Fugacity of pure gases

Equation 7-14 is used to calculate the reference state fugacity of liquids. Any equation of state can be used to evaluate ([) . For low to moderate pressures, the virial equation is the simplest to use. The fugacities of pure gases and gas mixtures are needed for estimating many thermodynamic properties, such as entropy, enthalpy, and fluid phase equilibria. For pure gases, the fugacity is... 

Fugacity of Pure Gases. In order to utilize Eq. (3-12) it is necessary to have information on the actual molal volume as a function of the pressure at the temperature in question. The lack of these data limits the utility of this equation. However, it has been found possible to develop correction factors to the perfect-gas law that will apply to almost all gases and gaseous mixtures. One method of representing these deviation factors is to plot the compressibility factor p, which is equal to PV/RT, as a function of the reduced pressure at constant reduced temperature, where reduced pressure Pr is the pressure divided by the critical pressure, and reduced temperature Tr is the absolute temperature divided by the absolute critical temperature. Such a plot is given in Fig. 3-4 similar plots for higher temperatures and pressures are available. 

Example 7.1 shows the calculation of the fugacity of pure gases. 

In current industrial practice, we almost always estimate the fugacity of pure gases from an EOS. For simple estimates, we use a simple EOS the computer programs that compute and use such fugacity data normally use complex EOSs, which are more accurate than simple EOSs like the little EOS. 

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