Chemical reactions in gas phase

A reaction path that was first proposed by Fukui [30] has been successfully used to describe chemical reactions in gas phases. In this method, chemical... 

There exists now an enormous literature on the applications of the classical or semiclassical collision and transition state theories to different types of chemical reactions in gas phase and in solution (see,for instance, /1,3,19a,35f49/). For our purposes it is sufficient to show the applicability of the general formulations presented in Chapter III to some simple gas phase and dense phase reactions. In this way we would like to demonstrate, first, the computational possibility of these formulations, and, second, their utility for an understanding of the influence of various factors, such as nonseparability effects, quantum effects, isotope effects a.o. on the kinetic parameters. 

Quite a few Car-Parrinello simulations have been performed so far to characterize various chemical reactions in gas phase,s s -... 

The rate expressions for surface processes thus take the same form as well-known expressions for chemical reactions in gas phase or in solution. Whereas the activities of gas- or liquid-phase reactants are expressed as pressures or concentrations, the activities of surface reactants are expressed in terms of the fractional coverages of adsorbates and of free sites. For surface processes, we can define reaction fractions by taking the product of the activities of the left-hand side of a reaction equation and dividing it by the right-hand side. For example, with the adsorption-desorption reaction given by... 

Thus, we considered a number of examples of application of the sensor technique in experiments on heterogeneous recombination of active particles, pyrolysis and photolysis of chemical compounds in gas phase and on the surface of solids, such as oxides of metals and glasses. The above examples prove that, in a number of cases, compact detectors of free atoms and radicals allow one to reveal essential elements of the mechanisms of the processes under consideration. Moreover, this technique provides new experimental data, which cannot be obtained by other methods. Sensors can be used for investigations in both gas phase and adsorbed layers. This technique can also be used for studying several types of active particles. It allows one to determine specific features of distribution of the active particles along the reaction vessel. The above experiments demonstrate inhomogeneity of the reaction mixture for the specified processes and, consequently, inhomogeneity of the... 

The interaction of an electron with a surface produces at least three phenomena which are important in a plasma environment. They are (1) chemical reactions between gas phase species and a surface where electron bombardment is required to activate the process, (2) electron-induced secondary-electron emission, and (3) electron-induced dissociation of sorbed molecules. A fourth phenomenon — lattice damage produced by energetic electrons — depends sensitively upon the properties of the material being bombarded, and, it is important in specialized situations, but it will not be discussed in this paper. 

The development of new models for the prediction of chemical effects in the environment has improved. An Eulerian photochemical air quality model for the prediction of the atmospheric transport and chemical reactions of gas-phase toxic organic air pollutants has been published. The organic compounds were drawn from a list of 189 species selected for control as hazardous air pollutants in the Clean Air Act Amendments of 1990. The species considered include benzene, various alkylbenzenes, phenol, cresols, 1,3-butadiene, acrolein, formaldehyde, acetaldehyde, and perchloroethyl-ene, among others. The finding that photochemical production can be a major contributor to the total concentrations of some toxic organic species implies that control programs for those species must consider more than just direct emissions (Harley and Cass, 1994). This further corroborates the present weakness in many atmospheric models. 

Experimental studies aimed at detection of chemical conjugation in gas-phase oxidation reactions with hydrogen peroxide [31, 37] were performed in a flow system, in an integral reactor (the plug flow), which construction provided for H202 injection to the reaction zone. 

Absorption and fluorescence spectra of molecules in solution are broadened, in general, compared with those in gas phase because the energy of the molecule dissolved in solvent is fluctuating due to the orientational fluctuation of the surrounding solvent molecules. The fluctuational motion of the solvent plays an important role in chemical reactions in solution phase such as an electron transfer reaction, for example, where the energy fluctuation of the reactants caused by the solvent fluctuation is considered to be essential to realize the transition state of the reaction. 

R.W. Walker, A Critical Survey of Rate Constants for Reactions in Gas-Phase Hydrocarbon Oxidation, Specialist Periodical Reports (The Chemical Society, London (1975) p. 161. 

It should be noted that the overall electrochemical process can involve coupled chemical reactions in solution phase or involve gas evolution and/or deposition of solids and/or formation of adsorbates onto the electrode surface, so that electrochemical processes can, in general, be regarded as multistep reaction processes. As far as electrochemical responses are strongly conditioned, not only by the kinetics of... 

