The Kinetics of the Exchange Reaction between the Two Oxidation States of Cerium in Acid Solution<sup>1a</sup>

Gryder, J. W.; Dodson, R. W.

doi:10.1021/ja01150a138

Cited by 41 publications

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“…Similarly, these do not enter into the pre-exponential term for solution phase reactions, provided, of course, that the slow step is electron transfer. Laidler's expression (21) will be useful in estimating the rates of electron-transfer reactions for which the overall free energy is so negative that the slow step is diffusion.…”

Section: T H T Rate Constantmentioning

confidence: 99%

Adiabatic theory of outer sphere electron-transfer reactions in solution

Hush¹

1961

Trans. Faraday Soc.

845

475

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Section: T H T Rate Constantmentioning

confidence: 99%

Adiabatic theory of outer sphere electron-transfer reactions in solution

Hush¹

1961

Trans. Faraday Soc.

845

475

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“…Assuming that d(Uv)/dt = 0, this scheme leads directly to the observed rate expression (Equation [2] above). T h e factor 2 in Equation [2] arises from the fact that for every Fe(I1) formed in Reaction 171, a second Fe(I1) is formed by Reaction [8]. * The absence of terms like (U1V)2 or (Fe111)2 in the empirical rate expression rules out any significant contribution from dimeric ions, e.g., (FeOHFe)+5; this ion is known to be present a t very low concentration in aqueous solutions of ferric salts (9, 15).…”

Section: Stoichiometry and Kinetic Order Of The Reactionmentioning

confidence: 99%

“…The doubly hydrolyzed ion Fe(OH)2+ is also present a t very low concentration (8,9,16,17): Although there is no quantitative information available, it is reasonable to assume, by analogy with the chemistry of iron (111), that the ion U(OH)2++ also is present a t very low concentration:…”

Section: Effect Of Hydrogen-ion Concentrationmentioning

confidence: 99%

“…However recent studies with radioactive tracers have shown that even such elementary reactions as electron transfer between iron (11) and iron (I 11), or between Ce (I 11) and Ce (IV), do not proceed instantaneously (18,8). Such results have reawakened interest in the whole subject of both isotopic and ilo~lisotopic electron transfer reactioils between cations in solution.…”

Section: Introductionmentioning

confidence: 99%

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Kinetics of the Oxidation of Uranium (Iv) by Iron (Iii) in Aqueous Solutions of Perchloric Acid

Betts¹

1955

Can. J. Chem.

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The kinetics of oxidation of uranium (IV) b y iron (111) in aqueous solutions of perchloric acid have been investigated a t four temperatures between 3.1°C. and 24.8"C. The reaction was followed by measurement of the amount of ferrous ion formed. For the conditions (Il+) = 0.1-1.0 iM, ionic strength = 1.02, (FelII) = 10-'-10-5 hf, and (UIV) = lO-'-lO-6 ill, the observed rate law is d(FeZ+)/dt = -2d(UIV) /dt -K1 and Kn are the first hydrolysis constants for Fe3+ and U4+, respectively, and K'and K" are pseudo rate constants. At 24.8"C., K' = 2.98 sec.-I, and K" = 10.6 mole liter-' sec-'. The corresponding temperature coefficients are AH' = 22.5 kcal./mole and AH" = 24.2 kcal./mole. The kinetics of the process are consistent with a mechanism which involves, as a rate-controlling step, electron transfer between hydrolyzed ions. INTRODUCTIONOxidation-reduction reactions between cations in aqueous solution have been thought until recently t o proceed very rapidly, and the term "instantaneous" has frequently been used to characterize their rates. However recent studies with radioactive tracers have shown that even such elementary reactions as electron transfer between iron (11) and iron (I 11), or between Ce (I 11) and Ce (IV), do not proceed instantaneously (18,8). Such results have reawakened interest in the whole subject of both isotopic and ilo~lisotopic electron transfer reactioils between cations in solution. Some kinetic information is now available relating to the reactioils between the nonisotopic pairs Sn (11) -Fe (111) (5), T1 (111) -Fe (11) (2), and N p (IV) -Fe (111) (10).Several review articles have recently appeared in which the current status of theory and experiment have been summarized for both isotopic and nonisotopic clcctron transfer reactioils (1,14,19). The proceedings of a symposium held in 1954 on this subject have also been published (12).As a further example of this type of reaction, the present paper describes experiments relating to the kinetics of the oxidatioil of uranium (IV) by iron (111) in aqueous acidic media. Perchloric acid and sodium perchlorate were chosen as the principal electrolytes, since amongst the common inorganic anions, perchlorate has the least tendency to form ion-pairs with cations. T o bring the rate of reaction into a range suitable for study, it has been necessary to work with solutions to 10-5 M in uranium (IV) and iron (111). T h e course of the reaction has been followecl by measurement of the rate of formatioil of iron (11). Such measurements, in conju~lction with a knowledge of the stoichiometry of the reaction, were sufficient to enable a kinetic analysis of the results to be made. I t would have been useful, as confirmatory evidence, lMa?zz~script

