A Closed System Is One In Which

A Closed System is one in which only Energy crosses the system.  

System – A system is defined as a quantity of matter or a region in space chosen for study.

Surroundings – Everything external to the system is called the surroundings or the environment. 

Boundary – A real or imaginary surface that separates the system from its surroundings is called the boundary. 

 Depending upon the mass and energy interaction, the system is classified into three types.

(i) Open system 

(ii) Closed system

 (iii) Isolated system 

(i) Open System – A system is said to be open when both Mass and Energy cross the boundary.

 Example – Most engineering devices are generally open systems, air compressors, boilers, pumps, IC engines with valves etc.

 (ii) closed system – A system is said to be closed if its Mass remains fixed or constant, but there may be energy transfer into or out of the system. There is no mass entering into or exiting out of the system boundary. 

Example – a certain quantity of fluid in a completely enclosed cylinder, Tea in the kettle, an automobile engine without a valve etc

(iii) Isolated system – A system is said to be isolated when there is no interaction between the system and the surroundings. It is of fixed Mass and Energy, and there is no mass or energy transfer across the system boundary.

 Example – thermo-flask, Universe (since all energy interaction taking place between system and surrounding which is the part of the Universe)

 Summary

A Closed System is one in which

(i) Only energy(Heat & Work) interaction happens in a closed system, and no mass interaction. 

(ii) The identity of mass is fixed. 

(iii) If a system is defined as a certain quantity of matter, it is always a closed system since the system contains the same matter, and there can be no transfer of mass across its boundary.

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