Which of the following is NOT true?

Question

A reaction A+B?C occurs in the liquid phase. A vessel contains a liquid at P = 1 MPa and T = 298.15 K. The vessel initially contains 10 moles of A and 10 moles of B, but the reaction is allowed to reach equilibrium at P = 1 MPa and T = 298.15 K. After the reaction reaches equilibrium, the pressure is reduced isothermally until it reaches 0.13 MPa, at which point the first bubble of vapor forms. The liquid at this point is 39 mol% A, 39 mol% B and 22 mol% C. The first bubble of vapor is 52 mol% A, 40 mol% B and 8 mol% C.
A. If the pressure is further decreased isothermally, the total number of moles of C in the vessel will decrease.
B. The vapor pressure of A at this temperature is about 0.173 MPa, assuming the liquid is an ideal solution.
C. The equilibrium constant of the liquid phase reaction is 1.88, if the liquid is an ideal solution.
D. The equilibrium constant for the reaction is 1.45, if the liquid is an ideal solution.
E. If the vapor pressure of C is above 50kPa at this temperature, then the activity coefficient of C must be below 1.

Answer 1

A. Incorrect. This is true. The reduction in pressure will cause A and B to evaporate faster than C, which will shift the liquid phase reaction back to the left.
B. Incorrect. This is true. If you solve Raoult’s law for PAsat this is the result, but Raoult’s Law assumes the liquid is an ideal solution. It also assumes the vapor is an ideal gas, but departure from ideal gas behavior is probably small at this pressure.
C. Correct.This is a wrong value of the equilibrium constant.
D. Incorrect. This is a correct equilibrium constant for the liquid phase reaction.
E. Incorrect. This is true. The vapor pressure of C according to Raoult’s Law is 47 kPa. Thus, if the true vapor pressure is above 50kPa, then in order for modified Raoult’s Law to hold, the activity coefficient of C must be below 1.
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