Additive polynomial

2013-11-21T20:26:33Z

110.20.130.141: /* See also */ added extra link

{{Refimprove|article|date=September 2009}}
The '''Sackur–Tetrode equation''' is an expression for the [[entropy]] of a [[monatomic]] classical [[ideal gas]] which incorporates quantum considerations which give a more detailed description of its regime of validity.

The Sackur–Tetrode equation is named for [[Hugo Martin Tetrode]]<ref>H. Tetrode (1912) "Die chemische Konstante der Gase und das elementare Wirkungsquantum" (The chemical constant of gases and the elementary quantum of action), ''Annalen der Physik'' '''38''': 434 - 442. See also: H. Tetrode (1912) [http://onlinelibrary.wiley.com/doi/10.1002/andp.19123441112/pdf "Berichtigung zu meiner Arbeit: "Die chemische Konstante der Gase und das elementare Wirkungsquantum" "] (Correction to my work: "The chemical constant of gases and the elementary quantum of action"), ''Annalen der Physik'' '''39''': 255 - 256.</ref> (1895–1931) and [[Otto Sackur]]<ref>Sackur published his findings in the following series of papers:
# O. Sackur (1911) "Die Anwendung der kinetischen Theorie der Gase auf chemische Probleme" (The application of the kinetic theory of gases to chemical problems), ''Annalen der Physik'', '''36''': 958 - 980.
# O. Sackur, "Die Bedeutung des elementaren Wirkungsquantums für die Gastheorie und die Berechnung der chemischen Konstanten" (The significance of the elementary quantum of action to gas theory and the calculation of the chemical constant), ''Festschrift W. Nernst zu seinem 25jährigen Doktorjubiläum gewidmet von seinen Schülern'' (Halle an der Salle, Germany: Wilhelm Knapp, 1912), pages 405 - 423.
# O. Sackur (1913) "Die universelle Bedeutung des sog. elementaren Wirkungsquantums" (The universal significance of the so-called elementary quantum of action), ''Annalen der Physik'' '''40''': 67 - 86.</ref> (1880–1914), who developed it independently as a solution of Boltzmann's gas statistics and entropy equations, at about the same time in 1912.

==Formula==
The Sackur–Tetrode equation is written:

:<math>
S = k N \ln
\left[ \left(\frac VN\right) \left(\frac UN \right)^{\frac 32}\right]+
{\frac 32}kN\left( {\frac 53}+ \ln\frac{4\pi m}{3h^2}\right)
</math>

where ''V'' is the volume of the gas, ''N'' is the number of particles in the gas, ''U'' is the internal energy of the gas, ''k'' is [[Boltzmann's constant]], ''m'' is the mass of a gas particle, ''h'' is [[Planck's constant]] and ln() is the [[natural logarithm]]. See [[Gibbs paradox]] for a derivation of the Sackur–Tetrode equation. See also the [[ideal gas]] article for the constraints placed upon the entropy of an ideal gas by thermodynamics alone.

The Sackur–Tetrode equation can also be conveniently expressed in terms of the [[thermal wavelength]] <math> \Lambda </math>.

:<math>
\frac{S}{kN} = \ln\left[\frac{V}{N\Lambda^3}\right]+\frac{5}{2}.
</math>

Note that the assumption was made that the gas is in the classical regime, and is described by [[Maxwell–Boltzmann statistics]] (with "correct Boltzmann counting"). From the definition of the [[Thermal de Broglie wavelength|thermal wavelength]], this means the Sackur–Tetrode equation is only valid for

:<math>\frac{V}{N\Lambda^3}\gg 1</math>

and in fact, the entropy predicted by the Sackur–Tetrode equation approaches negative infinity as the temperature approaches zero.

==Sackur–Tetrode constant==
The '''Sackur–Tetrode constant''', written ''S''0/''R'', is equal to ''S/kN'' evaluated at a temperature of ''T'' = 1 [[kelvin]], at [[Standard state|standard pressure]] (100 kPa or 101.325 kPa, to be specified), for one [[mole (unit)|mole]] of an ideal gas composed of particles of mass equal to one [[atomic mass unit]] (''m''u = {{nowrap|1.660 538 782(83){{e|−27}} kg}}). Its 2006 [[CODATA]] recommended value is:<ref>{{CODATA2006|url=http://physics.nist.gov/cgi-bin/cuu/Value?s0sr}}</ref>
:''S''0/''R'' = −1.151 7047(44) for ''p''<s>o</s> = 100 kPa
:''S''0/''R'' = −1.164 8677(44) for ''p''<s>o</s> = 101.325 kPa.

==Interpretation of the equation through information theory==

In addition to using the [[entropy|thermodynamic perspective of entropy]] the tools of [[information theory]] can be used to provide an [[Entropy (information theory)|information perspective of entropy]]. The physical chemist [[Arieh Ben-Naim]] rederived the Sackur–Tetrode equation for entropy in terms of information theory, and in doing so he tied in well known concepts from [[modern physics]]. He showed the equation to consist of the sum of four entropies (missing information) due to positional uncertainty, momenta uncertainty, the quantum mechanical [[uncertainty principle]] and the [[indistinguishability]] of the particles.<ref>{{cite book |title=A Farewell to Entropy: Statistical Thermodynamics Based on Information |last=Ben-Naim |first=Arieh |year=2008 |publisher=World Scientific Publishing Company |isbn=978-981-270-706-2 |url=http://books.google.com/?id=gnRckGEB3uQC&dq=A+farewell+to+entropy:+statistical+thermodynamics+based+on+information&printsec=frontcover&q= |accessdate=2009-11-28}}</ref>

Neglecting k, the Sackur–Tetrode equation is then given as:

:<math>
S = \left[ N\ln V\right] + \left[\frac 32 N\ln\left(2\pi e m T\right)\right] + \left[ -3N\ln h\right] + \left[-\ln N! \right]
≈ N \ln \left[\frac{V}{N} \left(\frac{2\pi m T}{h^2}\right)^{\frac 32}\right] + \frac 52 N
</math>

The derivation uses the Stirling approximation, <math>\ln N! ≈ N \ln N - N</math>.

==References==
{{reflist}}

{{Statistical mechanics topics}}

{{DEFAULTSORT:Sackur-Tetrode equation}}
[[Category:Equations of state]]
[[Category:Ideal gas]]
[[Category:Thermodynamic entropy]]

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Additive polynomial