关键词: equation of state;saturated vapor pressure;saturatedliquid volume

Abstract: A new approach to the investigation of vdW type of equations of state (EOS)is developed by
embedding a vapor pressure equation and a saturated liquidvolume equation into vdW type
EOS, which results in a new function As(T). The As(T)possesses the properties of an
attractive parameter A(T), and if an EOS isaccurate in the whole PVT space, then its
numerical value equals A(T). As auseful tool for investigating EOS, the As(T) has been used
to makecomparisonsamong RKS, PRSVII, PT and ALS EOS, and to indicate where the
shortcomingsof the EOS are coming from. Based on the As(T), a possible way to develop a
realpredictive equation of state is also suggested.

Key words: equation of state, saturated vapor pressure, saturatedliquid volume