The Fugacity of Pure Liquids and Solids

In principle, we could compute the fugacity of pure liquids and solids the same way we computed that of gases. This is impractical, however, so we use other methods. The reason is that the molar volume v of liquids and solids is so small that the volume residual a is practically the same as the ideal gas volume. 

Example 7.2 Estimate the compressibility factor z and the volume residual a for liquid water at 100°F and 1 psi. 

From the steam table, the specific volume of water at 101.7°F 100°F and 1 psia is 0.016136ftVlbm = 0.290 ft /lbmol and we compute that 

This value of a is large enough that if we were to use it in Eq. 7.10 we would have a very large exponential, which would be very sensitive to round-off errors and hence very unreliable. (If we had perfect liquid PvT data, we could use it. We never have perfect data.) So we proceed a different way. 

We also know from Eq. 7.5 that/c=/, = 0.95 psia. To find fd we use the integrated form of Eq. 7.7 

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