An electron-spin-resonance study has been carried out, both isothermally and isochronically, of the recovery under vacuum annealing from the hydrogen passivated state (symbolized as HPb) of paramagnetic P-b centers (Si(3)equivalent to Si-.) at the (111)Si/SiO2 interface. Previous work had reported simple exponential decay of [PbH] vs time, taken as key evidence for the process obeying the first-order rate equation d[PbH]/dt = -k(d)[PbH], where k(d)=k(do) exp(-E-d/kT) and E-d the single-valued activation energy. This inference, however, suffered from inadequate data. In contrast, experimental upgrading reveals manifest nonsimple exponential decay, which, within the simple thermal model, reveals the existence of a distinct spread sigma(Ed) in E-d Incorporation of Gaussian spread in E-d leads to a consistent generalized simple thermal model, that matches physical insight. The broad range of data enabled unbiased determination of the physical parameters involved, giving E-d = 2.83 +/- 0.02 eV, sigma(Ed) = 0.08 +/- 0.03 eV, and attempt frequency k(do) = (1.6+/-0.5) X 10(13) s(-1), close to the Si-H waging mode frequency, which provides a clue to the atomic dissociation mechanism. The spread sigma(Ed) results from the interfacial stress-induced Variations in P-b defect morphology. The body of data is found incompatible with second-order kinetics, thus exposing PbH dissociation as an individual process. Combination with the previous generalized thermal model for P-b passivation with H-2 culminates in a consistent unified picture of the P-b-hydrogen interaction kinetics.