The Lewis and Randall L-R Fugacity Rule

Example 7.6 In Example 7.5 we estimated the fugacity of methane in a mixture of 78.4 mol% methane, balance n-butane at 1000 psia and 220°F, directly from the measured PvT data. For that example, estimate the values of 4 i and Use these values to evaluate the L-R mle for this example, and to evaluate the relative effects of pure-gas nonideality and of nonideality of mixing. 

In that example, we found directly from the PvT data that for methane 

From Starhng s tables of hydrocarbon properties [3, p. 14] we read that for pure methane at this T and P, fj/P = (f i = 0.954, from which it follows that 

If we wish to use the L-R rule for the -butane, we must estimate the / , for it, not using the observed value of the nonexistent pure vapor at this Tand P. The only practical way is to use some EOS. 

Example 7.7 Estimate the value of / , that -butane would have if it could exist as a gas at 7). = 0.889 and Pr= 1.815, using the little EOS. 

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