In Problem 12-18 in this section, you used a gamma-phi modeling approach for the pentafluoroethane [R-125] (1) + isobutane (2) system at 30°C. There (if you solved that problem), you realized the benefit of incorporating a gamma-phi   approach (i.e., treating the vapor phase as a real gas rather than an ideal gas) as compared to using modified Raoult’s law.

In this problem repeat the gamma-phi modeling, but treat the vapor-phase as an ideal solution. Here, you are not including the composition effects on the fugacity coefficient, but modeling it as a pure component at the mixture temperature and pressure. Plot both results (the full gamma phi approach from Problem 12-18 and the cur rent approach) as well as the experimental data (as symbols). Additionally, report the following information in tabular form:

∎ The experimental activity coefficients for both approaches 

∎ The ratio of the mixture fugacity coefficient of component i to the saturation fugacity coefficient of component i

What can you conclude about the ideal solution approach to the vapor phase in the context of this problem?

 

Problem 12-18.

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TABLE P12-29 Vapor-liquid equilibrium of R-125 (1) isobutane (2) at 30°C. P(Mpa) 0.4070 0.6900 0.7376 0.8492 0.9714 1.0858 1.2240 1.3412 1.4530 0 0.0816 0.0977 0.1492 0.2085 0.2889 0.4115 0.5371 0.6894 0 Y₁ 0.3998 0.4474 0.5277 0.5977 0.6515 0.7125 0.7611 0.8200