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Inorganic reactions of iodine(III) in acidic solutions and free energy of iodous acid formation
Author(s) -
Schmitz Guy
Publication year - 2008
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.20344
Subject(s) - chemistry , gibbs free energy , protonation , reaction rate constant , ionic strength , equilibrium constant , iodide , medicinal chemistry , iodine , reaction rate , activation energy , kinetic energy , kinetics , inorganic chemistry , thermodynamics , ion , organic chemistry , catalysis , aqueous solution , physics , quantum mechanics
An analysis of the former works devoted to the reactions of I(III) in acidic nonbuffered solutions gives new thermodynamic and kinetic information. At low iodide concentrations, the rate law of the reaction IO − 3+ I − + 2H + ⇌ IO 2 H + IOH is k +B [IO − 3 ][I − ][H + ] 2 – k −B [IO 2 H][IOH] with k +B = 4.5 × 10 3 M −3 s −1 and k −B = 240 M −1 s −1 at 25°C and zero ionic strength. The rate law of the reaction IO 2 H + I − + H + ⇌ 2IOH is k +C [IO 2 H][I − ][H + ] – k −C [IOH] 2 with k +C = 1.9 × 10 10 M −2 s −1 and k −C = 25 M −1 s −1 . These values lead to a Gibbs free energy of IO 2 H formation of −95 kJ mol −1 . The pK a of iodous acid should be about 6, leading to a Gibbs free energy of IO − 2formation of about −61 kJ mol −1 . Estimations of the four rate constants at 50°C give, respectively, 1.2 × 10 4 M −3 s −1 , 590 M −1 s −1 , 2 × 10 9 M −2 s −1 , and 20 M −1 s −1 . Mechanisms of these reactions involving the protonation IO 2 H + H + ⇌ IO 2 H + 2and an explanation of the decrease of the last two rate constants when the temperature increases, are proposed. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 647–652, 2008