[birdycofir]

Hi, I'm a 2nd year Chemical Engineering student and I was stuck on this question. The question is on the left and the solution is on the right.



1. What is the difference between P_j and P_c,j? What is the relevance of the j?

2. What is χ_j? I'm guessing it's mole fraction.

3. In the solution, why is temperature assumed to be 320K?

[mjc123]

1. j is the component index; j = h for heptane and o for octane. You have to calculate P separately for each component. P_j is the vapour pressure of component j; P_c,j is (I'm assuming) the critical pressure of component j.

2. χ_j (on the LHS) is not mole fraction. It is defined for you. On the RHS, x_j would appear to be mole fraction of j in the liquid, and y_j the mole fraction in the vapour.

3. It is just a starting point. You are told to adjust T until y_o + y_h = 1.