Which description defines a closed system?

Which description defines a closed system?

• A. No Mass Transfer Across Boundaries, Energy Exchange Possible
• B. Mass Transfer Across Boundaries, With Energy Exchange
• C. No Mass Or Energy Transfer Across Boundaries
• D. Energy Transfer Only, No Mass Exchange

Answer: (A)

In a closed system, mass stays inside the boundaries while energy can cross them. That means no material can enter or leave, but heat or work can flow across the boundary. The statement that exactly matches this is: no mass transfer across the boundaries, energy exchange possible. An example is a gas in a sealed piston that can be heated or cooled (energy crosses as heat) and can do work on its surroundings, yet none of the gas leaves the container. If mass could cross the boundary, it would be an open system. If neither mass nor energy crosses, it’s an isolated system. So the defining feature is preserving mass inside while allowing energy exchange with the surroundings.

In a closed system, mass stays inside the boundaries while energy can cross them. That means no material can enter or leave, but heat or work can flow across the boundary. The statement that exactly matches this is: no mass transfer across the boundaries, energy exchange possible. An example is a gas in a sealed piston that can be heated or cooled (energy crosses as heat) and can do work on its surroundings, yet none of the gas leaves the container.

If mass could cross the boundary, it would be an open system. If neither mass nor energy crosses, it’s an isolated system. So the defining feature is preserving mass inside while allowing energy exchange with the surroundings.