## Entropy

**Entropy** is a thermodynamic property that is the measure of a system’s thermal energy per unit temperature that is unavailable for doing useful work. Perhaps the most familiar manifestation of entropy is that, following the laws of thermodynamics, entropy of a closed system always increases and in heat transfer situations, heat energy is transferred from higher temperature components to lower temperature components. In thermally isolated systems, entropy runs in one direction only (it is not a reversible process). One can measure the entropy of a system to determine the energy not available for work in a thermodynamic process, such as energy conversion, engines, or machines. Such processes and devices can only be driven by convertible energy, and have a theoretical maximum efficiency when converting energy to work. During this work, entropy accumulates in the system, which then dissipates in the form of waste heat.

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### Famous quotes containing the word entropy:

“Just as the constant increase of *entropy* is the basic law of the universe, so it is the basic law of life to be ever more highly structured and to struggle against *entropy*.”

—Václav Havel (b. 1936)