Thermodynamics and Kinetics of Transformation Reactions

Illustrative Example 12.1 Energetics ofSyntrophic Cooperation in Methanogenic Degradation 

Illustrative Example 12.2 Transformation of Methyl Bromide to Methyl Chloride and Vice Versa 

Phenomenological Description of Reaction Kinetics First-Order Kinetics 

The First-Order Linear Inhomogeneous Differential Equation (FOLIDE) First-Order Reaction Including Back Reaction Reaction of Higher Order Catalyzed Reactions 

Box 12.2 An Enzyme-Catalyzed Reaction (Michaelis-Menten Enzyme Kinetics) 

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Any chemical transformation that implies the transfer of charge across the interface between an electronic conductor (the electrode) and an ionic conductor (the electrolyte) is referred to as an electrochemical reaction. An electrochemical reaction can include one or several electrode reactions. For example the reaction (1.3) is an electrochemical reaction each atom of iron that passes into solution implies the exchange of two electrons between the metal and the protons. Two electrode reactions are involved the oxidation of the iron and the reduction of the proton. According to the definition given above, all corrosion reactions that involve metal oxidation are electrochemical reactions. In order to understand and control corrosion phenomena it is essential to study the thermodynamics and kinetics of electrochemical reactions. 

In spite of all our knowledge of the structure of enzymes and the thermodynamics and kinetics of enzyme-catalyzed reactions, we are still far from an adequate understanding of the enzymic mechanism of action. In modem organic chemistry reactions are explained on the basis of the electron theory and the chemical bond. In principle, this explanation should also apply to enzymic transformations, but so far it has been possible only in a few instances to arrive at the detailed reaction mechanism. 

Chromik, R.R. Cotts, E.J. A Study of the kinetics and energetics of solid state reactions in Pd/Sn diffusion couples, thermodynamics and kinetics of phase transformations. Proceedings Fall Meeting of the Materials Research Society, Pittsburgh, PA, 1995 307 pp. 

Steinreiber, J., Schurmann, M., Wolberg, M. et al. (2007) Overcoming thermodynamic and kinetic limitations of aldolase-catalyzed reactions by applying multienzymatic dynamic kinetic asymmetric transformations. Ange-wandte Chemie International Edition. 46, 1624-1626. 

The energy storage and power characteristics of electrochemical energy conversion systems follow directly from the thermodynamic and kinetic formulations for chemical reactions as adapted to electrochemical reactions. First, the basic thermodynamic considerations are treated. The basic thermodynamic equations for a reversible electrochemical transformation are given as... 

The field of theoretical molecular sciences ranges from fundamental physical questions relevant to the molecular concept, through the statics and dynamics of isolated molecules, aggregates and materials, molecular properties and interactions, and the role of molecules in the biological sciences. Therefore, it involves the physical basis for geometric and electronic structure, states of aggregation, physical and chemical transformations, thermodynamic and kinetic properties, as well as unusual properties such as extreme flexibility or strong relativistic or quantum-field effects, extreme conditions such as intense radiation fields or interaction with the continuum, and the specificity ofbiochemical reactions. 

In Chapter 8, we addressed proton transfer reactions, which we have assumed to occur at much higher rates as compared to all other processes. So in this case we always considered equilibrium to be established instantaneously. For the reactions discussed in the following chapters, however, this assumption does not generally hold, since we are dealing with reactions that occur at much slower rates. Hence, our major focus will not be on thermodynamic, but rather on kinetic aspects of transformation reactions of organic chemicals. In Section 12.3 we will therefore discuss the mathematical framework that we need to describe zero-, first- and second-order reactions. We will also show how to solve somewhat more complicated problems such as enzyme kinetics. 

In Chapter 3 we described the structure of interfaces and in the previous section we described their thermodynamic properties. In the following, we will discuss the kinetics of interfaces. However, kinetic effects due to interface energies (eg., Ostwald ripening) are treated in Chapter 12 on phase transformations, whereas Chapter 14 is devoted to the influence of elasticity on the kinetics. As such, we will concentrate here on the basic kinetics of interface reactions. Stationary, immobile phase boundaries in solids (e.g., A/B, A/AX, AX/AY, etc.) may be compared to two-phase heterogeneous systems of which one phase is a liquid. Their kinetics have been extensively studied in electrochemistry and we shall make use of the concepts developed in that subject. For electrodes in dynamic equilibrium, we know that charged atomic particles are continuously crossing the boundary in both directions. This transfer is thermally activated. At the stationary equilibrium boundary, the opposite fluxes of both electrons and ions are necessarily equal. Figure 10-7 shows this situation schematically for two different crystals bounded by the (b) interface. This was already presented in Section 4.5 and we continue that preliminary discussion now in more detail. 

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