Third law of thermodynamics

Definition

The third law of thermodynamics states that the entropy of a perfect crystalline substance approaches zero as the temperature approaches absolute zero. This implies it is impossible to reach absolute zero in a finite number of steps.

5 Must Know Facts For Your Next Test

1. At absolute zero, the entropy of a perfect crystal is exactly zero.
2. Absolute zero is theoretically unattainable through any physical process.
3. The third law helps in understanding the behavior of materials at very low temperatures.
4. Entropy quantifies the disorder or randomness in a system, and this law provides a reference point for it.
5. This law has implications for calculating thermodynamic properties and efficiencies at low temperatures.

Review Questions

• What does the third law of thermodynamics state about entropy at absolute zero?
• Why is it impossible to reach absolute zero in practice according to the third law?
• How does the third law of thermodynamics assist in understanding material behavior at low temperatures?

Related terms

Entropy:

A measure of the disorder or randomness in a system.

Absolute Zero:

The lowest possible temperature where all molecular motion ceases, defined as $0\ \text{K}$ or $-273.15\ ^\circ \text{C}$.

Second Law of Thermodynamics:

$\Delta S_{universe} \geq 0$: States that in any natural process, the total entropy of a system and its surroundings always increases.