Estimation of flow in a diffusion cell

the externally established potential difference causes a concentration gradient and hence a flow, provided that the mobilities of the ions are different (Garby and Larsen, 1995). Due to electroneutrality, the local concentrations of Na+ and Cl- ions are the same, and are denoted by cx(x). Also, the flows of negative and positive ions are the same, J+ = J.  

The flows of ions are oppositely directed. Using the Nernst-Planck equation at constant T and P for Na+ and Cl- ions and eliminating the flows yields 

This equation shows the magnitude of an externally induced concentration gradient. The gradient is zero if b + = b, which is nearly true forKCl. The flow of NaCl can be obtained by substituting Eq. (10.81) into Fick s law 

For arbitrary ionic valences, the flow may be obtained from 

For composite membranes (with compartments) the dissipation function F in terms of flows of volume, salt, and electric current, and the corresponding forces are 

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Example 10.6 Estimation of flow in a diffusion cell Each chamber of the diffusion cell shown in Figure 10.2 has an aqueous solution of NaCl with concentrations c1A = cXB = 100 mmol/L at 298 K. An electric potential difference of 100 mV is established between the two chambers. Estimate the diffusion flow of NaCl and its direction if... 

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