Vapor-Liquid Equilibrium for Non-Ideal Solutions: Example Problems

Try to solve these problems before watching the solutions in the screencasts.

Example Problem 1

A vapor-phase mixture of components 1 and 2 is compressed at fixed temperature until the vapor completely condenses. The vapor contains 30 mol% component 1 and 70 mol% component 2. The saturation pressures for components 1 and 2 at the temperature of the system are 0.82 and 1.93 bar, respectively. The bubble pressure of a 50:50 mixture of components 1 and 2 is 1.08 bar.

  •  Estimate the pressure require to completely liquify the 30:70 mixture, assuming that the excess Gibbs free energy of the liquid is well-modeled by the one-parameter Margules equation.
  •  Would the required pressure to liquify the mixture be higher or lower if components 1 and 2 formed an ideal solution?
Example Problem 2

Calculate the bubble pressure of a binary system. The mole fraction of component 1 in the liquid phase is 0.40 and the pressure is 70 kPa. The saturation pressures: 

\[P_1^{sat}\,=\, exp\left(14.3\,-\,\frac{2940}{T+224}\right) \;\;\;\;\;\;\;\; P_2^{sat}\,=\,exp\left(14.2-\frac{2975}{T+209}\right)\]

\(T\) is in \(^oC\), \(P\) is in kPa