In this final chapter, statistical mechanics is used to develop general theoretical models for the time dependence of chemical transformations within the chemical kineticsChemical kinetics framework. After introducing the Landau free energyLandau free energy, the expression for the unimolecular rate constantRate constant is derived and its relationship with the popular Eyring equationEyring equation is illustrated. Subsequently, a general model for the treatment of bimolecular reactions is outlined in detail. Finally, an exampleExamples is reported dealing with the kinetics of a paradigmatic reaction in organic chemistry: the bimolecular nucleophile substitution reaction in solution.