The four laws of thermodynamics and the entropy

The four laws of thermodynamics define fundamental physical quantities (temperature, energy, and entropy) that characterize thermodynamic systems. The laws describe how these quantities behave under various circumstances, and forbid certain phenomena (such as the perpetuum mobile).

The four laws were developed during the 19th and early 20th century. Many researchers consider that the zeroth and third laws follow directly from the frist and second laws, thus that there are really only two fundamental laws of thermodynamics.

Thermodynamic entropy is a measure of how evenly energy is distributed in a system. The term was coined in 1865 by the German physicist Rudolf Clausius.

In a physical system, entropy provides a measure of the amount of energy that cannot be used to do work.