The Third Law of Thermodynamics states that as the temperature of a system approaches absolute zero (0 Kelvin or –273.15 °C), the entropy (disorder or randomness) of a perfect crystalline substance approaches zero.
In simple words:
- At absolute zero, a perfectly ordered crystal has only one possible arrangement of its particles, so there is no randomness.
- It is impossible to reach absolute zero in a finite number of steps, meaning we can get close to it but never actually achieve it.
Key points:
- Entropy at absolute zero = 0 (for a perfect crystal).
- This law sets a reference point for calculating absolute entropy of substances.
- It explains why substances behave differently at very low temperatures, such as superconductivity or superfluidity.
- It shows a fundamental limit to how cold something can get.
Examples:
- Liquid helium shows strange behavior near absolute zero, like flowing without friction.
- In cryogenics, scientists use this principle to cool materials for superconductors and quantum experiments.
In short: The Third Law helps us understand the behavior of matter at extremely low temperatures and gives a baseline for entropy.