While classical mechanics provides a complete description of the dynamics of a system, the concepts of equilibria require other ideas to be developed. Thermodynamics is the field that describes the macroscopic quantities required for characterizing bulk systems. Traditionally, the so-called laws of thermodynamics prove to be the fundamentals. These laws have been developed over centuries and often have different statements of the same law.
We follow a postulates-based approach to thermodynamics developed in by Herbert Callen.