Questions on Vapor Pressure
20 Multiple-Choice Questions on Vapor Pressure
1. What is vapor pressure?
A) The pressure required to boil a liquid
B) The pressure of a gas when it liquefies
C) The pressure exerted by vapor in equilibrium with its liquid
D) The total atmospheric pressure at sea level
E) The pressure applied by solids in a container
2. At equilibrium, vapor pressure depends on:
A) The volume of the container
B) The color of the liquid
C) The temperature of the system
D) The amount of vapor present
E) The molecular mass of the container
3. When the temperature of a liquid increases, its vapor pressure:
A) Decreases
B) Increases
C) Remains the same
D) Drops to zero
E) First increases, then decreases
4. A liquid boils when its vapor pressure is:
A) Less than atmospheric pressure
B) Greater than atmospheric pressure
C) Equal to atmospheric pressure
D) Zero
E) Double the atmospheric pressure
5. Which substance would have the highest vapor pressure at the same temperature?
A) Water
B) Ethanol
C) Acetone
D) Glycerol
E) Olive oil
6. A volatile substance:
A) Has a very low vapor pressure
B) Is always toxic
C) Has a high vapor pressure
D) Never evaporates
E) Cannot form vapor
7. What causes a substance to exert vapor pressure?
A) Attraction of vapor molecules to each other
B) Intermolecular collisions in solids
C) Kinetic energy of molecules escaping from the liquid
D) The density of the liquid
E) External pressure pushing molecules down
8. At higher altitudes (lower atmospheric pressure), liquids boil:
A) At higher vapor pressure
B) At lower temperature
C) At higher temperature
D) Only under vacuum
E) Without evaporating
9. When a liquid is placed in a closed container, its vapor pressure:
A) Remains zero
B) Continues to increase indefinitely
C) Increases then stabilizes at equilibrium
D) Equals atmospheric pressure
E) Drops immediately
10. The Clausius-Clapeyron equation relates vapor pressure to:
A) Temperature and density
B) Temperature and viscosity
C) Temperature and molar volume
D) Temperature and enthalpy of vaporization
E) Temperature and refractive index
11. Weak intermolecular forces result in:
A) Low vapor pressure
B) High vapor pressure
C) No evaporation
D) High melting point
E) High viscosity
12. Which of the following does not affect vapor pressure directly?
A) Temperature
B) Type of liquid
C) Atmospheric pressure
D) Intermolecular forces
E) Enthalpy of vaporization
13. Vapor pressure is a measure of:
A) The amount of solute in a solvent
B) The strength of gravity on vapor molecules
C) The equilibrium between evaporation and condensation
D) The solubility of a gas in water
E) The molecular weight of a compound
14. At 25°C, which would you expect to have the lowest vapor pressure?
A) Acetone
B) Ethanol
C) Water
D) Glycerol
E) Diethyl ether
15. A liquid with strong hydrogen bonds will generally have:
A) Higher vapor pressure
B) Lower vapor pressure
C) Constant vapor pressure
D) Vapor pressure equal to atmospheric pressure
E) No vapor pressure
16. At the boiling point of a liquid, the vapor pressure:
A) Is zero
B) Is less than external pressure
C) Is equal to external pressure
D) Is unrelated to temperature
E) Becomes negative
17. What happens to vapor pressure if a non-volatile solute is added to a solvent?
A) Increases
B) Decreases
C) Remains the same
D) Doubles
E) Equals that of the solute
18. Raoult’s Law applies to:
A) Ideal gases only
B) Electrolytic solutions
C) Solubility of solids
D) Vapor pressure of solutions
E) Surface tension of liquids
19. Dynamic equilibrium in a closed container means:
A) No molecules move
B) Condensation stops
C) Evaporation is faster than condensation
D) Rate of evaporation equals rate of condensation
E) Temperature decreases continuously
20. Which property of a liquid most directly influences its vapor pressure?
A) Color
B) pH
C) Intermolecular forces
D) Electrical conductivity
E) Surface tension
Answers with Explanations
1. C – Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid.
2. C – Vapor pressure depends on temperature; higher temperature increases kinetic energy.
3. B – As temperature rises, more molecules escape the liquid, raising vapor pressure.
4. C – Boiling occurs when vapor pressure equals atmospheric pressure.
5. C – Acetone is volatile and has weak intermolecular forces, so high vapor pressure.
6. C – Volatile substances evaporate readily, meaning they have high vapor pressure.
7. C – Molecules with enough kinetic energy escape from liquid to vapor phase.
8. B – At high altitudes, lower atmospheric pressure allows boiling at lower temperatures.
9. C – In a closed system, vapor pressure increases until dynamic equilibrium is reached.
10. D – The Clausius-Clapeyron equation links vapor pressure with enthalpy of vaporization and temperature.
11. B – Weak intermolecular forces make it easier for molecules to escape, increasing vapor pressure.
12. C – Atmospheric pressure affects boiling point, not vapor pressure in a closed system.
13. C – Vapor pressure reflects balance between evaporation and condensation in a closed system.
14. D – Glycerol has strong hydrogen bonding and low volatility, thus lowest vapor pressure.
15. B – Strong hydrogen bonding resists evaporation, resulting in low vapor pressure.
16. C – At boiling point, vapor pressure equals external pressure, allowing bubbling throughout.
17. B – A non-volatile solute reduces the solvent's vapor pressure (Raoult’s Law).
18. D – Raoult’s Law quantifies how vapor pressure decreases with addition of a solute.
19. D – In dynamic equilibrium, evaporation rate equals condensation rate.
20. C – Intermolecular forces determine how easily molecules can escape into vapor.
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