Closed system

Definition

A closed system is a thermodynamic system in which matter cannot enter or leave, but energy can be exchanged with its surroundings. It is an idealized concept used to simplify the analysis of energy transfer processes.

5 Must Know Facts For Your Next Test

1. In a closed system, mass remains constant over time because no mass crosses the system boundary.
2. Energy transfer in a closed system can occur through heat and work interactions.
3. The First Law of Thermodynamics applies to closed systems and states that the change in internal energy equals the heat added to the system minus the work done by the system.
4. Closed systems are often used in thermodynamic analysis to model real-world processes like piston-cylinder assemblies, where gases are compressed or expanded without mass exchange.
5. Entropy changes in a closed system depend on reversible and irreversible processes; however, for any cyclic process, the net entropy change over one complete cycle is zero.

Review Questions

• What distinguishes a closed system from an open or isolated system?
• How does the First Law of Thermodynamics apply to a closed system?
• Can entropy change in a closed system during non-reversible processes?

Related terms

Open System: A thermodynamic system where both matter and energy can cross the boundaries.

Isolated System: A thermodynamic system that does not exchange either matter or energy with its surroundings.

Internal Energy: The total energy contained within a thermodynamic system, including kinetic and potential energy at the microscopic level.