Valence States in Oxidation-Reduction Reactions

Intermediate Valence States in Oxidation-Reduction Reactions 

The analogue of free radicals for inorganic ions would be intermediate valence states, and many of the kinetic results on redox reactions have required the postulation of unstable valence states for inorganic ions. One of the classic studies of this type is the slow reaction 2Fe + Sn++ 2Fe + Sn +. The reaction is very slow in HCIO4 solution but is strongly catalyzed by C1-. At high Fe +/Sn++ ratios, the rate law has the form 

Such a rate law cannot be explained without postulating an unstable valence state such as Fc + or Sn +. Weiss has proposed a mechanism involving the latter which is in good agreement with the data over a considerable range  

By applying the stationary-state treatment to SnCl we find for the over-all rate 

When A2(Fe++) fc3(Fe ) this reduces to the expression found by Noyes (Joe. cit.) on adding Fe + initially  

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