Redox Equilibria and Kinetics

Abstract

Abstract This chapter treats the last of the four major classes of reactions of interest regarding ionic equilibria in natural waters: the coupled processes of oxidation and reduction. Redox processes are important not only for inorganic ions but also play prominent roles in the biogeochemical cycles of important biogenic elements and in transformations of natural organic matter and synthetic organic contaminants. After defining important terms and redox processes, procedures for writing and balancing redox reactions and combining reduction potentials to determine reaction energetics are described, and pε is described as an alternative measure to EH (redox potential). The relationship between reduction potentials and Gibbs free energy of reaction is explained. Procedures for displaying redox equilibria in diagrams are developed. Measurement of redox potential in natural waters and sediments and the limitations of this measurement are presented. The importance of kinetics in describing redox conditions in natural systems is also emphasized.