A computer aided modeling program is presented. It is based on a generic form of the equations of change in one dimension. A specific model is derived through symbolic manipulation of the basic equations, e.g. skipping of specific terms or extension by detailed flux models. The derivation of a generic balance equation and the following transformation into a user specific model is demonstrated for the component mass balance for a specific example. Consistency of the model is ensured in the model definition step. The output consists of the model in LATEX form including a detailed list of the assumptions and simplifications introduced.