Estimation methods developed over years by S. W. Benson and co-workers for calculation the thermodynamic properties of organic
compounds in the gas phase are applied to a pharmaceutical real process with all type of non-idealities. The different strategies
used to calculate the reaction enthalpy of a chemical process, in the absence of data for complex molecules, using the Benson
group additivity method are presented and also compared with the experimental value of reaction enthalpy obtained using reaction
calorimetry (Mettler-Toledo, RC1). We demonstrate that there are some strategies that can be followed to obtain a good estimation
of the reaction enthalpy in order to begin the safety assessment of a chemical reaction. This work is part of an industrial
project  in which the main objective was the risk assessment of chemical real and complex processes using the commonly
available tools for the SMEs (with limited resources).