Oxidation-Reduction Reactions (Redox)

All of the elements form chemical species that have different oxidation states. Oxidation is the removal of electrons whereas reduction is the addition of electrons to a chemical species. The elements exist on the earth's surface based on their interactions with water, O2, and reductants such as H2S. When thermodynamically favorable electron transfer occurs between reactants, a potential is generated. Electron transfer reactions are termed redox reactions, which can be broken into two separate half-reactions and are readily described by thermodynamics. Most redox reactions involve only one or two electron transfers, and many involve hydrogen ion transfer. Thus, the potential for a half-reaction can vary with pH. Oxygen atom transfer reactions are formally two-electron transfer reactions. In this chapter, the thermodynamic basis for redox reactions and how to predict which chemical species of the elements exists on earth are presented. Example reactions are given in this and subsequent chapters.