Treatment of Heterogeneous Isotope Exchange

The equations of heterogeneous isotope exchange are simpler than ion-exchange equations because the two ions are chemically the same. In the treatment by the law of mass action, it means that the equilibrium constant is equal to 1. The selectivity coefficients at X = 0 and X = 1 can be determined by measuring heterogeneous isotope exchange in which the concentration of the radioactive isotopes is very low and approaches zero (carrier-free radioactive isotope). 

In the case of heterogeneous isotopic exchange, the ratio of K/K2= 1. From Equation 1.95 we can conclude that 

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