Stoichiometry defined

The same principles were used to observe by spectrophotometry the initial stages of the reactions of Cr(C204) 3 3 and Cr(OH2) 4C204+ with cerium(IV). For these purposes the respective stoichiometries defined by Reactions 3 and 2 were assumed. 

Based on the foregoing analysis, stoichiometry (defined as the point at which the numbers of anions and cations equal a simple ratio based on the chemistry of the crystal) is a singular point that occurs at a very specific oxygen partial pressure. This immediately begs the question if stoichiometry is a singular point in a partial pressure domain, then why are some oxides labeled stoichiometric and others nonstoichiometric To answer the question, examine Table 6.1 in which a range of stoichiometries and chemical stability domains for a number of oxides are listed. The deviation from stoichiometry, defined by Ax, where Ax is the difference between the... 

This system describes a region, or subspace, of R" that all feasible concentrations must reside in. A feasible concentration point is hence any positive state that obeys the reaction stoichiometry defined by mass balance. The AR must also be contained within S (it may constitute a very small or very big part of the space), and thus computing S provides an upper bound wherein the AR is known to reside. 

An elementary step is a reaction written exactly as it occurs at the molecular level, and the stoichiometry defined by reaction 2.1 does not describe how the chemical transformation occurs unless it represents an elementary step. Thus an arbitrary choice of stoichiometric coefficients cannot be made for example, the dissociative adsorption of a diatomic molecule such as H2 must be written... 

The change in all the species that are reacting is determined by the specific reaction stoichiometry defined in Reaction (9.5). 

In practice, for motors, turbines or furnaces, the conditions of combustion are frequently far from those corresponding to stoichiometry and are characterized either by an excess or by an insufficiency of fuel with respect to oxygen. The composition of the fuel-air mixture is expressed by the equivalence ratio, (p, defined by the relation / 5 r)... 

If one imagine.s that the fuel is used in the liquid state in the form of droplets —as in the case of fuel injection— the specific energy of the motor fuel (SE) is expressed in kilojoules per kilogram of air utilized, under predetermined conditions of equivalence ratio (stoichiometry for example). The SE is none other than the NHY /r quotient where r represents the previously defined stoichiometric ratio. 

The chapter is organized in a spiral fashion. First, we examine how the degree of polymerization and its distribution vary with the progress of the polymerization reaction, with the latter defined both in terms of stoichiometry and time. In the first round, we consider these topics for simple reaction... 

As with other problems with stoichiometry, it is the less abundant reactant that limits the product. Accordingly, we define the extent of reaction p to be the fraction of A groups that have reacted at any point. Since A and B groups... 

Step 4 Define the System Boundaries. This depends on the nature of the unit process and individual unit operations. For example, some processes involve only mass flowthrough. An example is filtration. This unit operation involves only the physical separation of materials (e.g., particulates from air). Hence, we view the filtration equipment as a simple box on the process flow sheet, with one flow input (contaminated air) and two flow outputs (clean air and captured dust). This is an example of a system where no chemical reaction is involved. In contrast, if a chemical reaction is involved, then we must take into consideration the kinetics of the reaction, the stoichiometry of the reaction, and the by-products produced. An example is the combustion of coal in a boiler. On a process flow sheet, coal, water, and energy are the inputs to the box (the furnace), and the outputs are steam, ash, NOj, SOj, and CO2. 

Another boron sulfide, of stoichiometry BS2, can be made by heating B2S3 and sulfur to 300°C under very carefully defined conditions. It is a colourless, moisture-sensitive material with a porphine-like molecular structure, BgSig, as shown in Fig. 6.29b. An alternative route to BgSie involves the reaction of dibromotrithiadiborolane with trithiocarbonic acid in an H2S generator in dilute CS2 solution ... 

In terms of the point defect energies so defined, our stoichiometry-conserving defects have formation energies given by ... 

In Chapter 4, molarity was the concentration unit of choice in dealing with solution stoichiometry. You will recall that molarity is defined as... 

One of the most important parameters that defines the structure and stability of inorganic crystals is their stoichiometry - the quantitative relationship between the anions and the cations [134]. Oxygen and fluorine ions, O2 and F, have very similar ionic radii of 1.36 and 1.33 A, respectively. The steric similarity enables isomorphic substitution of oxygen and fluorine ions in the anionic sub-lattice as well as the combination of complex fluoride, oxyfluoride and some oxide compounds in the same system. On the other hand, tantalum or niobium, which are the central atoms in the fluoride and oxyfluoride complexes, have identical ionic radii equal to 0.66 A. Several other cations of transition metals are also sterically similar or even identical to tantalum and niobium, which allows for certain isomorphic substitutions in the cation sublattice. 

King has given another and more convenient approach.3 His method is useful not only in jump experiments but also if the reaction starts all on one side. Let us start with the system A +3 2P, imagining that the perturbation causes an instantaneous shift in [A] of So- With proper regard for stoichiometry and signs, at any point during the reaction the shift is 8, defined so as to be positive. These are the equations ... 

The number-average molecular weight of a polymer may be controlled by offsetting the stoichiometry of two dissimilar mutually reactive difunctional monomers. The polymer will have the same endgroup functionality as that of the monomer used in excess. For a generic polymer made from a difunctional monomer AA with A functional groups and an excess of difunctional monomer BB widt B functional groups, r is defined as... 

The interaction of small, well defined, rhodium clusters, Rh and Rhs, with O2 has been investigated (220) by matrix infrared, and UV-visible, spectroscopy, coupled with metal/02 concentration studies, warm-up experiments, and isotopic oxygen studies. A number of binuclear O2 complexes were identified, with stoichiometries Rh2(02)n, n = 1-4. In addition, a trinuclear species Rhs(02)m, m = 2 or 6, was identified. The infrared data for these complexes, as well as for the mononuclear complexes Rh(02)x, = 1-2 (229), are summarized in Table XI. Metal-concentration plots that led to the determination of... 

First reported by Fredenhagen in 1926 F3, F4), the graphite-alkali-metal compounds possess a relative simplicity with respect to other intercalation compounds. To the physicist, their uncomplicated structure and well defined stoichiometry permit reasonable band-structure calculations to be made S2,12) to the chemist, their identity as solid, "infinite radical-anions frequently allows their useful chemical substitution for such homogeneous, molecular-basis reductants as alkali metal-amines and aromatic radical anions N2, B5). 

A number of synthetic procedures are available (Ai2). (2) For precisely defined stoichiometries, the isobaric, two-bulb method of Herold is preferred H5, H6, H2). (2) To generate compounds suitable for organic synthesis work, graphite and alkali metal may be directly combined, and heated under inert gas (Pl, lA). (5) Electrolysis of fused melts has been reported to be effective iN2). 4) Although alkali metal -amine solutions will react with graphite, solvent molecules co-inter-calate with the alkali metal. Utilization of alkali metal-aromatic radical anion solutions suffers the same problem. 

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