Which of the following would you NOT expect to increase the total number of moles of C?

Question

The reaction A + B ? C occurs in the vapor phase. It is an exothermic 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. Increasing the pressure at constant temperature.
B. Increasing the number of moles of water while leaving P and T constant.
C. Increasing the temperature at constant pressure.
D. Decreasing the temperature at constant pressure.
E. It is impossible to answer the question without specific values of H and K.

Answer 1

A. Incorrect. This will increase the number of moles of C two ways—it will shift the equilibrium of the vapor phase reaction to the right, and it will also increase the number of moles of C in the liquid phase, according to Henry’s Law.
B. Incorrect. The mole fractions of all compounds in each phase are fixed by equilibrium relationships. Increasing the mass of the liquid phase will mean more C is dissolved in the liquid on an absolute basis.
C. Correct. Increasing the temperature will both lower K (leading to less C in the vapor phase) and increase H (leading to less C in the liquid phase).
D. Incorrect. Decreasing the temperature will both increase K for this exothermic reaction and decrease the Henry’s Law constant. Thus the mole fraction of C in both phases will increase.
E. Incorrect. This question can be answered accurately in a qualitative sense.