Entropy

Entropy, abbreviated as S, (English unit \(\frac{Btu}{lbm-R}\), Metric unit \(\frac{kJ}{kg-K}\)), measures the unavailable energy in a heat system.  It is a measure of the disorder of a system and of its constituent molecules.  In thermodynamics it is a measure of the unavailability of a system's energy fo do work.

• See Second Law of Thermodynamics