Thermodynamic control, transport rate constants

Eqs. 95 and 96 could be derived for the dependence of the transport rate constants ki (from the aqueous phase into the organic phase) and the reverse rate constants kj (from the organic phase into the aqueous phase) on lipophilicity [444]. According to eq. 95, the rate constants ki are thermodynamically controlled, they linearly increase with lipophilicity. With further increase in lipophilicity the diffusion of the solutes becomes rate-limiting a plateau is reached because now thermodynamic control is replaced by kinetic control. The reverse holds true for the rate constants k2 (eq. 96) (Figure 16). 

Equilibrium partitioning and mass transfer relationships that control the fate of HOPs in CRM and in different phases in the environment were presented in this chapter. Partitioning relationships were derived from thermodynamic principles for air, liquid, and solid phases, and they were used to determine the driving force for mass transfer. Diffusion coefficients were examined and those in water were much greater than those in air. Mass transfer relationships were developed for both transport within phases, and transport between phases. Several analytical solutions for mass transfer were examined and applied to relevant problems using calculated diffusion coefficients or mass transfer rate constants obtained from the literature. The equations and approaches used in this chapter can be used to evaluate partitioning and transport of HOP in CRM and the environment. 

While the conversion of a supramolecular complex back into its constituent components is part of the equilibration process and, as such, is contained in thermodynamic selectivity, any alternative transformation leading to a function is characterized by a rate and a corresponding monomolecular rate constant. Principally, it can refer to just one elementary reaction yielding the function, but more likely, function generation will be composed of several successive steps. In any case, a pathway is defined that features a certain activation barrier that, in turn, determines the total flux on this route. Typical kinetically controlled vectorial processes include the transport of compounds across membranes, the photosynthetic elec-... 

The fundamental question in transport theory is Can one describe processes in nonequilibrium systems with the help of (local) thermodynamic functions of state (thermodynamic variables) This question can only be checked experimentally. On an atomic level, statistical mechanics is the appropriate theory. Since the entropy, 5, is the characteristic function for the formulation of equilibria (in a closed system), the deviation, SS, from the equilibrium value, S0, is the function which we need to use for the description of non-equilibria. Since we are interested in processes (i.e., changes in a system over time), the entropy production rate a = SS is the relevant function in irreversible thermodynamics. Irreversible processes involve linear reactions (rates 55) as well as nonlinear ones. We will be mainly concerned with processes that occur near equilibrium and so we can linearize the kinetic equations. The early development of this theory was mainly due to the Norwegian Lars Onsager. Let us regard the entropy S(a,/3,. ..) as a function of the (extensive) state variables a,/ ,. .. .which are either constant (fi,.. .) or can be controlled and measured (a). In terms of the entropy production rate, we have (9a/0f=a)... 

---