Questions on Heating and Cooling Curves
20 Multiple-Choice Questions: Heating and Cooling Curves
Questions:
1. What does a flat line on a heating curve represent?
A) A change in pressure
B) Constant temperature but increasing mass
C) A phase change
D) Increasing kinetic energy
E) Decreasing temperature
2. During a phase change, what remains constant?
A) Heat
B) Temperature
C) Volume
D) Pressure
E) Energy
3. Which of the following occurs during the sloped portions of a heating curve?
A) Temperature stays constant
B) A phase change occurs
C) Only potential energy increases
D) Only kinetic energy increases
E) Mass increases
4. What is happening to the energy during the flat regions of the curve?
A) Energy is being lost
B) Energy is decreasing
C) Energy is used to increase temperature
D) Energy is used to break or form bonds
E) No energy is used
5. The boiling point of a substance on a heating curve is identified by:
A) The first plateau
B) The highest peak
C) The sloping region
D) The second plateau
E) The lowest point
6. In a cooling curve, what happens during a plateau?
A) Kinetic energy increases
B) Kinetic energy decreases
C) The substance is changing phase
D) Temperature is rising
E) The substance is evaporating
7. Which type of energy increases during the sloped segments?
A) Electrical
B) Thermal
C) Potential
D) Kinetic
E) Nuclear
8. What is the heat of fusion?
A) Energy to vaporize a solid
B) Energy to condense a liquid
C) Energy to melt a solid
D) Energy to raise temperature
E) Energy to freeze a gas
9. What is the heat of vaporization?
A) Energy required to freeze a liquid
B) Energy to condense a gas
C) Energy to vaporize a liquid
D) Energy to melt a solid
E) Energy to lower temperature
10. At what phase change does heat of fusion apply?
A) Boiling
B) Melting
C) Condensation
D) Sublimation
E) Deposition
11. Why does temperature not change during a phase change?
A) The system is insulated
B) Energy is used to change the substance’s color
C) All energy goes into changing the state
D) There is no energy input
E) The atoms stop moving
12. What happens to potential energy during a phase change?
A) It stays constant
B) It decreases
C) It increases
D) It becomes zero
E) It becomes kinetic
13. In a heating curve for water, the segment between 0°C and 100°C represents:
A) Melting
B) Freezing
C) Liquid water heating
D) Boiling
E) Sublimation
14. On a cooling curve, which occurs first as heat is removed?
A) Freezing
B) Condensation
C) Decrease in temperature
D) Increase in kinetic energy
E) Vaporization
15. What would make the slope of a heating curve less steep?
A) Lower mass
B) Higher specific heat
C) Higher pressure
D) Less energy input
E) Melting instead of boiling
16. Which substance will have a flatter slope on the heating curve?
A) One with lower specific heat
B) One with higher specific heat
C) One with high thermal conductivity
D) One with low boiling point
E) One that sublimates
17. When steam condenses into water, which energy is released?
A) Heat of fusion
B) Heat of melting
C) Heat of vaporization
D) Latent energy
E) Kinetic energy
18. A cooling curve ends at which state of matter?
A) Gas
B) Plasma
C) Liquid
D) Solid
E) Mixture
19. Which graph correctly shows the relationship between time and temperature during constant heating of a pure substance?
A) A straight line
B) An exponential curve
C) A staircase with flat and sloped sections
D) A downward parabola
E) A sine wave
20. What do the plateaus in heating/cooling curves depend on?
A) Pressure only
B) Mass of substance
C) Nature of the substance and heat of phase change
D) Volume only
E) Shape of the container
Extended Answers and Explanations:
1. C) A phase change
→ Flat lines indicate a change in state (e.g., melting, boiling) with constant temperature.
2. B) Temperature
→ During a phase change, temperature stays constant while energy is used for bond breaking/forming.
3. D) Only kinetic energy increases
→ In sloped sections, temperature rises, so kinetic energy increases.
4. D) Energy is used to break or form bonds
→ The energy goes into changing the state, not increasing temperature.
5. D) The second plateau
→ The second flat region corresponds to boiling (liquid to gas transition).
6. C) The substance is changing phase
→ Like heating, flat regions in cooling represent phase changes like freezing or condensation.
7. D) Kinetic
→ In the sloped segments, temperature increases, meaning kinetic energy increases.
8. C) Energy to melt a solid
→ Heat of fusion is the energy required to melt 1 mole (or gram) of a solid.
9. C) Energy to vaporize a liquid
→ Heat of vaporization is the energy needed to convert a liquid to gas.
10. B) Melting
→ Melting involves the heat of fusion.
11. C) All energy goes into changing the state
→ Energy is used to overcome intermolecular forces rather than increase temperature.
12. C) It increases
→ During melting or boiling, potential energy increases as particles move apart.
13. C) Liquid water heating
→ The temperature increase between melting and boiling is the heating of liquid water.
14. C) Decrease in temperature
→ Temperature begins to fall before any phase change occurs in a cooling curve.
15. B) Higher specific heat
→ Higher specific heat means more energy is required to raise temperature, so slope is flatter.
16. B) One with higher specific heat
→ It takes longer (more energy) to raise the temperature, producing a flatter slope.
17. C) Heat of vaporization
→ When gas condenses, it releases the same energy absorbed during vaporization.
18. D) Solid
→ The final phase after cooling a liquid completely is the solid state.
19. C) A staircase with flat and sloped sections
→ Heating curves alternate between increasing temperature and flat phase changes.
20. C) Nature of the substance and heat of phase change
→ Each substance has unique melting/boiling points and phase change enthalpies.
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