An exchange reaction is a reaction in which an atom in a molecule interchanges with a chemically identical atom in some other state of chemical combination. The reaction may be represented by the equation AB + B*C = AB* + BC where B and B* represent atoms which are chemically identical but physically distinguishable. To follow the course of the reaction there must be some means of completely separating AB and BC after allowing them to mix and react for a given time. In addition, for quantitative calculations of the exchange, the physical property which distinguishes the atom must be a function of the concentration of the labelled atoms. The discovery of isotopes of the elements provided the necessary condition of chemically identical atoms which are physically distinguishable. If B represents the natural mixture of isotopes of an element and B* represents a mixture containing an excess of one particular isotope the difference in mass will serve to distinguish B and B*. If B* is a radioactive isotope of the element represented by B, this also will serve as a means of distinguishing B and B*. The use of stable isotopes generally requires more elaborate equipment and procedures for quantitative analyses than does the use of radioactive isotopes.

Winkler, C. (Supervisor)