Determine the pressure of the system and the equilibrium constant for the reaction.

Question

A reaction A+B?C+D occurs in the liquid phase at 298.15 K. A vapor phase is also present, but no reaction occurs in the vapor phase. The liquid is an ideal solution and the vapor is an ideal gas. Vapor pressures are 0.12 MPa for compound A, 80kPa for compound B, 0.15 MPa for compound C and 70kPa for compound D. At equilibrium the liquid phase consists of 36 mol% A, 33 mol% B, 11 mol% C and 20 mol% D.
A. P = 0.42MPa; KT = 5.4
B. P = 0.42 MPa; KT = 0.185
C. P = 0.1 MPa; KT = 5.4
D. P = 0.1 MPa; KT = 0.185
E. Solution not possible with information given

Answer 1

A. Incorrect. You cannot simply sum the vapor pressures to get the total pressure; you need to apply an equilibrium model.
B. Incorrect. You cannot simply sum the vapor pressures to get the total pressure; you need to apply an equilibrium model.
C. Incorrect. The pressure is correct, but the KT is not. Try again after reviewing Example 14-4.
D. Correct. Using Raoult’s Law, you obtain the total pressure. Using the definition of equilibrium, you obtain KT.
E. Incorrect. There is enough information given to make assumptions and solve for both.