Which of the following correctly describes a heating-cooling curve for a pure substance?

• A. It shows a continuous rise in temperature, even during phase changes.
• B. It shows temperature changes as a substance is heated or cooled, with plateaus representing phase changes where temperature remains constant.
• C. It displays only the increase in temperature during heating, without any plateaus.
• D. It represents the pressure changes of a substance as it is heated or cooled.

Answer: (B)

Verified step by step guidance

1. Understand that a heating-cooling curve represents how the temperature of a pure substance changes as heat is added or removed.
2. Recognize that during phase changes (such as melting or boiling), the temperature remains constant even though heat is still being added or removed; this creates plateaus on the curve.
3. Note that between phase changes, the temperature of the substance changes continuously, either increasing during heating or decreasing during cooling.
4. Identify that the plateaus correspond to the energy used to overcome intermolecular forces during phase transitions, not to increase temperature.
5. Conclude that the correct description of a heating-cooling curve includes temperature changes with flat regions (plateaus) where the temperature remains constant during phase changes.