Recent moment theories of ion motion in traps and similar devices are extended to mixtures of neutral gases in which one or more components can undergo infrequent reaction with the ion of interest. Expressions are developed for the position and time dependence of the ion-neutral reaction rate coefficient in such circumstances. These expressions are incorporated into the sets of coupled differential equations that govern the average ion velocity and kinetic and internal energies. This provides a consistent description of the ion transport and reaction coefficients.