Background: The liquid molar volume (V) and the heat of vaporization (ΔHVAP) of four fatty acids (n-Heptanoic acid, Hexadecanoic acid, n-Hexanoic acid and n-
Dodecanoic acid) have been estimated.
Objective: This paper aims to calculate the liquid molar volume and the heat of vaporization
of four fatty acids under the critical point using two traditional equations of state:
Peng-Robinson (PR)  and Soave-Redlich-Kwong.
Methods: The area rules method applicable to obtaining the saturation pressure of the
compounds has been used. The properties of the acids investigated in this work have been
compared with those provided by literature. For molar volumes, the equations of state have
given improved predictions when compared to traditional equations such as Rackett equation
and so on. According to the vapor enthalpy calculations, no reference value was required.
Results: In general, the Clausius-Clapeyron equation provides a better estimation of the
vaporization enthalpy of fatty acids when Soave-Redlich-Kwong (SRK) equation was
used. The heat of vaporization for fatty acids can be calculated with good reliability in
comparison with the Watson equation if suitable equation of state is used.
Conclusion: Accurate results for heat of vaporization can be reached in comparison with
the Watson equation if the reliable equation of state is used.