Entropy

Definition

Entropy is a measure of the disorder or randomness in a system. It also quantifies the unavailability of a system's energy to do work.

5 Must Know Facts For Your Next Test

1. Entropy always increases in an isolated system according to the Second Law of Thermodynamics.
2. The change in entropy ($\Delta S$) can be calculated using $\Delta S = \frac{Q_{rev}}{T}$, where $Q_{rev}$ is the reversible heat transfer and $T$ is the temperature.
3. In any real process, total entropy (system + surroundings) always increases.
4. Entropy can be seen as a measure of energy dispersal within a system.
5. At absolute zero temperature (0 K), a perfect crystal has zero entropy according to the Third Law of Thermodynamics.

Review Questions

• What does an increase in entropy indicate about the disorder in a system?
• How is the change in entropy ($\Delta S$) calculated for a reversible process?
• Explain why total entropy always increases in real processes.

Related terms

Second Law of Thermodynamics: States that the total entropy of an isolated system can never decrease over time and is constant if all processes are reversible.

$Q_{rev}$: $Q_{rev}$ denotes reversible heat transfer, which occurs without increasing the total entropy of the system plus surroundings.

$\Delta S$: $\Delta S$ represents the change in entropy, often used to quantify how much disorder or randomness has increased or decreased within a system.