Questions about Heats of Vaporization and Condensation
Multiple-Choice Questions: Heats of Vaporization and Condensation
1. What does the heat of vaporization represent?
A) The energy required to freeze a liquid
B) The energy needed to melt a solid
C) The energy required to convert a liquid into a gas
D) The energy released when a solid turns into a liquid
E) The energy absorbed during condensation
2. Which of the following describes the heat of condensation?
A) Energy required to change solid to gas
B) Energy absorbed during boiling
C) Energy released when gas turns into liquid
D) Energy required for sublimation
E) Energy used to raise temperature of liquid
3. What is the approximate heat of vaporization of water at 100°C?
A) 334 J/g
B) 4180 J/g
C) 100 J/g
D) 2260 J/g
E) 500 J/g
4. When water condenses, the heat of vaporization is:
A) Absorbed
B) Destroyed
C) Released
D) Doubled
E) Divided
5. Which equation is used to calculate energy involved in vaporization or condensation?
A) Q = mcΔT
B) Q = mLv
C) Q = PΔV
D) Q = nRT
E) Q = mLf
6. If 5 g of water vapor condenses, how much energy is released? (Use 2260 J/g)
A) 1130 J
B) 11300 J
C) 22600 J
D) 4520 J
E) 226 J
7. In vaporization, temperature remains constant because:
A) No heat is used
B) Heat raises kinetic energy
C) Heat is stored for later use
D) Heat is used to overcome intermolecular forces
E) Heat decreases during boiling
8. What occurs at the molecular level during vaporization?
A) Molecules form ionic bonds
B) Molecules absorb energy and move freely
C) Molecules slow down
D) Molecules freeze
E) Molecules lose mass
9. During condensation, the process is:
A) Endothermic
B) Isothermal
C) Exothermic
D) Adiabatic
E) Radioactive
10. Why is more energy required to vaporize water than to melt ice?
A) Gas molecules are heavier
B) Vaporization breaks more intermolecular forces
C) Ice has higher energy than steam
D) Melting is exothermic
E) Vaporization uses kinetic heat only
11. Which of the following processes is exothermic?
A) Vaporization
B) Melting
C) Boiling
D) Condensation
E) Sublimation
12. In a heating curve, where does vaporization occur?
A) At the lowest point
B) During the steep slope
C) At the plateau after boiling starts
D) Before melting
E) Immediately after freezing
13. When 10 g of water vaporizes, how much heat is absorbed? (Use Lv = 2260 J/g)
A) 226 J
B) 4520 J
C) 2260 J
D) 22600 J
E) 11300 J
14. The boiling point of a substance is:
A) Where its temperature is highest
B) Where molecules move slowest
C) Where vapor pressure equals atmospheric pressure
D) Always 100°C
E) Where fusion happens
15. Why does condensation release energy?
A) Molecules gain mass
B) Energy is lost as radiation
C) Molecules slow and reform attractions
D) The system absorbs light
E) Kinetic energy increases
16. What is the main factor affecting the heat of vaporization?
A) Molar mass
B) Strength of intermolecular forces
C) Color of the liquid
D) Volume of gas
E) Type of container
17. Which statement is true?
A) Heat of vaporization = heat of condensation (in magnitude)
B) Vaporization cools the environment
C) Boiling is a chemical change
D) Condensation requires heat input
E) All liquids have the same Lv
18. Why does sweating cool the body?
A) Skin temperature rises
B) Water evaporates, absorbing body heat
C) Water freezes
D) Skin contracts
E) Salt absorbs moisture
19. Which of the following has the highest heat of vaporization?
A) Alcohol
B) Water
C) Acetone
D) Benzene
E) Ether
20. In Q = mLv, what does Lv stand for?
A) Latent volume
B) Level of vapor
C) Heat of vaporization
D) Latent viscosity
E) Light vapor
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Answers and Explanations
1. C – Heat of vaporization is the energy required to convert liquid to gas at its boiling point.
2. C – Heat of condensation is the energy released as gas becomes liquid.
3. D – The heat of vaporization for water is approximately 2260 J/g.
4. C – Condensation releases energy to the surroundings.
5. B – Q = mLv calculates the heat involved in vaporization or condensation.
6. B – Q = 5 g × 2260 J/g = 11,300 J
7. D – Temperature remains constant because heat breaks intermolecular forces, not raising temp.
8. B – Molecules absorb energy and move more freely in the gas state.
9. C – Condensation is an exothermic process.
10. B – Vaporization requires more energy to completely separate molecules.
11. D – Condensation is exothermic (heat is released).
12. C – Vaporization occurs at the flat part of the heating curve after boiling starts.
13. D – Q = 10 g × 2260 J/g = 22,600 J
14. C – Boiling point is when vapor pressure equals atmospheric pressure.
15. C – Molecules slow down and form attractions, releasing energy.
16. B – Intermolecular forces greatly affect heat of vaporization.
17. A – Heat of vaporization and condensation are equal in magnitude but opposite in sign.
18. B – Evaporation absorbs body heat, cooling the skin.
19. B – Water has a very high heat of vaporization due to strong hydrogen bonds.
20. C – "Lv" refers to latent heat of vaporization.
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