The figure shows three thermodynamic systems labelled (a), (b) and (c). System (a) is an open beaker, (b) is a sealed conducting vessel, and (c) is a sealed thermally insulated flask. Which system permits exchange of **energy but not matter** with its surroundings?   
A(a) only
B(b) only
C(c) only
DBoth (b) and (c)
Answer & Solution
Correct answer: B. (b) only
By definition, a **closed** system exchanges energy but not matter — that is system (b), the sealed conducting vessel: the seal blocks matter, but the conducting walls allow heat transfer. System (a) is **open** (both matter and energy cross the boundary). System (c) is **isolated** (neither crosses). So only (b) qualifies.
Related questions
Which of the following is a reversible process in the thermodynamic sense?A refrigerator extracts 600 J from the cold compartment and rejects 800 J to the room. ItsFor an ideal gas the adiabatic equation linking pressure and volume is:A Carnot engine operates between 400 K and 300 K. If it absorbs 800 J from the hot reservoThe change in internal energy of an ideal gas (γ = 1.4) when 2 moles are heated from 300 KThe second law of thermodynamics can be stated as: no engine can convert into work:The Carnot engine's efficiency between source temperature T₁ (hot) and sink T₂ (cold) is:An ideal gas at temperature T₁ is expanded adiabatically. Its final temperature T₂ is: