page_title: Real gas
section_title: Wohl model
hierarchical_section_title: Real gas / Models / Wohl model
caption_attribution_description: English: Isotherm (V_r-&gt;p_r) at critical temperature for Wohl model, van der Waals model and ideal gas model
context_page_description: Real gases are nonideal gases whose molecules occupy space and have interactions; consequently, they do not adhere to the ideal gas law.
  To understand the behaviour of real gases, the following must be taken into account:
  compressibility effects;
  variable specific heat capacity;
  van der Waals forces;
  non-equilibrium thermodynamic effects;
  issues with molecular dissociation and elementary reactions with variable composition
  For most applications, such a detailed analysis is unnecessary, and the ideal gas approximation can be used with reasonable accuracy. On the other hand, real-gas models have to be used near the condensation point of gases, near critical points, at very high pressures, to explain the Joule–Thomson effect and in other less usual cases. The deviation from ideality can be described by the compressibility factor Z.
context_section_description: The Wohl equation (named after A. Wohl) is formulated in terms of critical values, making it useful when real gas constants are not available, but it cannot be used for high densities, as for example the critical isotherm shows a drastic decrease of pressure when the volume is contracted beyond the critical volume.
  or:
  or, alternatively:
  where
   with 
  , where  are (respectively) the molar volume, the pressure and the temperature at the critical point.
  And with the reduced properties  one can write the first equation in the reduced form:
caption: Isotherm (V/V0->p_r) at critical temperature for Wohl model, van der Waals model and ideal gas model (with V0=RTc/pc)
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