The SiC coating was composed of two layers a thin SiC conversion layer (several pm) and a thick CVD coating layer. The conversion layer was formed by chemical reaction of gas phase Si with carbon in the substrate. The gaseous Si was provided by thermal decomposition of bubled SiCl, in which carrier gas was H,. The aim of the conversion layer is to make bonding strength of the coating higher. The CVD layer was thermally deposited at three kinds of temperatures, 1800, 1600 and 1200"C, named hereafter CVD-18, -16 and -12, respectively. 

The descriptions of molecular dynamics and the theory of chemical reactions in gas and condensed phases are based on the concept of potential energy function (hypersurface) [1,2] rooted in the Bom-Oppenheimer (BO) approach [3]. The parametric dependance of the electronic wave function with respect to nuclear coordinates is the basic idea on which the BO framework rest. In this paper, a different approach is taken. The electronic state functions are taken to be independent from the instantaneous nuclear positions. As a first step, we consider molecular systems which are characterized by stationary nuclear configurations belonging to particular symmetry groups. The corresponding electronic stationary states must always transform according to given irreduci-... 

In spite of the topochemical principle, the details of solid-state reactions may be difficult to understand. Whai we think of chemical reactions in solution or in the gas phase, we normally focus attention on the fate of a single molecule and its interaction with one or two immediate neighbors. This kind of simplification is generally not possible when we deal with phase transitions or solid-solid chemical reactions in which phase separation occurs. Even when overall crystal orientation is maintained between initial and final... 

Reactions in condensed media (liquids and solids are in general much more complicated than reactions in gas phases. In some cases the diffusion of reactants or products, which requires a low activation energy (4-5 kcal/mole), may be the rate-limiting step. For most reactions in solution, however, the proper chemical interaction, for which a higher activation energy (10-20 kcal/mole) is necessary, limits the reaction rate. We are interested here only in the theory of reactions of this kind. 

Similar to the liquid-liquid system, the volume-surface diameter of dispersed phase particles in a liquid-gas flow is determined by the initial size of the bubbles at the gas input points [81-83]. An increase of the liquid-gas flow rate leads to an increase of the shear deformation influence of the dispersed phase particles and therefore, to a decrease in the diameter of the gas bubbles in the input area of the device. Finally, it leads to the formation of a finely dispersed system in a device with an increase of the liquid-gas flow rate (Figure 2.23). Fast chemical reactions in two-phase gas-liquid systems usually occur in a gas-phase excess, so it is reasonable to analyse the influence of the gas content in a flow on the change of phase contact surface. 

Model Reaction in Gas Phase To confirm the results from the above calculation, the irradiation of the gas mixture of C6F14 and hydrazine with the laser was examined. After the photolysis of the mixture, the formation of HF was detected by a chemical analysis (34). It is presumed that the hydrogen radical generated by the photolysis of hydrazine abstracts the fluorine atom on the surface of a PTFE film to form HF, and that reactive species such as N-containing NH2 and N2H3 can be substituted in the C-chain after F-abstraction. 

This paper also provided much of the early stimulus for developing semiclassical and quantum mechanical theories of chemical reaction dynamics, which is a research field that continues to be active. In addition, this paper provided the foundation for molecular dynamics studies of chemical reactions in condensed phases, including applications to gas-surface scattering and bio-molecular simulation. 

In Chemical Reactions in Gas, Liquid and Solid Phases Synthesis, Properties and Application, Zaikov, G. E. Kozlowski, R. M., Eds. Nova Science Pubhshers New York, 2010. 

In order to improve our understanding of the speciation of mercuiy in FGD gypsum, the authors have used thermodynamic equilibrium models in order to predict the composition of the chemical species in gas phase using the HSC-Chemistry 5.0 software. The theoretical study was carried out in the same conditions that the experimental study, at atmospheric pressure and temperatures ranging between 25 and 800 C. HSC-Chemistiy program uses data base with enthalpy, entropy and calorific capacity values for more than 15000 species. This software allows modify the quantity of different species implicated in the reaction and the program determines tlie products formed, theoretically, in the equilibrium. 

Derivation of chemical equilibrium relationships for simple reactions Reactions in gas phase Reactions in liquid phase Explore yourself References Bibliography... 

A workable reaction mechanism must embrace all reactants, products and reaction intermediates produced and consumed in a catal3ftic reaction. In gas-phase reactions, two-molecule reaction is popular and three-molecule reaction is very less. For catalyst surfaces, multi-molecule steps become important as the concentration of chemical species is higher than that of gas-phase, and even in this case the reaction between more than three molecules is in general not common. 

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