Halogens, reduction potentials bromine

C. E. Ophardt, "Redox Demon-f strations and Descriptive Chemistry Part 2. Halogens/ /. Chem. Educ., Vol. 64,1987,807. Using an abbreviated table of reduction potentials as a predictive tool, reactions of bromine and iodine in various oxidation states are demonstrated. 

Chemical oxidizers used to disinfect RO systems include hydrogen peroxide (peroxide), halogens, and ozone. Although halogens (and specifically chlorine) are the most popular oxidizers using in conjunction with RO pretreatment, they do not have the highest oxidization-reduction potential (ORP). Table 8.8 lists the ORP for several oxidizers. As the table shows, ozone and peroxide have nearly twice the ORP or oxidative power as chlorine. Despite the relatively low ORP, chlorine is the most commonly used disinfectant in brackish water RO pretreatment due to its ease of use and its ability to provide residual disinfection (for seawater desalination using RO, bromine (as HOBr)... 

The trend in oxidation potentials may be considered a composite trend, similar to that described for the E° values of the alkali metals (Chap. 6). For the halogens, the following quantities are involved heats of dissociation of the molecules, electron affinities of the atoms, hydration energies of the ions, heats of vaporization (for bromine and iodine only), and, finally, entropy or randomness effects. Aside from the entropy effects (which turn out to be quite small for the reactions being considered), the reduction of the halogen X to the hydrated ion X at room temperature may be represented in steps as follows ... 

---