3. Thermodynamic properties

In principle, statistical mechanics enables us to calculate the enthalpy, entropy and heat capacities of any substance described by a molecular model. These properties are obviously of prime importance in chemical engineering, whether for predicting the direction of a reaction, the amount of heat released or absorbed per mole transformed, or the optimum total pressure at which the process should operate. The evaluation of thermochemical functions is therefore one of the most recurrent applications of molecular modeling. Conversely, the highly accurate thermochemical data available for a large number of pure bodies provides very demanding tests for theoretical methods, and in particular for quantum chemical methods.