Activation energy for transport

Our data at three temperatures on KCl do not permit activation energies to be evaluated with precision. Clearly the activation energy for transport in the polymer is considerably larger than it is in free solution and seems larger for Cl" than for K+. 

Membrane proteins lower the activation energy for transport of polar compounds and ions by providing an alternative path through the bilayer for specific solutes. Proteins that bring about this facilitated diffusion, or passive transport, are not enzymes in the usual sense their substrates are moved from one compartment to another, but are not chemically altered. Membrane proteins that speed the movement of a solute across a membrane by facilitating diffusion are called transporters or permeases. 

Hops from deep sites to nearby, higher-energy sites contribute to the activation energy for transport. At lower and lower temperature, that contribution increases because a carrier spends most of its time in deeper and deeper sites. The apparent temperature-dependent activation energy mentioned in conjunction with Eq. (5) is easily understood on this basis. (Of course, any reorganization energy for the electron transfer process may also contribute to the temperature dependence.)... 

With the simplification allowed by this inequality in equations (9.30), (9.32), (9.34) and (9.35) it is now possible to determine a variety of important quantities. The temperature-dependence of the static conductivity gives an activation energy which is equal to the sum of half the energy for formation of a pair of ion states and the activation energy for transport of the more mobile ion state. Thus = 0-48 0-07 eV. (9.36)... 

Since tanh

sufficiently large Thiele moduli, it follows from Eq. 29 that the effectiveness factor approaches the reciprocal value of the Thiele modulus. In the classical Thiele concept, this leads to the well-known reduction in the apparent activation energy for transport-controlled reactions, since the effective reactivity is now proportional to Vk rather than to fc, as in the absence of any transport limitation. 

Godino PM, Barragm VM, Izquierdo MA, Villaluenga JPG, Seoane B, Ruiz-Bauza C (2009) Study of the activation energy for transport of water and methanol through a Nafion membrane. Chem Eng J 152 20-25... 

The respective values of Ep and Ep p calculated from Fig.5 are about 4.8 Kcal/mole and 2.3 l cal/mole respectively the low activation energy of the isothermal process being indicative of a viscous flow mechanism while.the relatively higher value of Ep j is comparable with those generally found in diffusive processes (17-19). The concept of apparent activation energies for transport in a temperature gradient arises from the different dissolution enthalpies of the permeant on opposite partition sides. From the definition of enthalpy it follows that... 

In interpreting observations of nucleation phenomena the activation energy for transport across the nucleus-matrix interface AG has generally been equated with that for transport in bulk liquid, AG. In principle these... 

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