chemistry : class11 Latent Heat of Fusion : Melting point : States of Matter: Gases and Liquids MCQ Questions and Answers
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Latent Heat of Fusion
MCQ questions and answers.
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MCQ Questions
1. What is meant by the latent heat of fusion of a substance?
A.
The heat required to change a liquid into a gas at constant temperature
B.
The heat required to change a solid into a liquid at its melting point without changing temperature
C.
The heat required to increase the temperature of a solid by 1°C
D.
The heat released when a gas changes into a liquid
Correct Answer:
The heat required to change a solid into a liquid at its melting point without changing temperature
Explanation:
Latent heat of fusion is the heat needed to convert unit mass of a solid into liquid at its melting point without a change in temperature.
2. During the melting of a pure solid at its melting point, its temperature generally:
A.
Increases continuously
B.
Decreases continuously
C.
Remains constant
D.
Becomes zero
Correct Answer:
Remains constant
Explanation:
The heat supplied during melting is used to overcome intermolecular forces and change the state, so the temperature remains constant.
3. What is the SI unit of specific latent heat of fusion?
A.
J kg⁻¹
B.
J kg⁻¹ K⁻¹
C.
N m⁻¹
D.
kg J⁻¹
Correct Answer:
J kg⁻¹
Explanation:
Specific latent heat of fusion is heat required per unit mass, so its SI unit is joule per kilogram, written as J kg⁻¹.
4. Which formula is used to calculate the heat required to melt a mass of a solid?
A.
Q = mcΔT
B.
Q = mL_f
C.
Q = mgh
D.
Q = VIt
Correct Answer:
Q = mL_f
Explanation:
The heat required for fusion is given by Q = mL_f, where m is the mass and L_f is the specific latent heat of fusion.
5. How much heat is required to melt 2 kg of a substance having a specific latent heat of fusion of 100 J kg⁻¹?
A.
50 J
B.
100 J
C.
200 J
D.
500 J
Correct Answer:
200 J
Explanation:
Using Q = mL_f, Q = 2 kg × 100 J kg⁻¹ = 200 J.
6. If the mass of a substance is doubled while its specific latent heat of fusion remains unchanged, the heat required for melting becomes:
A.
Half
B.
Double
C.
Unchanged
D.
Zero
Correct Answer:
Double
Explanation:
From Q = mL_f, the heat required is directly proportional to mass when the specific latent heat of fusion is constant.
7. The latent heat absorbed by a solid during fusion is mainly used to:
A.
Increase its temperature
B.
Break or weaken intermolecular forces
C.
Decrease its mass
D.
Increase its density immediately
Correct Answer:
Break or weaken intermolecular forces
Explanation:
During fusion, the supplied heat changes the arrangement of particles by overcoming intermolecular attractions rather than raising the temperature.
8. A substance requires 600 J of heat to melt 3 kg of it. What is its specific latent heat of fusion?
A.
100 J kg⁻¹
B.
200 J kg⁻¹
C.
300 J kg⁻¹
D.
1800 J kg⁻¹
Correct Answer:
200 J kg⁻¹
Explanation:
Using L_f = Q/m, L_f = 600 J ÷ 3 kg = 200 J kg⁻¹.
9. When a liquid freezes at its freezing point, it:
A.
Absorbs latent heat of fusion
B.
Releases latent heat of fusion
C.
Absorbs no heat and changes temperature rapidly
D.
Changes directly into a gas
Correct Answer:
Releases latent heat of fusion
Explanation:
Freezing is the reverse of fusion. The liquid releases the same type of latent heat as its particles form a solid structure.
10. Two substances have the same mass. Which substance requires more heat to melt completely?
A.
The substance with the smaller specific latent heat of fusion
B.
The substance with the larger specific latent heat of fusion
C.
Both always require zero heat
D.
The substance with the lower melting temperature only
Correct Answer:
The substance with the larger specific latent heat of fusion
Explanation:
For equal masses, Q = mL_f shows that the substance with the larger specific latent heat of fusion requires more heat to melt.
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