Third Law of Thermodynamics
Definition and meaning of Third Law of Thermodynamics in chemistry.
The Third Law of Thermodynamics states that the absolute entropy of a perfect crystal of a pure substance approaches exactly zero as the absolute temperature approaches zero Kelvin. It establishes a fundamental baseline reference point for the accurate determination of absolute entropy values for all substances.
In more detail
At absolute zero, all thermal motion of atoms and molecules theoretically ceases completely. In a perfect, defect-free crystal, the constituent particles are arranged in one unique, perfectly ordered ground state. Since entropy is a measure of the total number of possible microstates in a given system, having a single microstate means the entropy is zero. This law is crucial for calculating the absolute standard entropies of substances at higher temperatures by continuously integrating their heat capacities from zero Kelvin upwards.
Key facts
| Field | Physical Chemistry |
|---|---|
| Formula | CO |
| Principle | Entropy of a perfect crystal at 0 Kelvin is zero |
| Significance | Provides an absolute baseline reference for entropy calculations |
The absolute entropy of a perfectly ordered crystal of solid carbon monoxide (CO) would approach zero at 0 Kelvin, although in actual practice, it often freezes in multiple orientations resulting in slight residual entropy.
Frequently asked questions
Can absolute zero ever be truly reached in a laboratory setting?
According to the fundamental principles of thermodynamics, absolute zero cannot be attained in a finite number of physical steps, though researchers have successfully cooled substances to tiny fractions of a degree above 0 Kelvin.