An updated and fresh perspective of the subject based on the concepts that the thermodynamic properties of a system are independent whether composition is specified in terms of formal components or molecular species and that the laws of thermodynamics are independent of the observational time-scale. By applying these concepts, the author has derived approximately 20 general theorems concerned with the thermodynamic properties of molecular species and their relationships to those of the formal components. Grunwald defines molecular species to include all participants in reaction mechanisms. Proved theories are supplemented with verbal explanations and explicit examples. Applications chapters include environmental isomers in liquids and thermodynamic properties of water and aqueous systems. Extra thermodynamic chapters feature interionic attraction theory and structure-energy correlation.