Questions on Melting
20 Multiple-Choice Questions on Melting
1. Melting is the process by which a:
A) Gas turns into a liquid
B) Liquid turns into a solid
C) Solid turns into a liquid
D) Liquid turns into a gas
E) Gas turns into a solid
2. The melting point of a substance is defined as:
A) The temperature at which it condenses
B) The temperature at which it freezes
C) The temperature at which it turns into gas
D) The temperature at which it becomes a liquid
E) The temperature at which it decomposes
3. During melting, the temperature of the substance:
A) Decreases continuously
B) Increases rapidly
C) Remains constant until all is melted
D) Doubles in value
E) Fluctuates randomly
4. Which of the following processes is endothermic?
A) Freezing
B) Condensation
C) Melting
D) Deposition
E) Sublimation (reverse)
5. What happens to the particles of a solid as it melts?
A) They move slower and closer
B) They stop moving
C) They become fixed in position
D) They move faster and further apart
E) They lose energy and bond more tightly
6. The melting point of pure ice at 1 atm pressure is:
A) 0°C
B) 32°C
C) 100°C
D) -273°C
E) 4°C
7. Which factor can affect the melting point of a substance?
A) Amount of color
B) Volume of substance
C) External pressure
D) Surface area
E) Shape of the particles
8. Substances with stronger intermolecular forces tend to have:
A) Lower melting points
B) Unpredictable melting behavior
C) Higher melting points
D) No melting point
E) The same melting point as water
9. What is a melting curve used to show?
A) The density change during freezing
B) The vapor pressure of solids
C) The temperature and pressure at which a solid melts
D) The energy released during cooling
E) The rate of boiling
10. Which of the following substances would likely have the lowest melting point?
A) Sodium chloride
B) Ice
C) Iron
D) Wax
E) Diamond
11. When a substance melts, the energy added is used to:
A) Increase its temperature
B) Strengthen its bonds
C) Increase the kinetic energy only
D) Break intermolecular forces
E) Ionize the atoms
12. What occurs at the molecular level during melting?
A) Particles lose kinetic energy
B) Molecules become more ordered
C) Molecules overcome attractive forces
D) Bonds are created
E) Electrons are transferred
13. A substance that has a sharp melting point is likely:
A) A pure substance
B) A mixture
C) A solution
D) An alloy
E) Amorphous solid
14. Amorphous solids:
A) Have a definite melting point
B) Have no melting point
C) Soften over a range of temperatures
D) Freeze at 100°C
E) Are liquids at room temperature
15. Why does the melting point of salt differ from that of sugar?
A) They have the same structure
B) They have different pH levels
C) They have different molecular structures and bonding
D) Sugar is a gas
E) Salt has more water
16. What kind of bond leads to the highest melting points?
A) Hydrogen bonds
B) Ionic bonds
C) Metallic bonds
D) Covalent bonds
E) Van der Waals forces
17. What is the term for the opposite process of melting?
A) Vaporization
B) Freezing
C) Condensation
D) Boiling
E) Sublimation
18. In a phase change diagram, the flat line at the melting point indicates:
A) No change in energy
B) Constant temperature, energy used for phase change
C) Increase in temperature
D) Volume increase
E) Increase in molecular speed
19. Which of the following will lower the melting point of ice?
A) Decreasing pressure
B) Adding salt
C) Heating it quickly
D) Using a cold surface
E) Increasing pH
20. The melting point of a substance can help identify:
A) Its color
B) Its boiling point
C) Its molar mass
D) Its identity and purity
E) Its atomic number
Answer Key with Explanations
1. C – Melting is the transition from solid to liquid.
2. D – The melting point is the temperature at which a solid becomes a liquid.
3. C – The temperature remains constant during the phase change until all is melted.
4. C – Melting is endothermic because it absorbs heat.
5. D – As solids melt, particles move faster and spread out.
6. A – Ice melts at 0°C under normal pressure (1 atm).
7. C – Pressure affects the melting point, especially in substances like ice.
8. C – Stronger forces = more energy needed to melt = higher melting point.
9. C – A melting curve shows the phase change with respect to pressure and temperature.
10. D – Wax is molecular and has weak forces = low melting point.
11. D – Energy during melting breaks intermolecular forces, not bonds.
12. C – Molecules overcome attractions holding them in a solid state.
13. A – Pure substances have sharp melting points; mixtures do not.
14. C – Amorphous solids soften over a range, not a precise point.
15. C – Salt (ionic) and sugar (covalent) differ in structure and bonding.
16. B – Ionic bonds are strong and lead to high melting points.
17. B – Freezing is the reverse of melting.
18. B – Energy is used to change the phase, not to raise temperature.
19. B – Adding solute like salt lowers the freezing/melting point (freezing point depression).
20. D – Melting point helps confirm a substance’s identity and purity.
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