Molecular dynamics is applied to analyze the association-dissociation process that takes place between contact and solvent-separated ion pairs for aqueous sodium chloride. A flexible single point charge model for water has been assumed. The reactive flux method has been used to compute the forward and backward rate constants. Activated trajectories were sampled according to the constrained reaction coordinate dynamics technique. A detailed study of the influence of the polarization state of the solvent on the reaction rate and of kinetic properties of transition-state recrossings is carried out. The time-dependent friction coefficient on the reaction coordinate has been calculated in order to test the GroteHynes theory. Theoretical predictions are in good agreement with computer simulation results.