A stream consisting of 48.9 mole% benzene (B) and 51.1% toluene (T) is fed at a constant rate to a process unit that produces two product streams, one a vapor and the other a liquid. The vapor flow rate is initially zero and asymptotically approaches one third of the molar flow rate of the feed stream. Throughout this entire period, no material accumulates in the unit. When the vapor flow rate has become constant, the liquid is analyzed and found to be 28.0 mole% benzene. Required:
How would you expect the vapor flow rate to vary with time?