Bulk chemical reactions

In bulk chemical reactions, an oxidizer (electron acceptor) and fuel (electron donor) react to form products resulting in direct electron transfer and the release or absorption of energy as heat. By special arrangements of reactants in devices called batteries, it is possible to control the rate of reaction and to accomplish the direct release of chemical energy in the form of electricity on demand without intermediate processes. 

Batteries are miniatuie chemical leactois that convert chemical energy into electrical energy on demand. The thermodynamics of battery systems foUow direcdy from that for bulk chemical reactions (10). For the general reaction... 

The Van t Hoff isotherm identifies the free energy relationship for bulk chemical reactions. 

Activation Processes. To be useful ia battery appHcations reactions must occur at a reasonable rate. The rate or abiUty of battery electrodes to produce current is determiaed by the kinetic processes of electrode operations, not by thermodynamics, which describes the characteristics of reactions at equihbrium when the forward and reverse reaction rates are equal. Electrochemical reaction kinetics (31—35) foUow the same general considerations as those of bulk chemical reactions. Two differences are a potential drop that exists between the electrode and the solution because of the electrical double layer at the electrode iaterface and the reaction that occurs at iaterfaces that are two-dimensional rather than ia the three-dimensional bulk. 

In this chapter, we present most of the equations that apply to the systems and processes to be dealt with later. Most of these are expressed as equations of concentration dynamics, that is, concentration of one or more solution species as a function of time, as well as other variables, in the form of differential equations. Fundamentally, these are transport (diffusion-, convection-and migration-) equations but may be complicated by chemical processes occurring heterogeneously (i.e. at the electrode surface - electrochemical reaction) or homogeneously (in the solution bulk chemical reaction). The transport components are all included in the general Nernst-Planck equation (see also Bard and Faulkner 2001) for the flux Jj of species j... 

Surface or bulk chemical reactions, including erosion and degradation are important aspects of polymeric systems. These processes can be desired, as is the case for surface modification reactions to increase, e.g., biocompatibility or drug delivery applications, while other processes are unwanted, such as ageing, degradation in harsh environments, or erosion. AFM approaches offer a unique possibility to study these processes in many cases under realistic conditions and thereby help identify the underlying mechanisms. 

In this chapter we will first discuss briefly the basic theory behind ab nitio methods. Then a discussion of transition state theory, in light of the ab initio capabilities, will be taken up. This discussion will be followed by an analysis of the molecular mechanisms in water-silicate reactions and the ab initio elucidation of the adsorption and kinetic barriers involved in the bulk chemical reactions occurring at mineral-water interfaces. 

In reactions involving gas-liquid mixing, one of the first things to determine is the controlling process (bulk) chemical reaction or mass transfer. Experimentally, this is done by checking the effect of agitator speed on rate of reaction, as shown in Figure 9.22. 

Table 5.2 Heat of formations (single bond dissociation en-ergy), A H2, corresponding to different metal fluorides [97] are shown. Based on a bulk chemical reaction of M, + M2F — ...

The gas-liquid equilibrium is given by Henry s law (Chapter 4.3.2). In the case of surface and/or bulk chemical reactions the flux equation (mass budget) is expressed by ... 

Locale of the extraction reaction interfacial vs. aqueous bulk chemical reaction... 

Thermosets are network-forming polymers. Unlike thermoplastic polymers, whose processing requires only physical changes such as melting, thermosets are distinguished by the bulk chemical reactions that are involved in their use. 

In the case of chlorine, the mechanism of poisoning does not proceed by a surface chemisorption reaction but by a bulk chemical reaction with the potassium promoter. A similar calculation to that shown above, but with respect to the maximum chlorine content, may also be carried out. Let us assume that the catalyst has a potassium content of 1 wt%. 

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