Coupling, of chemical reactions

Models of atmospheric phenomena are similar to those of combustion and involve the coupling of exceedingly complex chemistry and physics with three-dimensional hydrodynamics. The distribution and transport of chemicals introduced into groundwater also involve a coupling of chemical reactions and transports through porous solid media. The development of groundwater models is critical to understanding the effects of land disposal of toxic waste (see Chapter 7). 

THL.3. 1. Prigogine, Remarque sur le principe de reciprocite d Onsager et le couplage des reactions chimiques (Remarks on Onsager s reciprocity principle and the coupling of chemical reactions). Bull. Cl. Set Acad. Roy. Belg. 32, 30-35 (1946). 

Dr. Sanfeld refers to phenomena that concern membranes and surface behaviors rather than bulk solutions whether such behaviors play a role in the motion of fluids in cells remains an open question. On the other hand, the coupling of chemical and hydrodynamic effects is not a necessary condition to the existence of rotations and macroscopic transport of matter. We have seen in the lecture of Professor Prigogine that such effects can result more simply from the coupling of chemical reactions with transport phenomena like diffusion. 

What are the additional assumptions concerning the presented coupling of chemical reactions and diffusion ... 

In the previous section the effects of poisons on reaction rates were related to the active component surface, while the influence of mass transfer was disregarded. It has long been recognized, of course, that the overall rate and selectivity of chemical reactions in porous systems involves the coupling of chemical reactions with convective and diffusive mass transfer processes. Beginning with the pioneering work of Thiele (67), an entire discipline has evolved in which model systems are used to... 

Complexity in multiphase processes arises predominantly from the coupling of chemical reaction rates to mass transfer rates. Only in special circumstances does the overall reaction rate bear a simple relationship to the limiting chemical reaction rate. Thus, for studies of the chemical reaction mechanism, for which true chemical rates are required allied to known reactant concentrations at the reaction site, the study technique must properly differentiate the mass transfer and chemical reaction components of the overall rate. The coupling can be influenced by several physical factors, and may differently affect the desired process and undesired competing processes. Process selectivities, which are determined by relative chemical reaction rates (see Chapter 2), can thenbe modulated by the physical characteristics of the reaction system. These physical characteristics can be equilibrium related, in particular to reactant and product solubilities or distribution coefficients, or maybe related to the mass transfer properties imposed on the reaction by the flow properties of the system. 

Excluding the coupling of chemical reactions with the heat and mass flows, and using the relationship AfiA = (dprA/dCA)ACA, Eq. (9.54) reduces to... 

Example 9.8 Stationary coupling of chemical reactions with heat and mass flows Stationary forms of Eqs. (9.150) and (9.151) are... 

U. Maas, Coupling of Chemical Reaction With Flow and Molecular Transport, Appl. Math. 40 (1995) 249-266. 

The method described here to account for variations of porosity and mass diffusivity associated with precipitation/dissolution of reactive solids provides coupling of chemical reactions to mass transport. The method does not allow the physically impossible exceedance of available pore volume by precipitated solids. 

As a result of this coupling of chemical reactions, it is quite possible for a reaction to occur extensively, even though it has a positive value of AG°. Thus, for the scheme given above, suppose that reaction (1) has a positive value ... 

Coupled reactions. The most obvious role of enzymes is to accelerate reactions, but a second critical role is to couple reactions that would ordinarily be unrelated. From what you have learned from the text and the Conceptual Insights module on energetic coupling, explain why the coupling of chemical reactions in a single enzyme is critical for life. 

The balance in vital processes depends upon the coupling of chemical reactions. In all living cells there occur reactions accompanied by decrease of free energy, and among these the oxidation... 

Hooyman, G.J. Thermodynamic coupling of chemical reactions. Proc. Natl. Acad. Sd. 47, 1169-1173(1961)... 

It is tempting to claim that this equation describes the coupling of chemical reaction and transport. We believe that this is misleading. In fact, this equation describes the perfect decoupling of transport with memory and linear reaction, in line with the main assumption of Model A. To show this, we make the substitution... 

Coupling of chemical reactions in an open system makes possible the occurrence of endergonic reactions forbidden in closed systems, because in these reactions the free energy is increased. 

Example 9.6 Stationary coupling of chemical reactions with heat and mass flows... 

For gaseous flows a huge amount of chemical reaction data is available. Therefore the concentration was focused on combustion problems as a field for examining the coupling of chemical reaction and turbulence. The detailed system of methane-air-combustion has been automatically reduced in order to establish a chemical database for a PDF-approach. The PDF-algorithm has been applied to a combustion problem which is close to realistic flow configurations and the results are compared with experimental data and an other combustion-model. 

The coupling of chemical reaction and turbulence has been demonstrated for the calculation of turbulent diffusion-flames by using a PDF-approach together with a chemical system reduced by the ILDM-method. In general a satisfying agreement of calculations and experiments has been observed. 

Combustion of synthetic (polymeric) polymer materials is characterized by a complex coupling between condensed and gas phase phenomena. Furthermore, the phenomena in each phase consist of a complex coupling of chemical reactions with heat and mass transfer processes. 

In a common industrial heterogeneous catalytic reactor, the data need to include chemical reactions and physical transfer (heat transfer, mass transfer) in varying degrees. It is very difficult to evaluate whether the performance of catalyst is good or not, or to find the way to improve the performance of catalyst according to these combined data. Therefore, it is necessary to dismiss them from the coupling of chemical reactions and physical transfer via appropriate research tools and conditions, to... 

The principle of Le ChStelier asserts that in general a system will react to lessen the effect of a stress on an intensive variable, if it can do so. This effect was illustrated by considering the shift in equilibrium by changing the temperature or the pressure on a system and by adding a reactant or product to the system. The application of the thermodynamics of chemical equilibrium to biological processes was illustrated through a discussion of the coupling of chemical reactions and active transport. 

Skou, J. C., 1977, Coupling of chemical reaction to transport of sodium and potassium, in The Structure of Biological Membranes (S. Abrahamsson and I. Pascher, eds.), pp. 463-478, Plenum Press, New York. 

Describe how the coupling of chemical reactions may make a nonspontaneous process become a spontaneous one. 

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