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Kinetics of copper reduction by hydrogen from aquaeous solutions. Hahn, Edmund Alexander Joachim

Abstract

The kinetics of the hydrogen reduction of aqueous cupric perchlorate and sulphate solutions were studied at 160°C and 5 to 10 atm hydrogen pressure. In sulphate solutions the observed rates were consistent with a rate law, derived from previously proposed mechanisms, that has the form [ Equations omitted ] The rate constants of the hydrogen activation steps of the reaction are represented by k₁and k₃ which reflect the activation rates by Cu'' and Cu' respectively and have the values 3.2 X 10¯³M¯¹sec¯¹ and 6.4 X 10¯²M¯¹sec¯¹ at 160°C. The ratios of the back- to net forward-reaction rate constants are k-₁/k₂ for the Cu'' activation step and k-₃/k₄ for the Cu' activation step. These have values of approximately 0.13 and 0.45 respectively at 160°C. In perchlorate solutions the rates were also consistent with the rate law applying to sulphate solutions if a necessary correction due to perchlorate decomposition was taken into account. In this system the second term of this rate law was found to be much smaller and more difficult to resolve. For the first term the value of k₁ was found to be 6.7 X 10¯³M¯¹sec¯¹ at 160°C and the value of k-₁/k₂ was 0.51. Exchange experiments with deuterium in place of hydrogen were also done. These gave rates consistent with previously proposed mechanisms, but in perchlorate solutions much higher exchange rates were observed than in sulphate solutions. The indicated value of k₃ is approximately the same in perchlorate as in sulphate solutions and the indicated value of k-₃/k₄ is much greater in perchlorate solutions.

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