A mechanistic model was developed to study the industrial synthesis of the polyurethane precursor, amine hydrochloride, in a confined impinging jet reactor (CUR). Two chemical reaction steps occur in a competitive-consecutive sequence, which results in the precipitation of two amine hydrochloride salts. The formation of the di-amine byproduct means loss of starting material and expensive reprocessing of highly insoluble salts. The predictive mechanistic model includes equations for chemical reaction kinetics, nucleation, particle growth, and the first reported mixing model for the CIJR. In our previous study [Maluta, F. et al. Comput. Chem. Eng. 2017, 106, 322], we used a full factorial design to determine physically realizable values of the 11 physical constants involved in the model. In this study, we show the importance of using a mixing model to account for imperfect mixing in the impingement zone. The mixing model treats the impingement zone as a radial jet and resolves the local mixing into 198 discrete compartments. The model was able to predict an unexpected and sudden change in the reaction product distribution as the reactant inlet concentration is increased. Without the local mixing model, it was not possible to replicate this major trend in the experimental results. The local mixing model allows us to determine the conditions under which significant byproduct formation will occur. A second industrially important question is whether fine particles or larger particles will be produced. This process outcome was also dominated by local mixing conditions in the impingement region. The model results show a strong influence of local mixing on two key process outcomes.