Glossary
Second Law of Thermodynamics
In the 1850s Clausius and Kelvin independently formulated the second law of thermodynamics. Clausius invented the term entropy, S, to provide a measure of the "transformational content" (capacity for change). The term means transformation, from the Greek word τροπη.
The second law of thermodynamics states that, on average, the entropy of a closed system can only increase (in an irreversible reaction) or stay constant (in equilibrium):
dS / dt ≥ 0
where S is the entropy and t is time.
It is worth emphasizing that at any given instant the entropy of a closed system can actually decrease. The probability of such an event, however, is extremely small.
The second law of thermodynamics and entropy are related through the following mathematical relationship:
dS ≥ dQ / T
where dQ is the amount of heat absorbed, and T is the absolute temperature.