Change of state and latent heat - Question Bank

1. Which of the following phase changes requires the most energy per kilogram for water?
A) Melting 1 kg of ice at 0°C to water at 0°C
B) Boiling 1 kg of water at 100°C to steam at 100°C
C) Heating 1 kg of water from 0°C to 100°C
D) Cooling 1 kg of water from 100°C to 0°C
2. What is the value of the latent heat of fusion of water in SI units?
A) 3.34 x 10^5 J/kg
B) 2.26 x 10^6 J/kg
C) 4.18 x 10^3 J/kg°C
D) 334 J/kg
3. Dry ice (solid CO2) sublimes at atmospheric pressure. This process requires:
A) Heat absorption from the surroundings
B) Heat release to the surroundings
C) No heat exchange
D) A decrease in temperature
4. The heat absorbed or released during a change of state is called:
A) Specific heat
B) Heat capacity
C) Latent heat
D) Mechanical equivalent of heat
5. If the pressure on the surface of water is increased, its boiling point will:
A) Decrease
B) Increase
C) Remain the same
D) Become undefined
6. Which of the following phase transitions is exothermic (releases heat)?
A) Melting
B) Vaporization
C) Sublimation
D) Condensation
7. Consider the process of boiling water. During boiling, the energy supplied is primarily used to:
A) Increase the kinetic energy of water molecules.
B) Increase the potential energy of water molecules by separating them.
C) Increase the vibrational energy of water molecules.
D) Increase the surface tension of water.
8. The latent heat of vaporization of a substance is the energy required to change:
A) 1 kg of solid to 1 kg of liquid at melting point
B) 1 kg of liquid to 1 kg of gas at boiling point
C) 1 kg of solid to 1 kg of gas at sublimation point
D) 1 kg of gas to 1 kg of liquid at condensation point
9. A substance is heated at a constant rate. Its temperature-time graph shows a plateau during melting and boiling. The slope of the plateau represents:
A) Specific heat capacity
B) Latent heat of fusion or vaporization
C) Rate of heating
D) Specific gravity
10. If the specific latent heat of fusion of ice is 3.34 x 10^5 J/kg, how much heat is needed to convert 20 g of ice at -10°C to water at 0°C? (Specific heat of ice = 2100 J/kg°C)
A) 6680 J
B) 7348 J
C) 66800 J
D) 73480 J
11. The phenomenon of Regelation is observed when:
A) Ice melts faster under pressure.
B) Water freezes.
C) Steam condenses.
D) A solid sublimes.
12. Which phase transition involves the greatest change in intermolecular potential energy per unit mass?
A) Melting
B) Freezing
C) Vaporization
D) Condensation
13. When water boils, the molecules gain energy to:
A) Move closer together.
B) Break free from intermolecular forces.
C) Vibrate more intensely in fixed positions.
D) Form a more ordered structure.
14. The heat required to raise the temperature of 1 kg of a substance by 1°C is called its:
A) Specific latent heat
B) Specific heat capacity
C) Latent heat
D) Heat capacity
15. If 10 g of a solid melts completely at its melting point by absorbing 840 J of heat, what is the specific latent heat of fusion?
A) 84 J/g
B) 8.4 J/g
C) 8400 J/g
D) 0.84 J/g
16. Which of the following best describes the energy change during sublimation?
A) Energy is released.
B) Energy is absorbed.
C) No energy change occurs.
D) Energy change depends on pressure.
17. The triple point of a substance is the temperature and pressure at which:
A) Solid and liquid coexist
B) Liquid and gas coexist
C) Solid and gas coexist
D) Solid, liquid, and gas coexist in equilibrium
18. A pressure cooker cooks food faster because:
A) The temperature inside is lower than atmospheric pressure.
B) The pressure inside is higher, raising the boiling point of water.
C) The pressure inside is lower, lowering the boiling point of water.
D) The heat transfer is more efficient due to convection.
19. The boiling point of a liquid is affected by:
A) The surface area of the liquid
B) The volume of the liquid
C) The external pressure
D) The color of the liquid
20. Which of the following statements about phase transitions is correct?
A) During boiling, heat is released.
B) During condensation, temperature increases.
C) During melting, heat is absorbed.
D) During sublimation, temperature decreases.
21. During the melting of ice at 0°C, the heat absorbed is used to:
A) Increase the kinetic energy of water molecules.
B) Increase the potential energy of water molecules by breaking the bonds.
C) Decrease the kinetic energy of water molecules.
D) Decrease the potential energy of water molecules.
22. What is the unit of specific latent heat?
A) J/kg
B) J/kg°C
C) J/°C
D) J
23. If the latent heat of fusion of a substance is Lf and its latent heat of vaporization is Lv, then usually:
A) Lv < Lf
B) Lv > Lf
C) Lv = Lf
D) Lv = 0
24. The specific latent heat of vaporization is generally higher than the specific latent heat of fusion for most substances because:
A) More energy is needed to overcome intermolecular forces in the liquid state to form a gas.
B) Less energy is needed to overcome intermolecular forces in the liquid state to form a gas.
C) The temperature change is greater during vaporization.
