The figure below provides a Pxy diagram for the R-134a (1) + R-245fa (2) system at 293.15 K. Which of the following is true?

Question

A. The vapor pressure of the R-134a is less than that of R-245fa at 293.15 K.

B. At 293.15 K and 0.4 MPa, an equimolar mixture of this system will exist in two phases (liquid and vapor).

C. At 293.15 K and 0.3 MPa, a mixture that contains 20 moles of R-134a and 80 moles of R-245fa will exist in a single liquid phase.

D. At 293.15 K and 0.2 MPa, a mixture that contains 80 moles of R-134a and 20 moles of R-245fa will exist in a single liquid phase.

E. None of the above are true.

Answer 1

A. Incorrect. This is backwards. Remember that, although the abscissa is labeled in R-134a, at x = 0, none is present and we read the vapor pressure of the other component (R-245fa).
B. Incorrect. Find the point on the graph indicated; it is above the bubble-point curve and, thus, will exist as one liquid phase.
C. Correct. This point is above the bubble-point curve on this Pxy plot, so we know it will exist as one liquid phase.
D. Incorrect. This point is under the dew-point curve, so we will have one vapor phase.
E. Incorrect. One of the statements is true.