Difference between revisions of "Third law of thermodynamics"

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The '''third law of thermodynamics''' (or '''Nernst's theorem''' after the experimental work of Walther Nernst) states that the [[entropy]] of a system approaches a minimum (that of its ground state) as one approaches the [[temperature]] of absolute zero. One can write
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The '''third law of thermodynamics''' (or '''Nernst's theorem''' after the experimental work of Walther Nernst in 1906 <ref>[http://gdz.sub.uni-goettingen.de/dms/load/img/?PPN=PPN252457811_1906 W. Nernst "Ueber die Berechnung chemischer Gleichgewichte aus thermischen Messungen" Königliche Gesellschaft der Wissenschaften zu Göttingen Mathematisch-physikalische Klasse. Nachrichten, pp. 1-40 (1906)]</ref>) states that the [[entropy]] of a system approaches a minimum (that of its ground state) as one approaches the [[temperature]] of absolute zero. One can write
  
 
:<math>\lim_{T \rightarrow 0} \frac{S(T)}{N} = 0</math>
 
:<math>\lim_{T \rightarrow 0} \frac{S(T)}{N} = 0</math>
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:<math>\alpha := \frac{1}{V} \left. \frac{\partial V}{\partial T} \right\vert_p = -\frac{1}{V} \left. \frac{\partial S}{\partial p} \right\vert_T \rightarrow 0</math>
 
:<math>\alpha := \frac{1}{V} \left. \frac{\partial V}{\partial T} \right\vert_p = -\frac{1}{V} \left. \frac{\partial S}{\partial p} \right\vert_T \rightarrow 0</math>
 
==References==
 
==References==
#[http://dx.doi.org/10.1088/0305-4470/22/1/021 P. T. Landsberg "A comment on Nernst's theorem", Journal of Physics A: Mathematical and General '''22''' pp. 139-141 (1989)]
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<references/>
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;Related reading
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*[http://dx.doi.org/10.1088/0305-4470/22/1/021 P. T. Landsberg "A comment on Nernst's theorem", Journal of Physics A: Mathematical and General '''22''' pp. 139-141 (1989)]
 
[[category: classical thermodynamics]]
 
[[category: classical thermodynamics]]
 
[[category: quantum mechanics]]
 
[[category: quantum mechanics]]

Revision as of 16:11, 13 January 2012

The third law of thermodynamics (or Nernst's theorem after the experimental work of Walther Nernst in 1906 [1]) states that the entropy of a system approaches a minimum (that of its ground state) as one approaches the temperature of absolute zero. One can write

\lim_{T \rightarrow 0} \frac{S(T)}{N} = 0

where N is the number of particles. Note that there are systems whose ground state entropy is not zero, for example metastable states or glasses, or systems with weakly or non-coupled spins that are not subject to an ordering field.

Implications

The heat capacity (for either pressure or volume) tends to zero as one approaches absolute zero. From

C_{p,V}(T)= T \left. \frac{\partial S}{\partial T} \right\vert_{p,V}

one has

S(T) - S(0) = \int_0^x \frac{C_{p,V}(T)}{T} ~\mathrm{d}T

thus C \rightarrow 0 as T \rightarrow 0, otherwise the integrand would become infinite.

Similarly for the thermal expansion coefficient

\alpha := \frac{1}{V} \left. \frac{\partial V}{\partial T} \right\vert_p = -\frac{1}{V} \left. \frac{\partial S}{\partial p} \right\vert_T \rightarrow 0

References

Related reading