Only three references about the reactions of ammonia (NH3) with dinitrogen pentoxide (N2O5) have been published in the course of the last 150 years. None of them describes the reactions referring to the products in dependence on the reaction conditions. In this report the experimental results due to the reaction of NH3 and N2O5 lead to three equations. One of these, the formation of dinitrogen oxide (N2O) in addition to ammonium nitrate (NH4NO3; AN) was not mentioned before in the references available. The other reactions are known as the formation of ammonium dinitramide (NH4N(NO2)(2); ADN) and AN beside the formation and decomposition of nitramide (NH2NO2; NA) into water and dinitrogen oxide. Summarizing the known reactions of NH3 with N2O5 and those of the intermediate products in a reaction scheme a model was established for the selectivity of ammonium dinitramide (ADN) and for the dependence on the reaction conditions. The model is in good accordance with the experimental results.