Berthelot equation of state: Difference between revisions

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:<math>\frac{p_cv_c}{RT_c} = \frac{3}{8} = 0.375 </math>  
:<math>Z_c = \frac{p_cv_c}{RT_c} = \frac{3}{8} = 0.375 </math>  




where <math>p</math> is the [[pressure]], <math>T</math> is the [[temperature]] and <math>R</math> is the [[molar gas constant]]. <math>T_c</math> is the [[critical points | critical]] temperature, <math>p_c</math> is the pressure and <math>v_c</math> is the volume at the critical point.
where <math>p</math> is the [[pressure]], <math>T</math> is the [[temperature]] and <math>R</math> is the [[molar gas constant]]. <math>T_c</math> is the [[critical points | critical]] temperature, <math>p_c</math> is the pressure and <math>v_c</math> is the volume at the critical point.
==Low pressure variant==
==Low pressure variant==
Berthelot also proposed an [[Equations of state |equation of state]] for use at low pressures:
Berthelot also proposed an [[Equations of state |equation of state]] for use at low pressures{{reference needed}}:




:<math>p = \frac{RT}{v} \left( 1 + \frac{9}{128} \frac{pT_c}{p_c T} \left( 1- \frac{6T_c^2}{T^2} \right)  \right)</math>  
:<math>p = \frac{RT}{v} \left( 1 + \frac{9}{128} \frac{pT_c}{p_c T} \left( 1- \frac{6T_c^2}{T^2} \right)  \right)</math>
 
==References==
==References==
<references/>
<references/>
[[category: equations of state]]
[[category: equations of state]]

Latest revision as of 13:31, 8 January 2014

The Berthelot equation of state [1][2] can be written as

RT=(p+aTv2)(v−b).

At the critical point one has ∂p∂v|T=Tc=0, and ∂2p∂v2|T=Tc=0,

which leads to (Eqs. 4.1 - 4.3 [3][4])


a=3Tcpcvc2


b=vc3

and giving a critical compressibility factor of


Zc=pcvcRTc=38=0.375


where p is the pressure, T is the temperature and R is the molar gas constant. Tc is the critical temperature, pc is the pressure and vc is the volume at the critical point.

Low pressure variant[edit]

Berthelot also proposed an equation of state for use at low pressures[?]


p=RTv(1+9128pTcpcT(1−6Tc2T2))

References[edit]