Stoichiometry decomposition

Metal organic decomposition (MOD) is a synthesis technique in which metal-containing organic chemicals react with water in a nonaqueous solvent to produce a metal hydroxide or hydrous oxide, or in special cases, an anhydrous metal oxide (7). MOD techniques can also be used to prepare nonoxide powders (8,9). Powders may require calcination to obtain the desired phase. A major advantage of the MOD method is the control over purity and stoichiometry that can be achieved. Two limitations are atmosphere control (if required) and expense of the chemicals. However, the cost of metal organic chemicals is decreasing with greater use of MOD techniques. 

Some nitrate is also formed, thus the HOCl/NH stoichiometry is greater than theoretical, ie, - 1.7. This reaction, commonly called breakpoint chlorination, involves intermediate formation of unstable dichloramine and has been modeled kinetically (28). Hypobromous acid also oxidizes ammonia via the breakpoint reaction (29). The reaction is virtually quantitative in the presence of excess HOBr. In the case of chlorine, Htde or no decomposition of NH occurs until essentially complete conversion to monochloramine. In contrast, oxidation of NH commences immediately with HOBr because equihbrium concentrations of NH2Br and NHBr2 are formed initially. As a result, the typical hump in the breakpoint curve is much lower than in the case of chlorine. 

The mauve colored cobalt(II) carbonate [7542-09-8] of commerce is a basic material of indeterminate stoichiometry, (CoCO ) ( (0 )2) H20, that contains 45—47% cobalt. It is prepared by adding a hot solution of cobalt salts to a hot sodium carbonate or sodium bicarbonate solution. Precipitation from cold solutions gives a light blue unstable product. Dissolution of cobalt metal in ammonium carbonate solution followed by thermal decomposition of the solution gives a relatively dense carbonate. Basic cobalt carbonate is virtually insoluble in water, but dissolves in acids and ammonia solutions. It is used in the preparation of pigments and as a starting material in the preparation of cobalt compounds. 

A gas decomposition reaction with stoichiometry 2A —> 2B -i- C follows a second order rate law rj(mol / m s) = kC, where C is the reactant concentration in mol/m. The rate constant k varies with the reaction temperature according to the Arrhenius law ... 

Nitrogen forms binary compounds with almost all elements of the periodic table and for many elements several stoichiometries are observed, e.g. MnN, Mn Ns, Mn3N2, MniN, Mn4N and Mn tN (9.2 < jc < 25.3). Nitrides are frequently classified into 4 groups salt-like , covalent, diamond-like and metallic (or interstitial ). The remarks on p. 64 concerning the limitations of such classifications are relevant here. The two main methods of preparation are by direct reaction of the metal with Ni or NH3 (often at high temperatures) and the thermal decomposition of metal amides, e.g. ... 

At higher acidities (lower pH) decomposition is slower (ti/2 days or weeks) and the pathways are more complex. The stoichiometry, kinetics and mechanisms of several other reactions of H2N2O2 with, for example, NO and with HNO2 have also been studied. 

When the reaction is performed at relatively low temperatures that prevent strong thermal decomposition of the alkali metal carbonate, the formation of C02 will be related only to the reaction and will indicate the stoichiometry of the process. Fig 8 presents mass loss isotherms of Nb02F - M2CO3 mixtures (in which M - Li, Na, K, Rb, Cs) that were subjected to thermal treatment in air at 850°C [84, 85]. It is important to mention that parallel experiments performed without the addition of Nb02F, resulted in alkali metal carbonate mass losses that were in the same order of magnitude as the measurement errors at temperatures below 850°C. 

The main advantages of the method can be formulated as follows. First, hydrofluoric acid is not needed for the decomposition stage the amount of fluorine required for the raw material decomposition can be calculated and adjusted as closely as possible to the stoichiometry of the interaction. Since the leaching of the fluorinated material is performed with water, a significant fraction of the impurities are precipitated in the form of insoluble compounds that can be separated from the solution, hence the filtrated solution is essentially purified. There is no doubt that solutions prepared in this way can be of consistent concentrations of tantalum and niobium, independent of the initial raw material composition. 

The relative thicknesses of the fuel and the oxidizer slab are determined by the stoichiometry of the particular propellant formulation. At the surface of the oxidizer slab, the solid oxidizer is assumed to vaporize, producing the gaseous oxidizer decomposition products. At the fuel surface, a similar assumption is made. 

