ELEMENTARY GAS PHASE REACTIONS

The modem approach to revealing the mechanisms of complex chemical reactions is based on the achievements of computer technique. Computer methods make it possible to calculate different variants of chemical mechanisms and reveal key elementary reactions, which are needed to be experimentally studied. Therefore, the experimental chemical kinetics in the gas phase concentrated its attention on studying elementary reactions. Fundamental problems of the chemical kinetics associated with the development of concqits about the physics of the elementary chemical act also lie in this area. Below we present the modem experimental methods and theoretical approaches for studying elementary reactions. 

Both heavy (atoms, ions, molecules) and light (electrons, photons) particles can be involved in collisions. Polyatomic molecules have internal degrees of freedom (vibrational and rotational motion of atoms) and, in this sense, they have an internal structure. 

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The foundations of the modem tireory of elementary gas-phase reactions lie in the time-dependent molecular quantum dynamics and molecular scattering theory, which provides the link between time-dependent quantum dynamics and chemical kinetics (see also chapter A3.11). A brief outline of the steps hr the development is as follows [27],... 

The simplest theories of reactions on surfaces also predict surface rate laws in which the rate is proportional to the amount of each adsorbed reactant raised to the power of its stoichiometric coefficient, just like elementary gas-phase reactions. For example, the rate of reaction of adsorbed carbon monoxide and hydrogen atoms on a metal surface to produce a formyl species and an open site,... 

This problem is an extension of problems 7-10 and 7-11 on the dehydrogenation of ethane to produce ethylene. It can be treated as an open-ended, more realistic exercise in reaction mechanism investigation. The choice of reaction steps to include, and many aspects of elementary gas-phase reactions discussed in Chapter 6 (including energy transfer) are significant to this important industrial reaction. Solution of the problem requires access to a computer software package which can handle a moderately stiff set of simultaneous differential equations. E-Z Solve may be used for this purpose. 

Hydroxyl and Oxygen Atoms, Mechanisms and Rate Constants of Elementary Gas Phase Reactions Involving (Avramenko and... 

The importance of distinguishing between elementary and overall reactions comes in formulating rate laws. For elementary reactions only, the rate law may be written directly from the stoichiometric equation. Thus for the general elementary gas-phase reaction... 

Develop a boundary-layer model of the process, using an elementary gas-phase reaction mechanism H202Mech.txt but neglecting heterogeneous chemistry at the surface. Simulate the process over a range of potential process pressures. 

We begin by establishing the relation between the so-called reaction cross-section bimolecular rate constant. Let us consider an elementary gas-phase reaction,... 

When we have expressed k(T) in terms of microscopic information, we can obtain a corresponding microscopic interpretation of the activation energy. It should be stressed that the following relations are only valid for elementary gas-phase reactions. 

A brief sketch of what we know about the kinetics of RDX decomposition is needed for context for the discussion of the simulation studies. In most experiments the data are taken with little experimental control, with the observations complicated by the rapid release of large amounts of energy, and with the liquid or solid undergoing phase transitions and chemical reactions to form small gaseous molecules such as N2O, H20, H2CO, HCN, NO, N02, CO, and C02. The reaction mechanisms involve many sequential, branched pathways, which are strongly dependent on the experimental conditions. It is not our purpose here to try to sort out the mechanisms for the various conditions, but we do need, for foundation, to discuss the experimental observations relevant to the elementary gas-phase reactions. 

Consider the reversible, elementary, gas phase reaction shown below that occurs at 300 K in a constant volume reactor of 1.0 L. 

As an extension of Exercise 15, consider the reversible, elementary, gas phase reaction of A and B to form C occurring at 300 K in a variable volume (constant pressure) reactor with an initial volume of 1.0 L. For a reactant charge to the reactor of 1.0 mol of A, 2.0 mol of B, and no C, find the equilibrium conversion of A. Plot the composition in the reactor and the reactor volume as a function of time. 

Another engineer suggests that instead of changing catalyst size it would be better to pack the catalyst in a shorter reactor with twice the pipe diameter. If all other conditions remain the same, is this suggestion better The elementary gas-phase reaction... 

P13-13b a decaying catalyst is fed to a fluidized CSTR at a rate of 20 kg/s. The I-m- CSTR contains 200 kg of catalyst. The catalyst decay follows second-order kineties. The elementary gas-phase reaction... 

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