Chemical kinetics, 536. See

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],... 

Chemical reactions obey the rules of chemical kinetics (see Chapter 2) and chemical thermodynamics, if they occur slowly and do not exhibit a significant heat of reaction in the homogeneous system (microkinetics). Thermodynamics, as reviewed in Chapter 3, has an essential role in the scale-up of reactors. It shows the form that rate equations must take in the limiting case where a reaction has attained equilibrium. Consistency is required thermodynamically before a rate equation achieves success over tlie entire range of conversion. Generally, chemical reactions do not depend on the theory of similarity rules. However, most industrial reactions occur under heterogeneous systems (e.g., liquid/solid, gas/solid, liquid/gas, and liquid/liquid), thereby generating enormous heat of reaction. Therefore, mass and heat transfer processes (macrokinetics) that are scale-dependent often accompany the chemical reaction. The path of such chemical reactions will be... 

As the text is aimed at undergraduates studying core physical chemistry, only the basics of theoretical kinetics are given, but the fundamental concepts are clearly explained. More advanced reading is given in my book Fundamental Chemical Kinetics (see reading lists). 

The principles and methods of scale-up can be applied to chemical reactors. In the absence of significant thermal effects, i.e., when the ratio <2r/ Vr may be considered negligible, ideal batch reactors do not show any problem of scale-up, because the volume Vr does not appear in the mathematical model (2.17), so that their performance is only determined by chemical kinetics (see Sect. 2.3). On the contrary, a very complex behavior is expected for real reactors in fact, this behavior cannot be analyzed in terms of mathematical models, and the design procedures must be largely based on semi-empirical rules of scale-up. 

For this simple two-state transition, the traditional deterministic chemical kinetics (see Chapter 3) is based on rate equations for the concentration of A ... 

It is useful to have a complete picture of the entire distribution of molecular speeds. This turns out to be important when we study chemical kinetics (see Chapter 18), where we will need to know what fraction of a sample of molecules has kinetic energy above the minimum necessary for a chemical reaction. In particular, we would like to know what fraction of molecules, AN/N, have speeds between u and u + Am. This fraction gives the speed distribution function f u) ... 

For further information on the mathematical treatment of chemical kinetics, see the thoughtful monograph by Erdi and Toth (1989). 

At the end of this chapter we will now briefly discuss a theoretical approach to the description of chaotic processes encountered in chemical kinetics, see Section 1.3 and Sections 6.2.2.4, 6.3.2.4. In Section 6.2.2.4 we described the method of generation and physical meaning of a chaotic state of the Belousov-Zhabotinskii reaction carried out in a flow reactor. 

We need to begin with several definitions of terms used throughout. (For an introduction to chemical kinetics see [1].)... 

A little similar but another choice of standard state, used e.g. in gas chemical kinetics, see Sect. 4.9, is the pure ideal gas at given temperature and at fixed standard molar concentration Cs (usually unit one, say c, = 1 mol/m ). Therefore, by (4.433), the standard function (/u, in (4.441)) is defined as iif(T) = 4- RTlnCj and... 

Kinetics, specifically studying rate laws and measurement of rate constants, can only be done under laboratory conditions, whereas reaction conditions should be simulated in special reactors ( smog chambers ) closely resembling the atmospheric one. Once established, the k-value of an elementary reaction is universally applicable, or in other words, pure chemistry is independent of meteorological and geographical specifics but the conditions for reactions (pressure, temperature, radiation, humidity) and the concentration field depends from location. This is the difference to air chemistry . For more detailed information on chemical kinetics, see Zumdahl (2009), Atkins (2008) and Houston (2006). 

Because A5univ is positive, we predict that the reaction is spontaneous at 25°C. It is important to keep in mind that just because a reaction is spontaneous does not mean that it will occur at an observable rate. The synthesis of ammonia is, in fact, extremely slow at room temperature. Thermodynamics can tell us whether a reaction will occur spontaneously under specific conditions, but it does not say how fast it will occur. Reaction rates are the subject of chemical kinetics (see Chapter 13). 

A combination of the two relations AlO.l and A10.2, or composition of the two paths in the Formal Graph, provides a third operator of viscous inertia which appears as a velocity constant analogous to those constants met in chemical kinetics (see the next case study All Reactive Chemical Species ), or more generally in relaxation of dynamic processes... 

For texts on Chemical Kinetics see, for example (a) Laidler, K. J. Chemical Kinetics 3rd ed. Benjamiri/Ctimmings Menlo Fhrk,... 

The probl of predicting the performance and determining the size of a reactor can be divided into two sequential steps. The first is the study of the rate at which the chemical leacticm occurs and the variables which affect this rate. This is the subject of chemical kinetics (see Chapter 4). The second is the problem of using reaction rate data to predict perfoonance and/or to detennine the size of the equipment to obtain the requited quantity and quality of product. This is the subject of f uts II and HI. 

On chaos and non-linear chemical kinetics, see Epstein and Pojman (1998), Gray and Scott (1994) Kapral and Fraser (2001), Slinko and Jaeger (1994), Kapral and Showalter (1995), Scott, (1994), Scott (1987), Noyes (1989). 

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