Questions About Vapor Pressure
Multiple-Choice Questions – Vapor Pressure: Characteristics and Lowering
1. What is vapor pressure?
A) The pressure required to boil a liquid
B) The pressure of a vapor in equilibrium with its liquid at a given temperature
C) The pressure exerted by a solid
D) The pressure of air over a surface
E) The pressure after condensation
2. Vapor pressure is a property of which phase equilibrium?
A) Gas–solid
B) Solid–liquid
C) Liquid–vapor
D) Gas–plasma
E) Liquid–solid
3. Which factor most directly affects vapor pressure?
A) Altitude
B) Pressure of the container
C) Temperature
D) Solute concentration
E) Surface area
4. As temperature increases, vapor pressure:
A) Decreases
B) Remains constant
C) Increases
D) Drops to zero
E) Becomes undefined
5. A volatile liquid has:
A) Low vapor pressure
B) High boiling point
C) Strong intermolecular forces
D) High vapor pressure
E) Low surface tension
6. Which of the following will have the highest vapor pressure at the same temperature?
A) Water
B) Mercury
C) Ethanol
D) Glycerol
E) Oil
7. The vapor pressure of a solution is generally ________ than that of a pure solvent.
A) Higher
B) Equal
C) Lower
D) Zero
E) Unpredictable
8. What causes the lowering of vapor pressure in a solution?
A) Increased pressure
B) Decreased volume
C) Addition of a non-volatile solute
D) Heating the solvent
E) Removal of solvent
9. Which law explains vapor pressure lowering in ideal solutions?
A) Boyle's Law
B) Henry's Law
C) Dalton’s Law
D) Charles's Law
E) Raoult’s Law
10. According to Raoult's Law, the vapor pressure of a solution is:
A) Equal to that of the solute
B) Proportional to the solute's mole fraction
C) The sum of solvent and solute vapor pressures
D) Proportional to the solvent’s mole fraction
E) Always lower than 1 atm
11. When a non-volatile solute is added to a solvent, what happens to its boiling point?
A) Increases
B) Decreases
C) Stays the same
D) Falls below 0°C
E) Depends on the container
12. What happens to vapor pressure if you add salt to water?
A) It increases
B) It decreases
C) It remains the same
D) It evaporates faster
E) It becomes equal to atmospheric pressure
13. Vapor pressure lowering is a:
A) Colligative property
B) Physical state
C) Chemical reaction
D) Phase transition
E) Type of solution equilibrium
14. Which of the following is not a factor that lowers vapor pressure?
A) Non-volatile solute
B) Increased solute concentration
C) Higher temperature
D) Strong solute–solvent interactions
E) Decreased mole fraction of solvent
15. The vapor pressure of a solution depends on:
A) Type of solute only
B) Solvent only
C) Amount of solute and solvent
D) Molar mass of solute only
E) External pressure only
16. If the vapor pressure of pure water at 25°C is 23.8 mmHg, what happens when a sugar solution is prepared with it?
A) Vapor pressure increases
B) Vapor pressure remains 23.8 mmHg
C) Vapor pressure becomes zero
D) Vapor pressure decreases
E) Vapor pressure depends only on volume
17. Lowering vapor pressure causes which of the following changes in the boiling point?
A) Decreases it
B) Increases it
C) Eliminates it
D) Has no effect
E) Keeps it constant
18. A higher concentration of solute leads to:
A) Higher vapor pressure
B) Lower vapor pressure
C) More evaporation
D) Higher surface tension
E) Increased condensation
19. Which of the following does not describe a volatile substance?
A) Evaporates easily
B) Has low boiling point
C) Has weak intermolecular forces
D) Has low vapor pressure
E) Can form vapor at room temperature
20. Why is vapor pressure important in cooking at high altitudes?
A) Vapor pressure is higher there
B) Water boils at a higher temperature
C) Cooking time is reduced
D) Lower atmospheric pressure lowers boiling point
E) Water cannot vaporize
Answer Key with Full Explanations
1. B – Vapor pressure is the pressure exerted by vapor in equilibrium with its liquid at a given temperature.
2. C – It occurs at the liquid–vapor equilibrium.
3. C – Temperature is the primary factor affecting vapor pressure.
4. C – As temperature increases, molecules escape more easily, increasing vapor pressure.
5. D – A volatile liquid evaporates easily, meaning it has a high vapor pressure.
6. C – Ethanol is more volatile than water and glycerol, so it has a higher vapor pressure.
7. C – Vapor pressure lowers when solutes are added.
8. C – A non-volatile solute reduces the number of solvent molecules at the surface, lowering vapor pressure.
9. E – Raoult’s Law governs vapor pressure lowering in ideal solutions.
10. D – Raoult’s Law: P_solution = X_solvent × P_pure_solvent.
11. A – Lower vapor pressure means the solution must be heated more to boil.
12. B – Adding salt lowers vapor pressure due to reduced surface solvent particles.
13. A – It is a colligative property, depending on solute amount, not type.
14. C – Higher temperature increases vapor pressure, not lowers it.
15. C – It depends on the ratio of solute to solvent, not just one.
16. D – A sugar solution has lower vapor pressure than pure water.
17. B – Lower vapor pressure requires more heat to reach boiling, raising boiling point.
18. B – More solute means fewer solvent molecules at the surface → lower vapor pressure.
19. D – Volatile substances have high, not low, vapor pressure.
20. D – At higher altitudes, lower atmospheric pressure means water boils at a lower temperature.
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