Question

12. Describe the three main modes of mass transfer in electrochemical cells. How can mass transfer from migration be minimized?

Answer 1

There are three fundamental modes of mass transport in solutim These are : 9 migration 6) Difusion e) convection. a) migration migration happens due to movement of charged particles in presence of local electric field. The migratery flex induced can be described in dlo. - Mc () at The contribution of migration to the total flux in proportional to the charge of theion, the ion concentration, and the magnitude of the elechic field gradient experienced by the ion.

6) Diffusion Ono Eco 0 Diffusion in the random morment of the molecules from a high concentration region to a lower concentration region. The rate at which a molecule diffuses is dependent upon the difference in concentration between two points in solution and the Diffusion Diffusion coefficient. The rate of movement of material by diffasin can be quedicted by Fick's law. Fick's first law To = The rate of movement of material by diffusim = Diffusional flux Do= Diffusim o efficient concentration sign The negative signifies that material mores down a comemoration gradient, ine, leigh concentration region to lower concentration gradient

Fick's second law 200Do ) ot Rate of change of the concentration as a function of time can be related to the change in the change in concentration gradient and the diffusim co. effiont. So, tue. Steepen the change. low comentation the ligner the rate of diffusion. I connection Convection related to buy ano dynamic vorberty Two types of hy fro dynamic transport- i gratural conrection Due to density gradients. 4 Forced conroetin Dve to external means, as for example Stirring V = The volocity of the solution

++Addition of an excess of nonelectroactive ion or a supporting electrolyte ( an inert ion) minimized the mass transfer from migration.