Homogeneous decomposition

Volume 1 Volume 2 Volume 3 The Practice of Kinetics The Theory of Kinetics The Formation and Decay of Excited Species Section 2. HOMOGENEOUS DECOMPOSITION AND ISOMERISATION REACTIONS... 

S. J. W. Price Decomposition of metal alkyls, aryls, carbonyls and nitrosyls, pp. 197-257 (156) see especially section 2, homogeneous decomposition of metal carbonyls, and section 3.1, homogeneous decomposition of metal alkyls and aryls (of Cu, Ag, Au). 

Section 2. homogeneous decomposition and isomerisation reactions Volume 4 Decomposition of Inorganic and Organometallic Compounds Volume 5 Decomposition and Isomerisation of Organic Compounds... 

Many years ago Wojciechowski and Laidler [15] studied the homogeneous decomposition of CH4and CjHe in the presence of NO and concluded that the stable free radical NO could abstract an H atom from a paraffin molecule. Since NO is also a stable free radical and a much stronger oxidizing agent than NO, the reaction... 

The electrochemical mechanism was rejected by Salvago and Cavallotti [26] on the basis that it does not explain several features of electroless deposition of ferrous metals it does not account for the isotopic composition of the H2 gas evolved it does not explain the effect of the various solution components on reaction rate and it does not account for the homogeneous decomposition of very active solutions or the fact that they can give deposition on insulating surfaces. These authors put forward a chemical mechanism, involving various hydrolyzed nickel species, which they claim explains the observed behavior of the system ... 

It decomposes explosively at the m.p., 98°C [1], and shows a high rate of pressure increase on exothermic decomposition [2], The heat of decomposition was determined as 1.34 kJ/g by DSC, and Taii24 was determined as 88°C by adiabatic Dewar tests, with an apparent energy of activation of 223 kJ/mol [3], When finely divided, it also shows significant dust explosion hazards, with a maximum explosion pressure of 7.75 bar, and a maximum rate of pressure rise above 680 bar/s [4], Further work on homogeneous decomposition under confinement has been reported [5],... 

The state of the metal ion is of great importance to the behavior of an electroless solution. On one hand, adequate complexation ensures a relatively stable solution with respect to precipitation of hydrolyzed metal ion species and homogeneous decomposition (plating out) on the other hand, too high a concentration of certain complexants may effectively decrease to zero the kinetics of deposition. A brief examination of metal ion complexation in the context of electroless solutions will be helpful in understanding the role of the complexant. 

Grewer, T. and O. Klais, "Pressure Rise during Homogeneous Decomposition and Deflagration," I. Chem. Eng. Symposium Series, 102 (1987). 

Experiment shows that the primary reaction in the homogeneous decomposition of nitrous oxide proceeds with stoichiometry N20 => N2 + 0.5 02 and rate equation... 

Hydrocarbons and hydrogen halides are omitted since they will be dealt with elsewhere.) The chemical properties of most of these hydrides are rather well known, but this cannot be asserted for their decomposition kinetics. Some of them are very stable (H20, HF, NH3) while others decompose easily at room temperature (TeH2, PbH4). A study of the homogeneous decomposition has only been undertaken for those elements inside the frame in the Table. The pyrolyses of the others have either been found to proceed heterogeneously or the kinetics is unknown. 

Because of its high thermal stability compared to that of other hydrides, water does not decompose extensively below 2000 °K. Thus, at one atmosphere and 2500 °K it is only dissociated to the extent of 9 %. Accordingly, it is impossible to study the homogeneous decomposition by classical methods. It is only with the shock tube technique that the rates of pyrolysis of water and heavy water have been measured. 

EXPERIMENTAL CONDITIONS AND RESULTS OF DIFFERENT WORKERS ON THE HOMOGENEOUS DECOMPOSITION OF HYDROGEN PEROXIDE... 

Shock-tube experiments on the decomposition of hydrogen sulphide have been performed but were unsuccessful because traces of oxygen and other oxidizers could not be removed from the reactant24. No data are available on the homogeneous decomposition of hydrogen polysulphides, nor have the kinetics of pyrolysis of selenium and tellurium hydrides been studied. 

The vivid interest in hydrazine as a powerful propellant has stimulated many investigations both of its thermal decomposition and of its oxidation. Although hydrazine decomposes much more readily than ammonia, the study of its homogeneous decomposition by classical means using a static system is complicated considerably by wall catalysis. Thus, other experimental techniques have had to be applied, e.g. decomposition flames, flash photolysis, studies of explosion characteristics and the shock-tube technique. 

Fig. 5. Temperature dependence of the stoichiometry coefficient v for the homogeneous decomposition of hydrazine from shock tube data. , ps2h4 = 11.6, pt = 0.7 9, Fn2h4 = 5.0, Px 1-2 , Pn2h4 = 2.2, pt = 2.5 O, Pn2h4 = 1-2, pt = 1.2 Pn2h4 = 11 Pt = 2.5 Q, Pn2h4 = 11, Pt = 5.7, Q, pm2h4 = 7.4 px = 7.5. pn2h4 = partial density of N2H4 in 10 5 mole.l-1 pt — total density at reaction conditions in 10-2 mole.l". (From Michel and Wagner28.)...

Most of our knowledge about the kinetics of the homogeneous decomposition has come from shock-tube experiments. These have been performed in several laboratories under a variety of experimental conditions. However, their results are contradictory in some respects especially with regard to activation energy and on the question of the importance of chain reactions. In some cases the experimental conditions are such that consecutive reactions have to be taken into account or at least cannot be safely excluded. Until recently, one reason for the difficulty of reconciling the results of different investigators was that, if they were interpreted in terms of the unimolecular reaction48... 

The slow, thermal decomposition of hydrazoic acid in a static system has been studied by Meyer and Schumacher58. It turned out to be completely governed by heterogeneous catalysis. There are no studies on the kinetics of the homogeneous decomposition of this substance save for the investigation of its decomposition flame59. From the variation of flame properties with pressure it can be deduced that second-order reactions control the over-all rate. The unimolecular reaction... 

The kinetics of the thermally induced homogeneous decomposition of phosphine (PH3) have not yet been studied. The species PH2, PH and P2 are formed on flash photolysis of PH3 and could be identified by their absorption spectra63. There are proposals as to the mechanism of the consecutive process after the photochemical primary step, but nothing is known about the kinetic parameters of these reactions. With arsine and antimony hydride only the heterogeneous decomposition has been studied64,65. 

Tamaru et al. proposed that the homogeneous decomposition involves the initial step... 

This survey has shown that the homogeneous decomposition of hydrides of the elements becomes more complex when moving from right to left in the main... 

Because of its relevance to the chemistry of air at elevated temperatures the homogeneous decomposition of nitric oxide has received considerable attention from gas kineticists. References to early studies are given in the more recent work discussed below. The mechanisms for the decomposition and for the reverse reaction, the formation of NO from air, are well established and good quantitative data (Table 12) are available for the rate coefficients of the elementary steps. 

In spite of their relevance to air pollution and to the combustion of sulphur-contaminated fuels, kinetic data for the homogeneous decomposition of S03 are practically non-existent. The thermal decomposition is dominated by a heterogeneous component, even in clean silica vessels390 reactions of S03 at a glass surface are evident even at room temperature380. The kinetics of approach to the equilibrium... 

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