Unit reaction, definition

In ambivalent unit reactions like equation (4), the electron pairs are passed around an odd-membered ring from an ambivalent (redox) atom (designated by X) with one unshared pair on that atom to a form with two bonds and no unshared pair on that atom. The unit reaction definition is expanded to include ambivalent reactions with this unit change at atom X (only) of one pair for two bonds the ambivalent atom X is oxidized to accept two bonds in exchange for its unshared pair. 

PFR and CSTR in PRO/II can work for liquid and vapor phases only consequently, it must be declared that all components involved in the reaction are vapor and liquid phases (solid should be excluded). After selecting component click on Components Phases, and change the components phase to liquid and vapor only. From the Thermodynamic Data select BWRS which is the most suitable thermodynamic fluid package for such components. Build the PFR process flow sheet and specify inlet stream conditions (760°C, 162 kPa). The inlet mass flow rate of acetone is 7.85 kg/h. Under the Input menu, select Reaction Data, use the power law, and enter stoichiometric coefficients. Double click on the reactor in the PFD area and select the reaction set name. Click on Unit Reaction Definitions and specify the kinetic data as shown in Figure 5.21. Press Reactor Data, indicate 6.366 m for length and 1 m for the diameter (total volume of 5 m ). The process flow sheet and stream table properties are exposed in Figure 5.22. 

A catalytic process is commercially viable if the catalyst transformation is achieved within definite, practical limits of space and time. To quantify this aspect, one can determine the so-called space-time yield. This measure of activity is simply the amount of product obtained per unit time and per unit reaction space (where reaction space is usually the reactor volume). Weisz (79) pointed out that in industry the useful space-time yield is rarely less than 10"6 g/mol of reactant per cubic centimeter of volume of reactor space per second. This has been called the Weisz window on reality. Figure 9 (79) shows the Weisz window and other windows of chemical activity that apply to biochemistry and petroleum geochemistry (79). 

The rate along the basic route N(p) is denoted as runit time per unit reaction space. Here v p) is the stoichiometric... 

Enzyme activity is expressed in units of activity. The Enzyme Commission of the International Union of Biochemistry recommends to express it in international units (lU), defining 1 lU as the amount of an enzyme that catalyzes the transformation of 1 pmol of substrate per minute under standard conditions of temperature, optimal pH, and optimal substrate concentration (International Union of Biochemistry). Later on, in 1972, the Commission on Biochemical Nomenclature recommended that, in order to adhere to SI units, reaction rates should be expressed in moles per second and the katal was proposed as the new unit of enzyme activity, defining it as the catalytic activity that will raise the rate of reaction by 1 mol/second in a specified assay system (Anonymous 1979). This latter definition, although recommended, has some practical drawbacks. The magnitude of the katal is so big that usual enzyme activities expressed in katals are extremely small numbers that are hard to appreciate the definition, on the other hand, is rather vague with respect to the conditions in which the assay should be performed. In practice, even though in some journals the use of the katal is mandatory, there is reluctance to use it and the former lU is still more widely used. 

While the notation is by definition one for unit reactions, the system allows a number of composite reactions, of two unit reactions in succession, implicit in the initial enolization of the carbonyl, followed by the construction reaction of the... 

The intellectual models for such classification were summarized and compared first. These start with the explicit or implicit definition of the basic or unit reaction to be classified, excluding schemes of sequential reactions even though in the laboratory several reactions, however defined, may occur in one operation. 

These observations suggest how the terminal mechanism can be proved to apply to a copolymerization reaction if experiments exist which permit the number of sequences of a particular length to be determined. If this is possible, we should count the number of Mi s (this is given by the copolymer composition) and the number of Mi Mi and Mi Mi Mi sequences. Specified sequences, of any definite composition, of two units are called dyads those of three units, triads those of four units, tetrads those of five units, pentads and so on. Next we examine the ratio NmjMi/Nmi nd NmjMiMi/NmiMi If these are the same, then the mechanism is shown to have terminal control if not, it may be penultimate control. To prove the penultimate model it would also be necessary to count the number of Mi tetrads. If the tetrad/triad ratio were the same as the triad/dyad ratio, the penultimate model is proved. 