There is an extensive literature devoted to the preparation and structure determination of coordination compounds. Thermal analysis (Chap. 2, Sect. 4) has been widely and successfully applied in determinations [1113, 1114] of the stoichiometry and thermochemistry of the rate processes which contribute to the decompositions of these compounds. These stages may overlap and may be reversible, making non-isothermal kinetic data of dubious value (Chap. 3, Sect. 6). There is, however, a comparatively small number of detailed isothermal kinetic investigations, together with supporting microscopic and other studies, of the decomposition of coordination compounds which yields valuable mechanistic information. 

The stoichiometry of decomposition of [Ni(NH3)4](NCS)2 was dependent on the method of salt preparation [1126]. Ammonia was lost in three successive steps (—NH3, —NH3, —2 NH3) from the solution-prepared salt, but the first intermediate could not be isolated from the similar reaction of material prepared by heterogenous reaction. The difference in behaviour was ascribed to differences in perfection of the crystallites resulting from the alternative preparative methods. 

In the schemes considered to this point, even the complex ones, the products form by a limited succession of steps. In these ordinary reaction sequences the overall process is completed when the products appear from the given quantity of reactants in accord with the stoichiometry of the net reaction. The only exception encountered to this point has been the ozone decomposition reaction presented in Chapter 5, which is a chain reaction. In this chapter we shall consider the special characteristics of elementary reactions that occur in a chain sequence. 

Either Mechanism I or Mechanism II can account for the decomposition of NO2. Each consists of elementary steps, each generates a highly reactive species that undergoes further chemistry, and each accounts for the observed reaction stoichiometry. Does either mechanism represent what really happens at the molecular level Before describing how to test whether a mechanism is realistic, we must introduce some additional features of mechanisms. 

Notice that over the same period the rate of O2 formation is only half the rate of NO2 consumption. This follows from the molecular view of the mechanism and from the stoichiometry of the reaction. The rate relationship among the three species involved in NO2 decomposition is given by the following expression ... 

The net reaction for this two-step mechanism is the conversion of an O3 molecule and an oxygen atom into two O2 molecules. In this mechanism, chlorine atoms catalyze ozone decomposition. They participate in the mechanism, but they do not appear in the overall stoichiometry. Although chlorine atoms are consumed in the first step, they are regenerated in the second. The cyclical nature of this process means that each chlorine atom can catalyze the destruction of many O3 molecules. It has been estimated that each chlorine atom produced by a CFC molecule in the upper stratosphere destroys about 100,000 molecules of ozone before it is removed by other reactions such as recombination CF2 Cl -b Cl CF2 CI2... 

The scaled data matrix D is decomposed using singular value decomposition (see Bonvin and Rippin (1990), Hamer (1989), Golub and van Loan (1983)) into matrices with one containing stoichiometric information which can be processed into acceptable stoichiometry. The decomposition can be easily done by any available software packages (e.g. Dongarra etal. (1979), Press et ai, (1989)). Upon decomposing one obtains ... 

The enthalpy of decomposition is now replaced by the enthalpy of reaction to analyse the potential danger. Since the danger of a chemical reaction is usually related to a modification in its procedure, which makes it uncontrollable and causes destruction of the molecular groups, it seems to make more sense to write down the most energetic reaction possible. The risk will indicate the maximum potential danger considering the stoichiometry chosen. This approach may be... 

The charge transport and optical properties of the [Si(Pc)0]-(tos)y)n materials as y=0 -+ 0.67 are reminiscent of the [Si(Pc)0]-(BF4)y)n system, but with some noteworthy differences. Again there is an insulator-to-metal transition in the thermoelectric power near y 0.15-0.20. Beyond this doping stoichiometry, the tosylates also show a continuous evolution through a metallic phase with decreasing band-filling. However, the transition seems somewhat smoother than in the BF4 system for y)>0.40, possibly a consequence of a more disordered tosylate crystal structure. Both [Si(Pc)0]-(tos)y)n optical reflectance spectra and four-probe conductivities are also consistent with a transition to a metal at y 0.15-0.20. Repeated electrochemical cycling leads to considerably more decomposition than in the tetrafluoroborate system. 

Hinshelwood and Burk [J. Chem. Soc., 127 (1105), 1925] have studied the decomposition of ammonia over a heated platinum filament at 1138° C. The reaction stoichiometry is... 

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