The theoretical description of the kinetics of precipitation reactions implicitely uses the assumption of a spatially homogeneous supersaturation in the reactor. In preliminary experiments ii is shown that, since supersaturation is imposed by mixing two reactant solutions, this stands in clear contrast to reality, where a change in hydrodynamic conditions results in different spatial supersaturation patterns, which finally leads to different particle size distributions. Consequently, kinetic expressions derived herefrom will also differ when the same supersaturation, but a different mixing pattern, applies. With a newly developed experimental setup as described here it can be proven that kinetic results become independent from the mixing conditions, i.e. thermodynamically correct, when the reactants are pre-mixed at extremely high Reynolds-Numbers.