Chemistry · Thermodynamics · NEET
The only thing that changes is what can cross the boundary. Open system: BOTH matter and energy can cross (an open beaker of boiling water loses steam and heat). Closed system: ONLY energy can cross, matter is trapped (a sealed steel flask on a burner gains heat but no gas escapes). Isolated system: NEITHER matter nor energy can cross (an ideal thermos flask). So the ladder is: open = both, closed = energy only, isolated = none. For NEET, remember matter escaping is the strongest clue for 'open'.
A thermos flask (or any closed, insulated vessel) is treated as an ISOLATED system in NCERT. It is sealed, so matter cannot leave, and it is insulated, so heat cannot flow in or out. So neither matter nor energy crosses the boundary. In real life a thermos is not perfect (drinks slowly cool), but NEET treats the ideal thermos as isolated. NCERT gives this exact example.
Yes. A closed system CAN exchange energy (heat and work), it just cannot exchange matter. This is the point students miss. Example: reactants sealed in a closed copper or steel vessel. The copper conducts heat, so energy flows in or out, but the walls are sealed so no gas escapes. Closed does NOT mean 'nothing can enter or leave' — it only blocks matter.
Both trap matter (nothing material enters or leaves in either one). The difference is energy. A closed system lets energy pass (its walls conduct heat, like copper or steel). An isolated system blocks energy too (its walls are insulated, like a thermos). So: closed = matter blocked, energy free; isolated = matter blocked, energy blocked. Same sealed vessel, but change the wall from conducting to insulating and closed becomes isolated.
The human body is an OPEN system. It takes in matter (food, water, oxygen) and gives out matter (CO2, sweat, waste). It also exchanges energy as heat. Because BOTH matter and energy cross the boundary, it is open. A useful rule: any living thing that eats and breathes is an open system.
Ask two yes/no questions about the boundary. Q1: Can matter cross? Q2: Can energy cross? If matter YES (and energy YES) → open. If matter NO but energy YES → closed. If matter NO and energy NO → isolated. Look for keywords: 'open vessel' or steam/gas escaping = open; 'sealed conducting/copper/steel' = closed; 'sealed and insulated' or 'thermos' = isolated.
Two moles of an ideal gas undergo free expansion from 10 L to 100 L at 300 K. The values of ΔS(system) and ΔS(surroundings) are (R = universal gas constant):
At a certain temperature T (K), during a process, 500 J is absorbed by the system and work of 200 J is done by the system. Then the change in internal energy of the system is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Open, closed and isolated. They differ only in what crosses the boundary: open exchanges both matter and energy, closed exchanges only energy, isolated exchanges neither.
Open: an open beaker of boiling water (steam and heat leave). Closed: reactants sealed in a copper or steel vessel (heat flows, matter cannot). Isolated: reactants in a thermos flask (no heat, no matter cross).
Because both matter and energy leave the boundary. Steam (matter) escapes into the air and heat (energy) also flows out. When both cross, the system is open.
The boundary walls. Sealed but conducting walls give a closed system (energy passes, matter cannot). Sealed and insulated walls give an isolated system (nothing passes). Open walls give an open system.
For an isolated system the surroundings exchange no heat, so ΔS(surroundings) = 0. This is exactly why free expansion in an insulated container gives ΔS(surr) = 0, a common NEET point.
