In the soil environment, reactions are seldom in true equilibrium. Instead, changes in the chemical makeup of the soil solution are constantly affecting the solubility of minerals, the surface charge of solid phases, and sorption and release of trace metals. For these reasons, kinetics (time dependence of reaction) is an important variable in studying the reactivity of soils. Results from novel ATR-FTIR spectroscopic studies conducted in real-time (10 s resolution) will be presented for sulfate adsorption and desorption on several iron oxide mineral phases. Direct evidence for an outer-sphere reaction intermediate followed by a ligand-exchange reaction will be presented and effects of pH and reactant concentration will be discussed. The results from kinetics experiments will also be used to explain the relationship between surface structure, water exchange rates, and reaction mechanisms.