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Europium(III) Catalysis for Reduction of Thionine Dye by Selenous Acid in Aqueous Sulfuric Acid Solutions: A Kinetic and Mechanistic Approach
Author(s) -
Fawzy Ahmed
Publication year - 2016
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.21012
Subject(s) - chemistry , europium , thionine , sulfuric acid , reaction rate constant , ionic strength , catalysis , aqueous solution , inorganic chemistry , reaction rate , equilibrium constant , ionic bonding , kinetics , ion , organic chemistry , electrochemistry , electrode , physics , quantum mechanics
The catalytic effect of europium(III) on the reduction of thionine dye (Th) by selenous acid has been studied by spectrophotometry in aqueous sulfuric acid solutions at a constant ionic strength of 3.0 mol dm −3 and at different temperatures (283–313 K). A first‐order dependence with respect to both [Th] and [Eu III ] was obtained, whereas the orders with respect to [Se IV ] and [H + ] were less than unity. Variation of ionic strength and dielectric constant of the reaction media did not affect the reaction rates. Probable mechanistic schemes for thionine reductions in both the absence and presence of europium(III) catalyst were proposed. The rate laws associated with the reaction mechanisms were derived, and the reaction constants were calculated. The activation parameters of the rate constants of the slow steps of both uncatalyzed and catalyzed reactions along with thermodynamic quantities of the equilibrium constants are computed and discussed.