Third law of thermodynamics

<p>The third law of thermodynamics states that the <a href="/facts/Entropy/s52IXeFz">entropy</a> of a closed system at <a href="/facts/Thermodynamic_equilibrium/1D7nGm0d">thermodynamic equilibrium</a> approaches a constant value when its temperature approaches <a href="/facts/Absolute_zero/U3UyPl2K">absolute zero</a>. This constant value cannot depend on any other parameters characterizing the system, such as pressure or applied magnetic field. At absolute zero (zero <a href="/facts/Kelvin/E3trzC4C">kelvins</a>) the system must be in a state with the minimum possible energy.
</p><p>Entropy is related to the number of accessible <a href="/facts/Microstate_(statistical_mechanics)/ArXuNn08">microstates</a>, and there is typically one unique state (called the <a href="/facts/Ground_state/ML7cfCug">ground state</a>) with minimum energy. In such a case, the entropy at absolute zero will be exactly zero. If the system does not have a well-defined order (if its order is <a href="/facts/Amorphous_solid/YTIzmrR0">glassy</a>, for example), then there may remain some finite entropy as the system is brought to very low temperatures, either because the system becomes locked into a configuration with non-minimal energy or because the minimum energy state is non-unique. The constant value is called the <a href="/facts/Residual_entropy/5MT7XRII">residual entropy</a> of the system.
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Third law of thermodynamics open-in-new

Third law of thermodynamics