## Wikipedia - Entropia entropy, $$S$$

https://doi.org/10.1351/goldbook.E02149
Quantity the change in which is equal to the heat brought to the system in a reversible process at constant temperature divided by that temperature. Entropy is zero for an ideally ordered crystal at 0 $$\text{K}$$. In statistical thermodynamics $S=k\ \ln W$ where $$k$$ is the @B00695@ and $$W$$ the number of possible arrangements of the system.
Sources:
Green Book, 2nd ed., p. 48 [Terms] [Book]
PAC, 1990, 62, 2167. (Glossary of atmospheric chemistry terms (Recommendations 1990)) on page 2187 [Terms] [Paper]
PAC, 1996, 68, 957. (Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)) on page 972 [Terms] [Paper]