibrium of homogeneous catalytic and non-catalytic reactions as well, because the equilibrium does not depend on the mechanism of the reaction. It is interesting to note that the cyclic activated 4- and 6-complexes, postulated by Syrkin 355), are nothing but doublet and triplet index groups, and consequently the multiplet classification must be proper for them as well hence it can also be applied to the kinetics of catalytic reactions that are not heterogeneous. 

What is a homogeneous equilibrium system Give an example of a homogeneous equilibrium reaction. What is a heterogeneous equilibrium system Write two chemical equations that represent heterogeneous equilibria. 

Expressions for homogeneous equilibria Gaseous hydrogen iodide is produced by the equilibrium reaction of hydrogen gas with iodine. Iodine and some of its compounds have important uses in medicine, as illustrated in Figure 17.7. How would you write the equilibrium constant expression for this reaction in which hydrogen and iodine react to form hydrogen iodide ... 

In this chapter we apply the general criteria for equilibrium developed in Chap. 6 to systems in which chemical reactions may occur. In Sec. 8-1, we present a general discussion of chemical equilibrium in homogeneous and heterogeneous systems. The concept of a progress variable is introduced, and the conditions for chemical equilibrium are derived. The equilibrium constant is defined, and some of its properties are developed. A discussion of the Le Chatelier-Braun principle applied to chemical reactions is presented. In Sec. 8-2, the results of Sec. 8-1 are applied to chemical reactions in mixtures of real gases. 

Mechanical extension of the generally accepted concepts of the absence of equilibrium in homogeneous gaseous reactions, in particular, in monomolec-ular reactions in the low-pressure field [27], to the kinetics of heterogeneous reactions. 

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