Multiple Choice
What is it called when plants give off water vapor as a waste product?
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14. Solutions
Vapor Pressure Lowering (Raoult's Law)
Multiple Choice
Which of the following will increase the vapor pressure of a liquid according to Raoult's Law?
A
Decreasing the concentration of a nonvolatile solute in the liquid
B
Adding more nonvolatile solute to the liquid
C
Lowering the temperature of the liquid
D
Increasing the pressure above the liquid
Verified step by step guidance1
Recall Raoult's Law, which states that the vapor pressure of a solvent in a solution is proportional to the mole fraction of the solvent: \(P_{\text{solution}} = X_{\text{solvent}} \times P^\circ_{\text{solvent}}\), where \(P^\circ_{\text{solvent}}\) is the vapor pressure of the pure solvent.
Understand that adding a nonvolatile solute decreases the mole fraction of the solvent (\(X_{\text{solvent}}\)), which lowers the vapor pressure of the solution compared to the pure solvent.
Recognize that decreasing the concentration of the nonvolatile solute increases the mole fraction of the solvent, thus increasing the vapor pressure according to Raoult's Law.
Note that lowering the temperature decreases the vapor pressure of the pure solvent itself, so it does not increase vapor pressure.
Understand that increasing the pressure above the liquid does not affect the vapor pressure of the liquid directly, as vapor pressure depends on temperature and composition, not external pressure.
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