Which of the following statements is definitely accurate?

The reaction A + B ? C occurs in the vapor phase. It is an endothermic reaction. It is beneficial to carry out the reaction in the presence of liquid water, because C is somewhat soluble in water while A and B are effectively insoluble. The Henry’s Law constant for C in water increases as the temperature increases. We are interested in maximizing the total number of moles of C in the system, regardless of whether the C is in the liquid or vapor phase.
A system initially contains 10 moles each of A and B (vapor) and 100 moles of liquid water. The system is allowed to reach equilibrium at T= 298.15 K and 0.1 MPa. In a separate experiment, the system initially contains 10 moles each of A and B (vapor) and 100 moles of liquid water, and is allowed to reach equilibrium at T= 423.15 K and 0.1 MPa.
A. The system at 298.15 K will have more total moles of C.
B. The system at 423.15 K will have more total moles of C.
C. The system at 298.15 K will have a higher mole fraction of C in the vapor phase and a lower mole fraction of C in the liquid phase than the one at 423.15 K. But it is unclear which will have a larger total number of moles of C.
D. The system at 298.15 K will have a lower mole fraction of C in the vapor phase and a higher mole fraction of C in the liquid phase than the one at 423.15 K. But it is unclear which will have a larger total number of moles of C.
E. None of these is definitely accurate.


A. Incorrect. Consider the effect of increasing the Henry’s Law constant on x, and consider the effect of temperature on K for an endothermic reaction. Then try again.
B. Incorrect. Consider the effect of increasing the Henry’s Law constant on x, and consider the effect of temperature on K for an endothermic reaction. Then try again.
C. Incorrect. Consider the effect of increasing the Henry’s Law constant on x, and consider the effect of temperature on K for an endothermic reaction. Then try again.
D. Incorrect. Lower T means a lower Henry’s Law constant H, which by itself means a higher x (mole fraction of C in the liquid phase).But lower T, for an endothermic reaction, also means a lower equilibrium constant K, and consequently a lower y (mole fraction of C in the vapor phase). Based on all that, D sounds like the correct answer. Is there one more cause-effect relationship you are missing?
E. Correct. For an endothermic reaction, it is clear K will increase as temperature increases, so the value of y will increase at T increases. The effect of changing T on x is less clear. Lower H (at 423.15 K) means higher x, but higher y (at 423.15 K) also means higher x, according to Henry’s Law. Thus it is impossible to say, from the given information, which system has a higher mole fraction of C in the liquid phase. Without knowing the specific values of Henry’s Law constant and K at 423.15 K and 423.15 K, one cannot say A, B, C or D is absolutely true.
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