chemistry : class11 Heating Curve : Melting point : States of Matter: Gases and Liquids MCQ Questions and Answers
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Heating Curve
MCQ questions and answers.
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MCQ Questions
1. What is represented on the horizontal axis of a typical heating curve?
A.
Temperature of the substance
B.
Heat added to the substance
C.
Mass of the substance
D.
Volume of the container
Correct Answer:
Heat added to the substance
Explanation:
A heating curve shows how the temperature changes as heat is added, so the horizontal axis commonly represents heat supplied.
2. What does a horizontal portion of a heating curve indicate during melting?
A.
The substance is cooling rapidly
B.
The temperature remains constant while melting occurs
C.
The substance has completely vaporized
D.
No heat is being supplied
Correct Answer:
The temperature remains constant while melting occurs
Explanation:
During melting, added heat is used to overcome forces between particles, so the temperature remains constant until melting is complete.
3. At which part of a heating curve does a solid change into a liquid?
A.
The melting plateau
B.
The initial sloping section
C.
The final sloping section
D.
The cooling section
Correct Answer:
The melting plateau
Explanation:
The melting plateau is the constant-temperature region where the solid changes into a liquid.
4. What is the temperature at the melting plateau called?
A.
Boiling point
B.
Freezing point only
C.
Melting point
D.
Room temperature
Correct Answer:
Melting point
Explanation:
The constant temperature at which a solid changes into a liquid on a heating curve is called its melting point.
5. During the melting plateau of a pure substance, which phases are present together?
A.
Liquid and gas
B.
Solid and liquid
C.
Solid and gas
D.
Only gas
Correct Answer:
Solid and liquid
Explanation:
Melting is the change from solid to liquid, so both solid and liquid are present during the melting plateau.
6. What happens to the temperature of a pure substance while it is melting on a heating curve?
A.
It increases steadily
B.
It decreases steadily
C.
It remains constant
D.
It becomes zero
Correct Answer:
It remains constant
Explanation:
The temperature remains constant during melting because the supplied heat is used for the phase change rather than increasing particle motion.
7. What happens after all the solid has melted and heating continues?
A.
The liquid temperature increases
B.
The temperature remains at the melting point forever
C.
The substance immediately becomes a solid
D.
The heat supply stops automatically
Correct Answer:
The liquid temperature increases
Explanation:
Once melting is complete, further heat raises the temperature of the liquid, producing an upward-sloping section on the heating curve.
8. Which section of a heating curve usually shows the temperature increasing in a solid?
A.
The first sloping section
B.
The melting plateau
C.
The boiling plateau
D.
The final horizontal section
Correct Answer:
The first sloping section
Explanation:
Before melting begins, added heat increases the temperature of the solid, giving the first upward-sloping section.
9. Why does the melting section appear flat on a heating curve?
A.
The substance is not receiving heat
B.
The supplied heat is used for the phase change
C.
The thermometer has stopped working
D.
The mass of the substance is increasing
Correct Answer:
The supplied heat is used for the phase change
Explanation:
During melting, heat is used to overcome attractions between particles, so the temperature does not rise.
10. A substance begins melting at 80°C and remains at 80°C until melting is complete. What is its melting point?
A.
0°C
B.
40°C
C.
80°C
D.
160°C
Correct Answer:
80°C
Explanation:
The temperature of the melting plateau is the melting point, so the substance has a melting point of 80°C.
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Heating Curve
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