There are two identical chambers, completely thermally insulated from… | JEE Main 2013 (9 Apr, Shift 1)

Q238JEE Main 2013 · 9 APR · SHIFT 1Medium

Thermodynamic Processes

There are two identical chambers, completely thermally insulated from surroundings. Both chambers have a partition wall dividing the chambers in two compartments. Compartment 1 is filled with an ideal gas and Compartment 3 is filled with a real gas. Compartments 2 and 4 are vacuum. A small hole (orifice) is made in the partition walls and the gases are allowed to expand in vacuum. Statement - 1: No change in the temperature of the gas takes place when ideal gas expands in vacuum. However, the temperature of real gas goes down (cooling) when it expands in vacuum. Statement - 2: The internal energy of an ideal gas is only kinetic. The internal energy of a real gas is kinetic as well as potential.

Show answer and solution

Answer: (b)

Free expansion into vacuum in an insulated chamber: $Q = 0$ , $W = 0$ , so $\Delta U = 0$ .
Ideal gas: $U$ is only kinetic, so $U$ constant means $T$ constant.
Real gas: $U =$ KE + PE. On expansion molecules move apart against attraction, PE increases, so KE (and $T$ ) falls.
Both statements are true and Statement-2 explains Statement-1.
So the answer is (b).

Report a mistake

Thermodynamic Processes question from JEE Main 2013 (9 Apr, Shift 1)

More questions on Thermodynamic Processes