Recently a hard-like equation of state of real fluids has been used to derive an analytical expression of effective pair correlation function at contact, [1]. It has been shown that can be used for prediction of the thermodynamic properties of all kind of fluids, including non-polar, polar, and hydrogen-bonded systems successfully. The analytical expression of free energy of cavity formation, , as an important property of fluids can also be derived by using of the and its derivatives [2]. In this work a new analytical expression introduced for by using of , and used for prediction of the free energy of cavity formation in water. The results are compared with the predictions obtained from computer simulation and analytical expressions of hard sphere fluids as well.
