Closed System Definition (Science)

What Is a Closed System in Thermodynamics?

A closed system doesn't allow certain types of transfer. For example, a closed jar doesn't allow mass transfer.
A closed system doesn't allow certain types of transfer. For example, a closed jar doesn't allow mass transfer. Image by Catherine MacBride / Getty Images
by Anne Marie Helmenstine, Ph.D.
Updated December 09, 2017

A closed system is a concept used in thermodynamics (physics and engineering) and in chemistry.

Closed System Definition

A closed system is a type of thermodynamic system where mass is conserved within the boundaries of the system, but energy is allowed to freely enter or exit the system.

In chemistry, a closed system is one in which neither reactants nor products can enter or escape, yet which allows energy transfer (heat and light). A closed system may be used for experiments where temperature isn't a factor.