Q.13 Which one of the following statements is correct in the context of thermodynamics?
(A) In a closed system, neither mass nor energy is transferred across the system
boundary
(B) In a closed system, both mass and energy can be transferred across the system
boundary
(C) The total energy of the system is the sum of kinetic and potential energies
(D) In a closed system, only energy can be transferred across the system boundary and
not mass

Understanding Closed Systems in Thermodynamics: Correct Answer Revealed

Closed systems in thermodynamics allow energy transfer but not mass, making option (D) the correct choice for this key concept often tested in exams.

Correct Answer

Option (D) states: “In a closed system, only energy can be transferred across the system boundary and not mass.”​

This definition aligns with standard thermodynamics principles, where a closed system has fixed mass but permits heat and work exchanges.​

Option Analysis

Incorrect Options

• (A) In a closed system, neither mass nor energy is transferred across the system boundary.
  This describes an isolated system, not a closed one, as closed systems allow energy flow.​

• (B) In a closed system, both mass and energy can be transferred across the system boundary.
  This defines an open system, where mass enters or exits, such as in turbines or compressors.​

• (C) The total energy of the system is the sum of kinetic and potential energies.
  Total energy includes internal, kinetic, and potential energies; omitting internal energy (microscopic forms like chemical bonds) makes this incomplete.​

Why (D) Prevails

Closed systems maintain constant mass while energy (as heat or work) crosses boundaries, enabling analysis via the first law: ΔU = Q – W.​