Potential and Escaping Tendency

Lewis proposed the term escaping tendency to give a strong kinetic-molecular flavor to the concept of the chemical potential. Let us consider two solutions of iodine, in water and carbon tetrachloride, which have reached equilibrium with each other at a flxed pressure and temperature (Fig. 9.2). In this system at equilibrium, let us carry out a transfer of an inflnitesimal quantity of iodine from the water phase to the carbon tetrachloride phase. On the basis of Equation (9.17), we can say that 

In this closed system, any loss of iodine from the water phase is accompanied by an equivalent gain in the carbon tetrachloride thus. 

It also may be helpful to consider the situation in which the iodine will diffuse spontaneously (at constant pressure and temperature) from the water into the carbon tetrachloride, a case in which the concentration in the water phase is greater than that which would exist in equilibrium with the carbon tetrachloride phase. From Equation (9.17), we can write 

For the spontaneous diffusion of iodine. Equation (9.39) is valid in this closed system. Hence, 

That is, dn is a negative number. In such a case. Equation (9.44) is valid only if the difference in chemical potentials is a positive number. Therefore 

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