What characterizes a system in thermal equilibrium?

A system in thermal equilibrium is characterized by having a consistent set of macroscopic quantities that define its state. This means that properties such as temperature, pressure, and volume are uniform throughout the system and do not change over time, indicating that no net heat flow occurs within or between the systems.

In this context, macroscopic quantities are the large-scale properties that can be measured and observed, and they allow scientists to describe the state of a system effectively. When a system is in thermal equilibrium, it reflects a stable condition where these quantities are defined and remain constant.

This notion is crucial because it helps understand how energy transfer ceases between systems in proximity, leading to a balance that can be used in thermodynamics and other physical science disciplines.