What Is Thermodynamics?
Thermodynamics is the study of the macroscopic behaviour of physical systems under the influence of exchange of work and heat with other systems or their environment. It is not concerned with the microscopic properties of these systems, such as the movements of atoms.
At the very heart of contemporary thermodynamics lies the idea of thermodynamic equilibrium, a state in which no macroscopic properties of the system change over time. In orthodox versions of thermodynamics, properties such as temperature and entropy are defined for equilibrium states only. The assertion that all thermodynamic systems occupying a fixed volume will reach equilibrium in infinite time, which has been central but tacit to thermodynamics, has recently been dubbed the "minus first law of thermodynamics."
Read more about this topic: Philosophy Of Thermal And Statistical Physics