Stoichiometry definition

The respiratory quotient (RQ) is often used to estimate metabolic stoichiometry. Using quasi-steady-state and by definition of RQ, develop a system of two linear equations with two unknowns by solving a matrix under the following conditions the coefficient of the matrix with yeast growth (y = 4.14), ammonia (yN = 0) and glucose (ys = 4.0), where the evolution of C02 and biosynthesis are very small (o- = 0.095). Calculate the stoichiometric coefficient for RQ =1.0 for the above biological processes ... 

In another study (Ji8), it was found that graphite does not intercalate with neat XeF2 or with solutions of XeFa in acetonitrile. However, reaction with solutions of XeF2 in AHF led to copious xenon evolution, indicating that oxidation does take place, even at room temperature. Broad-line, F- and H-NMR spectra (Ell) showed the presence of both XeF2 and HF in the product, but no definite stoichiometry could be as-... 

The fused-salt electrolysis method is not suitable for obtaining pure materials of definite stoichiometry. 

Self-assembled structures can be closed if all the potential binding sites are utilized, or open if they are not. Closed assemblies have a definite geometry and stoichiometry, while open assemblies exist as mixtures of oligomers or polymers of varying stoichiometry. In addition, the self-assembled structure can be classified as cooperative if the multiple binding interactions reinforce each other to yield enhanced stability, or trivial if the binding interactions do not cooperate in the... 

The stoichiometry of an interaction between gas molecules and preadsorbed species may thus be deduced from the modifications of the Q-6 curves for a given reactant which are produced by the presence of preadsorbed species on the solid. The results are, of course, particularly conclusive when the differential heats of adsorption of small doses of reactant are measured in a sensitive calorimeter. But, such a qualitative analysis of the calorimetric data, though very useful, does not allow definite conclusions. In the preceding example, for instance, a fraction of carbon dioxide may remain adsorbed on the solid ... 

Investigations of the equilibria obtaining in solution have provided information concerning the stoichiometry and stability of the species formed when the beryllium ion is hydrolyzed. Although the identification of the minor species can never be regarded as definitive, there is little doubt that the principal species are Be2(OH)3+ and Be3(OH)3+ in acid solutions and Be(OH)3 and Be(OH)r in strongly basic solutions. Further support for these conclusions is provided by some crystal structures. The structure of [Be3(0H)3(H20)6]... 

The operational interpretation of rA, as opposed to this verbal definition, does depend on the circumstances of the reaction.1 This is considered further in Chapter 2 as a consequence of the application of the conservation of mass to particular situations. Furthermore, rA depends on several parameters, and these are considered in Section 1.4.2. The rate with respect to any other species involved in the reacting system may be related to rA directly through reaction stoichiometry for a simple, single-phase system, or it may require additional kinetics information for a complex system. This aspect is considered in Section 1.4.4, following a preliminary discussion of the measurement of rate of reaction in Section 1.4.3. 

Attempts to define operationally the rate of reaction in terms of certain derivatives with respect to time (r) are generally unnecessarily restrictive, since they relate primarily to closed static systems, and some relate to reacting systems for which the stoichiometry must be explicitly known in the form of one chemical equation in each case. For example, a IUPAC Commission (Mils, 1988) recommends that a species-independent rate of reaction be defined by r = (l/v,V)(dn,/dO, where vt and nf are, respectively, the stoichiometric coefficient in the chemical equation corresponding to the reaction, and the number of moles of species i in volume V. However, for a flow system at steady-state, this definition is inappropriate, and a corresponding expression requires a particular application of the mass-balance equation (see Chapter 2). Similar points of view about rate have been expressed by Dixon (1970) and by Cassano (1980). 

The first column lists all the species involved (including inert species, if present). The second column lists the basis amount of each substance (in the feed, say) this is an arbitrary choice. The third column lists the change in the amount of each species from the basis or initial state to some final state in which the fractional conversion is fA. Each change is in terms of fA, based on the definition in equation 2.2-3, and takes the stoichiometry into account. The last column lists the amounts in the final state as the sum of the second and third columns. The total amount is given at the bottom of each column. 

The stoichiometry of the redox processes relevant for wastewater is important for balancing these processes. Therefore, procedures are needed for this purpose. A basic definition important for the determination of process stoichiometry is the oxidation level, OX, defined as follows an imaginary charge of an element for being stabilized in a molecule compared with a corresponding low stability of the single atom. 

As depicted in Figure 2.3, electrons are transferred from the oxidation step to the reduction step of the redox reaction. The number of electrons exchanged is the fundamental basis for establishing the stoichiometry of the redox process. This fact is crucial when establishing a mass balance, as will be done by modeling sewer processes (cf. Chapters 5 and 6). The OX value is, by definition, a key element in determination of this number. 

Each of these dissociation reactions also specifies a definite equilibrium concentration of each product at a given temperature consequently, the reactions are written as equilibrium reactions. In the calculation of the heat of reaction of low-temperature combustion experiments the products could be specified from the chemical stoichiometry but with dissociation, the specification of the product concentrations becomes much more complex and the s in the flame temperature equation [Eq. (1.11)] are as unknown as the flame temperature itself. In order to solve the equation for the n s and T2, it is apparent that one needs more than mass balance equations. The necessary equations are found in the equilibrium relationships that exist among the product composition in the equilibrium system. 

In this equation, the standard chemical potential MAgjS 6e used because the deviation of 6 from stoichiometry is much less than 1. According to the definition of the standard potential, = 0, is the standard Gibbs energy of the element in the standard state AG . Then... 

Scheme 4.7 Stoichiometry-induced partner displacement in a four-component mixture (a) equilibria considered, (b) constraints imposed, (c) mole fraction definitions, and (d) a plot of mole fraction versus guest concentration ([M ] = [N ]).

For crosscurrent flow, shown in Fig. 26.96, there will be a definite reaction plane in the solids whose angle depends solely on the stoichiometry and the relative feed rate of reactants. In practice, heat transfer characteristics may somewhat modify the angle of this plane. 

Several alternate definitions of the reaction rate are used in different texts. In our notation we will always write a chemical reaction as an equation and then define the rate of that reaction as the positive rate of change for that particular stoichiometry. Consider the reaction... 

These relations assume that there is no B or C in the feed, Cbo Cco 0- With this simple stoichiometry the definitions become simpler compared to more complex sets of reactions. 

The definitions in the previous section are simple for simple stoichiometry, but they become more comphcated for complex reaction networks. In fact, one frequently does not know the reactions or the kinetics by which reactants decompose and particular product form. The stoichiometric coefficients (the v,y) in the preceding expressions are complicated to write in general, but they are usually easy to figure out for given reaction stoichiometry. Consider the reactions... 

The diffraction data were also used to guide the selection of the best preserved e.m. images of decorated actin which were then used for a 3-D reconstruction (Amos et al., 1982). In this work, it was suggested that a myosin head interacts with two actin monomers (while still retaining a 1 1 stoichiometry), but this point has not been proved definitively. 

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