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“…Other workers have shown the influence of nitrate ions on the rate of inorganic oxidation-reduction reactions to be slight 2- 6 which is in accord with the fact that oxy-anions such as nitrate only form weak ion-pairs with cations and thus cannot affect their rcactivity appreciably. On the other hand, fluoride ions have been shown to have a marked effect on the rate of electron exchange reactions such as Fe (11) + Fe(III),7 Ce(II1) + Ce(IV),s and Cr(I1) + Cr(II1) : 9, 10 for the latter reaction a bridge transfer involving the fluoride ion was established.9 EXPERIMENTAL MATERIALS SODIUM FLUORIDE.-The B.D.H. "…”

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confidence: 67%

The reaction between cerium (III) and cobalt (III). Part 2.—The effect of nitrate and of fluoride ions

Sutcliffe¹,

Weber²

1959

Trans. Faraday Soc.

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A further study of the Co(II1) + Ce(II1) reaction has been made in order to investigate the influence of nitrate and of fluoride ions. Although fluoride ions produce a much more marked acceleration of the reaction rate than do nitrate ions, both appear to participate in similar mechanisms, namely, the two competing paths,where Xis either a nitrate or a fluoride ion.From a spectrophotometric investigation the heat and entropy of formation of CeNO; +were found to be -7 k 2 kcal mole-1 and -23 f 7 cal mole-1 deg.-l respectively at 25°C for an ionic strength of 1.0 M. Using these data the true energy and entropy of activation of the nitrate-accelerated path were calculated to be 14 i 2 kcal mole-1 and-5 -+ 1 cal mole-1 deg.-l respectively at 25°C for an ionic strength of 1.0 M.

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The Kinetics of the Exchange Reaction between the Two Oxidation States of Cerium in Acid Solution^1a

Cited by 41 publications

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Adiabatic theory of outer sphere electron-transfer reactions in solution

Adiabatic theory of outer sphere electron-transfer reactions in solution

Kinetics of the Oxidation of Uranium (Iv) by Iron (Iii) in Aqueous Solutions of Perchloric Acid

The reaction between cerium (III) and cobalt (III). Part 2.—The effect of nitrate and of fluoride ions

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The Kinetics of the Exchange Reaction between the Two Oxidation States of Cerium in Acid Solution1a

Cited by 41 publications

References 0 publications

Adiabatic theory of outer sphere electron-transfer reactions in solution

Adiabatic theory of outer sphere electron-transfer reactions in solution

Kinetics of the Oxidation of Uranium (Iv) by Iron (Iii) in Aqueous Solutions of Perchloric Acid

The reaction between cerium (III) and cobalt (III). Part 2.—The effect of nitrate and of fluoride ions

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The Kinetics of the Exchange Reaction between the Two Oxidation States of Cerium in Acid Solution^1a