When do two objects reach thermal equilibrium?

Two objects reach thermal equilibrium when they are at the same temperature; this is the condition under which there is no net heat transfer between them. When the temperatures of the two objects become equal, energy transfer in the form of heat ceases.

In thermal equilibrium, the objects' temperatures stabilize, meaning they are both experiencing the same average kinetic energy of their particles. This is a fundamental concept in thermodynamics, emphasizing that heat naturally flows from a hotter object to a cooler one until both objects reach the same temperature. Only at this point does the transfer of heat stop, fulfilling the condition for thermal equilibrium.

Thus, the state of being at a constant temperature applies to the scenario of thermal equilibrium, as it directly indicates that no heat transfer is occurring between the objects.