D) The pressure change is greater during vaporization.
25. Which of the following is an example of sublimation?
A) Water turning into ice
B) Iodine crystals turning into vapor
C) Steam turning into water droplets
D) Alcohol evaporating from the skin
26. The change of state from gas to solid without passing through the liquid state is called:
A) Sublimation
B) Condensation
C) Deposition
D) Evaporation
27. When a liquid evaporates, it causes cooling because:
A) Heat is absorbed from the surroundings.
B) Heat is released to the surroundings.
C) The liquid molecules lose kinetic energy.
D) The liquid molecules gain potential energy.
28. Evaporation is a surface phenomenon. Which factor does NOT affect the rate of evaporation?
A) Surface area
B) Temperature
C) Humidity
D) Pressure of the gas above the liquid
29. The process where a liquid turns into a gas below its boiling point is called:
A) Boiling
B) Evaporation
C) Condensation
D) Sublimation
30. What happens to the internal energy of a substance when it melts at constant temperature?
A) It decreases.
B) It remains the same.
C) It increases.
D) It first decreases then increases.
31. The amount of heat required to change 1 kg of a solid into liquid at its melting point is given by:
A) Q = mcΔT
B) Q = mL
C) Q = V/R
D) Q = P/t
32. Which of the following statements is FALSE regarding a change of state?
A) Energy is exchanged with the surroundings.
B) The temperature remains constant during the phase transition.
C) The molecular arrangement and potential energy change.
D) The kinetic energy of molecules changes significantly.
33. A substance changes from solid to liquid at a fixed temperature called its:
A) Boiling point
B) Melting point
C) Sublimation point
D) Critical point
34. The specific latent heat of fusion of ice is approximately:
A) 3.34 x 10^5 J/kg
B) 2.26 x 10^6 J/kg
C) 4.18 J/g°C
D) 334 J/g
35. Which of the following processes involves the release of latent heat?
A) Boiling of water
B) Melting of wax
C) Sublimation of naphthalene
D) Condensation of water vapor
36. Which of the following processes involves the absorption of latent heat?
A) Condensation of steam
B) Freezing of water
C) Melting of ice
D) Sublimation of dry ice (solid CO2)
37. If 2 kg of water at 100°C is converted into steam at 100°C, how much heat energy is absorbed? (Latent heat of vaporization of water = 2.26 x 10^6 J/kg)
A) 2.26 x 10^6 J
B) 4.52 x 10^6 J
C) 1.13 x 10^6 J
D) 4.52 x 10^7 J
38. The energy required to convert 1 gram of a liquid into vapor at its boiling point without any change in temperature is known as:
A) Specific heat capacity
B) Specific latent heat of fusion
C) Specific latent heat of vaporization
D) Specific latent heat of sublimation
39. The process of changing from gas to liquid is called:
A) Vaporization
B) Evaporation
C) Condensation
D) Sublimation
40. The boiling point of water at standard atmospheric pressure is:
A) 0 degrees Celsius
B) 100 degrees Celsius
C) 373.15 Kelvin
D) 212 degrees Fahrenheit
41. When steam at 100°C condenses into water at 100°C, heat is:
A) Absorbed
B) Released
C) Neither absorbed nor released
D) Absorbed and then released
42. Which of the following has the highest specific latent heat of fusion?
A) Water
B) Ice
C) Aluminum
D) Lead
43. If 5 kg of ice at 0°C is melted into water at 0°C, how much heat energy is absorbed? (Latent heat of fusion of ice = 3.34 x 10^5 J/kg)
A) 1.67 x 10^6 J
B) 3.34 x 10^5 J
C) 1.67 x 10^5 J
D) 3.34 x 10^6 J
44. The latent heat of vaporization for water at its boiling point is approximately:
A) 3.34 x 10^5 J/kg
B) 2.26 x 10^6 J/kg
C) 80 J/kg
D) 4200 J/kg
45. Which type of latent heat is involved when ice melts into water?
A) Latent heat of vaporization
B) Latent heat of sublimation
C) Latent heat of fusion
D) Latent heat of condensation
46. The latent heat of fusion for a substance is the heat required to change:
A) 1 kg of solid to 1 kg of liquid at its melting point
B) 1 kg of liquid to 1 kg of gas at its boiling point
C) 1 kg of solid to 1 kg of gas at its sublimation point
D) 1 kg of gas to 1 kg of liquid at its condensation point
47. Latent heat is defined as the heat energy absorbed or released during a change of state at:
A) Constant pressure and increasing temperature
B) Constant temperature and increasing pressure
C) Constant temperature and constant pressure
D) Increasing temperature and increasing pressure
48. During a change of state, such as melting or boiling, the temperature of the substance:
A) Increases continuously
B) Decreases continuously
C) Remains constant
D) Fluctuates rapidly
49. What is the melting point of ice at standard atmospheric pressure?
A) 0 degrees Celsius
B) 100 degrees Celsius
C) -18 degrees Celsius
D) 32 degrees Fahrenheit
50. The process of changing from solid to gas without passing through the liquid state is called:
A) Fusion
B) Vaporization
C) Sublimation
D) Deposition
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