Q25: Which of the following would be true for the FEED stream in the table?
A. G1, molecular weight > G2, molecular weight
B. L1, vapour pressure > L2, vapour pressure
C. G1, molecular weight < G2, molecular weight
D. L1, vapour pressure < L2, vapour pressure
E. Information not sufficient for vapour pressure comparison
B & C; At higher pressure, relatively heaviour ends will get dissolved in L1 (only to come out with G2 at lower pressure in stage2, while G1 will mainly consist of the lighter components that would remain in the vapour space even at higher pressure). Since Lights in L1 will flash to G2 at lower pressure, L2 will be heavier than L1. Since no separate gas stream is mixing up in Feed to first Separator, the pressure in there is same as the vapour pressure of liquid in equilibrium (therefore, vp1>vp2).
Q26. Four people need to cross a rickety bridge at night. Unfortunately, they have only one torch and the bridge is too dangerous to cross without one. The bridge is only strong enough to support two people at a time. Not all people take the same time to cross the bridge. Times for different persons are 1 min, 2 mins, 7 mins and 10 mins. What is the shortest time needed for all four of them to cross the bridge?
1 and 2 cross first
2 comes back with torch
Now 7 and 10 go across
1 comes back with torch
1 and 2 go across
Total time = 2 + 2 + 10 + 1 + 2 = 17 mins