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Third Law of Thermodynamics


There are three laws of thermodynamics. The first law of thermodynamics tells about the work and energy. The second law gives the concept of entropy. The third law is in fact more interesting that tells all about the concept of absolute zero. Lets study more about it.

Third  law of thermodynamics definition

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Rudolf Clausius developed the concept of entropy. It is nothing but the dispersal of energy. The greater the dispersal or spreading the larger is the entropy.

The Third Law of Thermodynamics states that,
The entropy of a system approaches a constant value as temperature approaches zero. It states that absolute zero, the lowest possible temperature can never be reached. In short the entropy of a system is zero at absolute zero.

Third law of thermodynamics equation

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The Third Law of Thermodynamics is also called Nernst law given as
$lim_{T\to 0}$ S = 0
If the entropy is zero at temperature T = 0 then the absolute entropy Sab of a substance at temperature Sab of a substance at temperature T and pressure P is given by expression

$S_{ab}$ = $\int_{0}^{T}$ $\frac{(\Delta Q)_rev}{T}$

$\Delta$ Qrev is the amount of heat supplied to the system,
T is the temperature

Third law of thermodynamics examples

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Lets see some examples on third law of thermodynamics:

The lowest possible temperate is absolute zero. There lies a question is "Is it possible to reach it?". In order to cool anything down we need a refrigerator. As the temperature gets colder and colder the refrigerator ability to cool further, its efficiency to get cool gets reduced, eventually comes to zero. You can potentially cool very close to absolute zero but it cant be reached exactly.The last part of heat cant be removed.

Behavior of solid at low temperature
It is difficult to attain absolute zero by the solid. Hence they attain lower temperature but not at absolute zero.