The reaction of dissolution of solid PdCl2 in water-chloride media at room temperature was studied. It was established that the reaction proceeds via a mechanism of topochemical reaction. With the ionic strength fixed, the reaction rate constant is shown to depend on the chloride ion concentration with n = -2, thus confirming that this reaction goes through the formation of hydroxyl and aquachloride complexes of palladium. At low chlorides background С (NaCl) < 0.3 M, and the topochemical nature of the reaction is mainly determined by hydroxide concentration in equilibrium with aquachloride complexes of palladium. The nature and rate of topochemical reaction is determined by concentration of NaCl. With decreasing the concentration of chloride ion from 1 M to 0.2 M reaction proceeds from kinetic to diffusion region.