Question

Statement - 1
Two vessels A and B are connected to each other by a stopcock. Vessel A contains a gas at $0^{o}C$ and 1 atmosphere pressure and vessel B is evacuated. The two vessels are thermally insulated from the surroundings. If the stopcock is suddenly opened, there will be no change in the internal energy of the gas.

Statement - 2
No transfer of heat energy takes place between the system and the surroundings.

• A. 1) Statement - I is true, Statement - II is true; statement - II is a correct explanation for statement - I
• B. 2) Statement - I is true, statement - II is true; statement - II is NOT a correct explanation for statement - I
• C. 3) statement - I is true, statement - II is false
• D. 4) statement - I is false, statement - II is true

Answer 1

The correct option is B 2) Statement - I is true, statement - II is true; statement - II is NOT a correct explanation for statement - I

Since the gas in vessel A expands freely, there will be no work done. Also, heat given to/from the system is zero hence from the first law of thermodynamics change in internal energy is zero.
The two vessels(as a system) are thermally insulated from the surroundings.

Statement - 2 is true.

Hence both statements are correct but the second statement is not the correct reason for the first