The quadratic logistic equation (QLE) is used to determine the number of electrochemical active sites in V2O5 films, by fitting the absorbance changes resulting from the intervalence transfer V(IV) --> V(V) in chronopotentiometry and cyclic voltammetry experiments. Approximately 20% of the V2O5 sites were found to be inactive electrochemically. The absorbance data at 660 nm as a function of the charge injected in layer-by-layer (LBL) films Of V2O5 alternated with poly(ethylene oxide)/chitosan blend was fitted with the QLE, from which the polaronic transfer between V2O5 sites could be investigated. The maximum charge injected was 8 mC cm(-2) for a 15-bilayer LBL film Of V2O5/blend, with ca. 4.0 x 10(-8) mol cm(-2) of electrochemically active V2O5 sites in this film. Departures from the theoretical predictions are interpreted in terms of structural changes in the nanostructured LBL film caused by intercalation of lithium ions. In discussing further applications of the QLE to analyze chemical reactions, it is shown how the number of V(IV) sites is affected by irradiation with a Hg lamp of a 15-bilayer LBL film Of V2O5/blend.