The word entropy, of origin Greek entropía, is a thermodynamic largeness generally associated to the clutter degree. It measures the part of the energy that cannot be transformed into work. It is a state function whose value grows during a process in a closed system.
This concept was created by the physicist and German mathematician Rudolf Clausius, one of the founders of the thermodynamics, formulating the concepts of the Second Law of the Thermodynamics from a reversible cyclical process.
When it is come across with a reversible process, the integral of arched only depends on the states initial and final, independent of the way to be followed. Therefore a function of state of the system must exist, that depends on the volume, temperature and pressure, call of entropy, whose variation in a reversible process represents the states initial and final.
When the ticket of the initial state for the end occurs, the entropy variation is equal the amount of transferred heat divided for the temperature of the process. This largeness allows to basically define the Second Law of the Thermodynamics. Definite as the arrow of the time, therefore, a process tends to give itself of spontaneous form in only direction.
In the year of 1877, the Austrian physicist Ludwig Boltzmann formulated a statistical model for measurement of the entropy of one determined number of particles of an ideal gas. Defining as entropy the proportionality to the neperian logarithms of the number of microstates of a gas. Boltzmann developed its equation, that today meets recorded in its tomb in Vienna. Its death was caused by the depression due little acceptance of its ideas at the time, culminating in its suicide.