This is the final report of a three year Laboratory Directed Research and Development, LDRD, project in which we investigated the kinetic mechanisms of two important classes of heterogeneous reactions in the stratosphere, hydrolysis and reaction with HC1. Utilizing a combination of experimental techniques unique to our laboratory at Los Alamos, and applying a very successful program of modeling, we have proposed a model of stratospheric hydrolysis which enables calculation of uptake coefficients in agreement with essentially all of the data in the literature, and have produced the first thermodynamically consistent model of the adsorption of HC1 on two ice surfaces believed to be important in the stratosphere. Among the conclusions of this work, we have shown that the uptake of HC1 on these surfaces in consistent with the classic HC at O binary phase diagram, and that such uptake is too small for HC1 to serve as a surface adsorbed reagent under most conditions, as had been previously believed.