Entropy (S)

Definition

Entropy (S) is a measure of the disorder or randomness in a system. It quantifies the number of possible microstates corresponding to a macroscopic state.

5 Must Know Facts For Your Next Test

1. Entropy increases in spontaneous processes and reaches a maximum at equilibrium.
2. The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time.
3. Entropy can be calculated using the formula $\Delta S = \frac{q_{rev}}{T}$, where $q_{rev}$ is the reversible heat transfer and $T$ is the temperature in Kelvin.
4. Standard molar entropy ($S^{\circ}$) values are used to calculate changes in entropy for chemical reactions.
5. In statistical mechanics, entropy is related to the number of microstates (W) by the Boltzmann equation: $S = k_B \ln W$, where $k_B$ is Boltzmann's constant.

Related terms

Second Law of Thermodynamics:

States that the total entropy of an isolated system can never decrease over time; it can only stay constant or increase.

Microstate: A specific detailed microscopic configuration of a system.

$\Delta G$ (Gibbs Free Energy): $\Delta G = \Delta H - T \Delta S$, which determines if a process is spontaneous when $\Delta G < 0$.