Question

what is the definition of thermal equilibrium?
when one object becomes significantly hotter than another.
when heat stops flowing because all kinetic energy is gone.
when two systems reach the same temperature and there is no net flow of heat between them.
when heat is actively flowing from a hot object to a cold one,

Explanation:

To determine the correct definition of thermal equilibrium, we analyze each option:

• The first option is incorrect because thermal equilibrium involves no significant temperature difference.
• The second option is wrong as kinetic energy is never "gone" (particles always have kinetic energy), and heat stops flowing when temperatures are equal, not due to lack of kinetic energy.
• The third option matches the definition: thermal equilibrium occurs when two systems have the same temperature, so no net heat flow between them.
• The fourth option describes heat transfer (like conduction), not equilibrium (where heat flow stops).

Answer:

The option: "When two systems reach the same temperature and there is no net flow of heat between them." (the third option in the list)