The last term in this equation is the result of the dissolution of X in Z. Measuring the EMF of this cell determines the activity coefficient of X in the X/Z solution.
Example The following is a modification of the example given in Sect. 10.3. Here X = Ni, Y = Fe, and
Z = Pd (an inert metal). The activity of Ni in the Ni-Pd alloy is 0.5 and the temperature is 1000oC. With so = 0.35 V from the example in Sect. 10.3, Eq (10.11) yields:
1.986 x10-3 x 1273
Dilution of Ni in Pd increases the cell voltage because the tendency of NiO to be converted to Ni is enhanced by depressing the activity of Ni by alloying (Le Chatelier's principle).
Problems 10.1 and 10.6 involve cells with electrodes containing alloys that behave as nonideal solutions.
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