Third law of thermodynamics

Definition

The third law of thermodynamics states that the entropy of a perfect crystal at absolute zero temperature is exactly zero. This implies that it is impossible to reach absolute zero in a finite number of steps.

5 Must Know Facts For Your Next Test

1. Entropy approaches zero as the temperature approaches absolute zero for a perfect crystal.
2. It is physically impossible to reach absolute zero temperature.
3. The third law helps define the concept of absolute entropy.
4. Residual entropy can exist in non-perfect crystals even at absolute zero due to disorder.
5. The third law implies that as temperature decreases, the entropy change associated with any process also decreases.

Review Questions

• What happens to the entropy of a perfect crystal at absolute zero according to the third law of thermodynamics?
• Why is it impossible to reach absolute zero temperature?
• How does the third law relate to the concept of residual entropy?

Related terms

Entropy:

A measure of disorder or randomness in a system. In thermodynamics, it quantifies how much energy in a system is unavailable for doing work.

Absolute Zero:

$0 \text{ K}$, theoretically the lowest possible temperature where all thermal motion ceases.

Second Law of Thermodynamics:

$\Delta S_{universe} \geq 0$: Entropy of an isolated system always increases over time and processes occur in a direction that increases total entropy.