Entropy (classical Thermodynamics)

Entropy (classical Thermodynamics)

Entropy is a property of thermodynamical systems. A thermodynamic system is any physical object or region of space that can be described by its thermodynamic quantities such as temperature, pressure, volume, and density.

The concept of entropy was developed by Rudolf Clausius. Clausius gave it the name "entropy", from the Greek word τρoπή, "transformation". It makes no reference to the microscopic nature of matter. In the 1870s Ludwig Boltzmann described the entropy as a measure of the number of possible microscopic configurations Ω of the individual atoms and molecules of the system (microstates) which comply with the macroscopic state (macrostate) of the system. Boltzmann then went on to show that klnΩ was equal to the thermodynamic entropy. The factor k has since been known as Boltzmann's constant.

This article is concerned with the thermodynamic definition of entropy. Although thermodynamic entropy is a self-contained subject, it should be understood in parallel with the statistical definition. When the thermodynamic definition becomes most difficult to understand, the statistical definition brings a simple explanation, and where the link between the statistical theory and experiment becomes extended, the thermodynamic theory delivers a straightforward answer.