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Vapor-Liquid Equilibrium
GATE 2015
Hard
A binary mixture forms an azeotrope at 130°C, x1=0.3. lnγ1=Ax2², lnγ2=Ax1². Fugacity coefficients=0.9 for both at the azeotrope. P1sat=70bar, P2sat=30bar. The total pressure (bar), rounded to 2 decimal places, is
27.55 bar(± 1 accepted)
Explanation
At azeotrope, γ1P1sat=γ2P2sat (φ's cancel, equal). ln(γ1/γ2)=A(0.49−0.09)=ln(30/70) ⟹ A=−2.118. γ1=e^(−1.038)=0.354. P=γ1P1sat/φ1=0.354×70/0.9=27.55 bar.
Source: GATE CH 2015 (2015)
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