Entropy

Definition

Entropy is a measure of the disorder or randomness in a system. It quantifies the number of possible microscopic configurations that correspond to a thermodynamic system's macroscopic state.

5 Must Know Facts For Your Next Test

1. Entropy tends to increase in isolated systems, consistent with the Second Law of Thermodynamics.
2. The change in entropy ($\Delta S$) for a reversible process can be calculated using $\Delta S = \int \frac{dQ_{rev}}{T}$, where $dQ_{rev}$ is the infinitesimal heat added reversibly and $T$ is the temperature.
3. In any spontaneous process, the total entropy of the system and its surroundings always increases.
4. Entropy is often associated with energy dispersal within a system; higher entropy means greater dispersal of energy.
5. The units of entropy are typically joules per kelvin (J/K).

Review Questions

• What does an increase in entropy indicate about the disorder of a system?
• How is the change in entropy calculated for a reversible process?
• Why does the total entropy of an isolated system never decrease?

Related terms

Second Law of Thermodynamics:

A law stating that in any cyclic process, the entropy will either increase or remain unchanged.

Reversible Process:

A theoretical process that occurs infinitely slowly so that the system remains in thermodynamic equilibrium.

Heat (Q): A form of energy transfer between bodies or thermodynamic systems due to a temperature difference.