Before discussing such theories, it is appropriate to refer to features of the reaction rate coefficient, k. As pointed out in Sect. 3, this may be a compound term containing contributions from both nucleation and growth processes. Furthermore, alternative definitions may be possible, illustrated, for example, by reference to the power law a1/n = kt or a = k tn so that k = A exp(-E/RT) or k = n nAn exp(—nE/RT). Measured magnitudes of A and E will depend, therefore, on the form of rate expression used to find k. However, provided k values are expressed in the same units, the magnitude of the measured value of E is relatively insensitive to the particular rate expression used to determine those rate coefficients. In the integral forms of equations listed in Table 5, units are all (time) 1. Alternative definitions of the type... 

Biochemistry can be defined as the science concerned with the chemical basis of life (Gk bios life ). The cell is the structural unit of living systems. Thus, biochemistry can also be described as the science concerned with the chemical constituents of living cells and with the reactions and processes they undergo. By this definition, biochemistry encompasses large areas of cell biology, of molecular biology, and of molecular genetics. 

Representative condensation polymers are listed in Table I. The list is by no means exhaustive, but it serves to indicate the variety of condensation reactions which may be employed in the synthesis of polymers. Cellulose and proteins, although their syntheses have not been accomplished by condensation polymerization in the laboratory, nevertheless are included within the definition of condensation polymers on the ground that they can be degraded, hydrolytically, to monomers differing from the structural units by the addition of the elements of a molecule of water. This is denoted by the direction of the arrows in the table, indicating depolymerization. 

The degree of branching by transfer with polymer obviously will increase with the conversion since the relative incidence of branching must depend on the ratio of polymer to monomer in the system. To examine the matter from the point of view of reaction rates, let 6 represent the fraction of monomer molecules which have polymerized out of a total of iVo in the system, and let v represent the total number of branches. (At variance with the definition used elsewhere. No is the total number of units polymerized and unpolymerized as well.) The rates of generation of branches and of polymerization can then be written... 

It is important to appreciate the fact that when two or more reaction rates are to be compared and/or combined, they should be defined in the same manner. For instance, if it is required to combine a mass transfer step and a reaction step, then the rates corresponding to both should be defined in an identical manner. Since the mass transfer rate by definition is the flow of material per unit time normal to a unit surface... 

It is very often necessary to characterize the redox properties of a given system with unknown activity coefficients in a state far from standard conditions. For this purpose, formal (solution with unit concentrations of all the species appearing in the Nernst equation its value depends on the overall composition of the solution. If the solution also contains additional species that do not appear in the Nernst equation (indifferent electrolyte, buffer components, etc.), their concentrations must be precisely specified in the formal potential data. The formal potential, denoted as E0, is best characterized by an expression in parentheses, giving both the half-cell reaction and the composition of the medium, for example E0,(Zn2+ + 2e = Zn, 10-3M H2S04). 

Summary. In summary, when modeling with the fugacity concept, all equilibria can be treated by Z values (one for each compartment) and all reaction, advection and transport processes can be treated by D values. The only other quantities requiring definition are compartment volumes and emission rates or initial concentrations. A major advantage is that since all D quantities are in equivalent units they can be compared directly and the dominant processes identified. By converting diverse processes such as volatilization, sediment deposition, fish uptake and stream flow into identical units, their relative importance can be established directly and easily. Further, algebraic manipulation... 

In this case one obtains an expression for that cannot be manipulated to yield a simple algebraic form. However, if the concentration of one species is known as a function of time, the concentrations of all other species may be determined from the definition of the extent of reaction per unit volume that is,... 

In order to have a finite probability that termolecular collisions can occur, we must relax our definition of a collision. We will assume that the approach of rigid spheres to within a distance of one another constitutes a termolecular collision that can lead to reaction if appropriate energy and geometry requirements are met. This approach is often attributed to Tolman (41). The number of ternary collisions per unit volume per unit time between molecules A, B, and C such that A and C are both within a distance of B is given by ZABC. 

Angstrom units, definition, 128 Anthracene, carcinogenic activity, 45 Anthracenedihydrodiols, synthesis, 45 Arylnitrones, reaction mechanism, 363f... 

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