L9. The Rate and Equilibrium Constants for the Reaction NO₃^•+ Cl^-  -->  Cl^• + NO₃^- in Aqueous Solutions

G. A. Poskrebyshev^a, P. Neta^b, and R. E. Huie^b

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^aInstitute of Energy Problems of Chemical Physics, Russian Academy of Sciences, Moscow 117829, Russia*

E-mail: poskr@nist.gov

^bPhysical and Chemical Properties Division, National Institute of Standards and Technology, Gaithersburg, MD, 20899-8381

E-mail: rhuie@nist.gov

E-mail: pneta@nist.gov

The rate and equilibrium constants for reaction NO₃^· + Cl^- --> Cl^· + NO₃^- in aqueous solutions were studied by pulse radiolysis. The formation and decay of the nitrate radical, NO₃^·, and the dichloride radical, Cl₂^·-, in irradiated aqueous solutions containing nitric acid and chloride ions were followed under various conditions. The rate and equilibrium constants were derived from modeling the experimental results with a complete set of formation and decay reactions. Among the decay reactions is the proposed rapid oxidation of Cl₂^·- to Cl₂ by the NO₃^· radical. By taking the recently published value of k_backward = 1.0 ´ 10⁸ L mol^-1 s^-1, we derive the forward rate constant k_forward = (3.5 ± 0.5) ´ 10⁸ L mol^-1 s^-1 and the equilibrium constant K_eq = (3.5 ± 0.5) at an ionic strength between 0.1 and 1 mol L^-1. In contrast with previous reports, no effect of ionic strength (up to 2 mol L^-1) on the forward rate constant was observed.

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