1. The temperature at which a solid changes into a liquid is called its:
A.
Melting point
B.
Boiling point
C.
Freezing point of a gas
D.
Condensation point
Correct Answer:
Melting point
Explanation:
The melting point is the temperature at which a solid changes into a liquid.
2. At the melting point of a pure solid, the solid and liquid phases can exist:
A.
Together in equilibrium
B.
Only as gases
C.
Only at absolute zero
D.
Without any temperature
Correct Answer:
Together in equilibrium
Explanation:
At the melting point, solid and liquid phases coexist in equilibrium.
3. What happens to the temperature of a pure solid while it is melting at constant pressure?
A.
It remains constant
B.
It continuously increases
C.
It continuously decreases
D.
It becomes zero
Correct Answer:
It remains constant
Explanation:
During melting, heat is used for the phase change, so the temperature remains constant until the solid has melted.
4. Which phase change occurs at the melting point?
A.
Solid to liquid
B.
Liquid to gas
C.
Gas to liquid
D.
Liquid to solid only
Correct Answer:
Solid to liquid
Explanation:
The melting point is specifically associated with the change from solid to liquid.
5. The melting point of ice at normal atmospheric pressure is approximately:
A.
0 °C
B.
50 °C
C.
100 °C
D.
273 °C
Correct Answer:
0 °C
Explanation:
At normal atmospheric pressure, ice melts at approximately 0 °C.
6. For a pure crystalline substance, the melting point is generally:
A.
A fixed temperature
B.
A continuously changing temperature
C.
Always above 100 °C
D.
Independent of the substance
Correct Answer:
A fixed temperature
Explanation:
A pure crystalline substance melts at a definite temperature under a specified pressure.
7. When a solid reaches its melting point, the added heat mainly helps to:
A.
Change the solid into a liquid
B.
Lower the melting point to zero
C.
Convert the solid directly into a gas
D.
Remove all particles from the substance
Correct Answer:
Change the solid into a liquid
Explanation:
At the melting point, added heat provides energy for the solid-to-liquid phase change.
8. The melting point is measured under a particular pressure because phase-change temperature can depend on:
A.
Pressure
B.
The color of the container
C.
The shape of the thermometer
D.
The name of the laboratory
Correct Answer:
Pressure
Explanation:
The temperature of a phase change, including melting, can vary with pressure.
9. Which statement correctly describes a substance at its melting point?
A.
It may contain both solid and liquid phases
B.
It must contain only gas
C.
It cannot absorb heat
D.
Its particles stop moving completely
Correct Answer:
It may contain both solid and liquid phases
Explanation:
At the melting point, solid and liquid phases can be present at the same time.
10. If a solid is heated below its melting point, the supplied heat generally causes its:
A.
Temperature to increase
B.
Temperature to remain constant during melting
C.
Immediate change into a gas
D.
Melting point to disappear
Correct Answer:
Temperature to increase
Explanation:
Before the melting point is reached, added heat usually increases the temperature of the solid.
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