Which of the following best describes what occurs at thermal equilibrium?

• A. Only one object reaches a higher temperature than the other.
• B. No net heat flow occurs between objects in contact.
• C. Objects in contact continue to exchange heat indefinitely.
• D. The temperature of each object becomes zero.

Answer: (B)

Verified step by step guidance

1. Understand the concept of thermal equilibrium: it occurs when two objects in contact no longer exchange net heat energy because they have reached the same temperature.
2. Recall the zeroth law of thermodynamics, which states that if two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other, implying equal temperatures.
3. Recognize that at thermal equilibrium, although microscopic heat exchanges may still happen, the amount of heat lost by one object equals the amount gained by the other, resulting in no net heat flow.
4. Eliminate incorrect options: one object cannot have a higher temperature than the other at equilibrium; temperatures do not become zero unless specifically cooled to absolute zero; and heat exchange does not continue indefinitely with a net flow.
5. Conclude that the best description of thermal equilibrium is that no net heat flow occurs between objects in contact because their temperatures are equal.