What distinguishes an open system from a closed system in thermodynamics?

In thermodynamics, an open system is characterized by the ability to exchange both energy and matter with its surroundings. This means that in an open system, not only can heat energy be transferred in or out, but mass can also flow into or out of the system. This is crucial for various applications, such as in engines, biological systems, and many other processes where interactions with the environment are essential for operation.

For example, consider a boiling pot of water on the stove. Steam (matter) escapes into the environment while heat (energy) is transferred from the stove to the pot, showcasing the properties of an open system.

In contrast, closed systems restrict the exchange of matter with their surroundings but can still exchange energy. Therefore, while energy can flow in or out of a closed system, the total mass within the system remains constant. Understanding this distinction is fundamental in thermodynamics, as it influences how different systems behave under various conditions.