Thermodynamic systems – definition of a closed system A closed system is one in which heat and work may cross the boundary, but the mass of the working substance does not cross the system boundary. Is this statement correct?

Introduction / Context:
Identifying the correct type of thermodynamic system is essential for applying conservation laws. Systems are classified as closed, open, or isolated based on mass and energy exchange across the boundary.

Given Data / Assumptions:

• System boundary is well defined.
• Energy can be transferred as heat and/or work.
• No mass transfer occurs across the boundary.

Concept / Approach:
A closed system (control mass) keeps its mass fixed, but energy exchange is allowed. An open system (control volume) allows mass, heat, and work to cross. An isolated system allows neither mass nor energy to cross.

Step-by-Step Solution:
State the definition of a closed system: mass is constant, heat and work may cross.Check boundary conditions: whether rigid or deformable, the classification depends on mass transfer, not on mechanical flexibility.Therefore the statement given is correct.

Verification / Alternative check:
Examples include a sealed piston–cylinder with moving piston (work crosses) and heated walls (heat crosses) but no mass leaves or enters.

Why Other Options Are Wrong:

• “No”: contradicts the standard definition.
• Restrictions to ideal gases or rigid boundaries are unnecessary for the definition.
• “Heat cannot cross a closed boundary” describes an isolated system, not a closed one.

Common Pitfalls:
Confusing closed with isolated; the latter forbids energy transfer as well.

Final Answer:
Yes