Question

How does the internal energy of the system change ?

• A. Increases
• B. Decreases
• C. Remains Same
• D. Cannot be predicted

Answer 1

The correct option is C Remains Same

The first law of thermodynamics states that:
$\delta Q=\Delta U+w=\Delta U+\int PdV$
The box is well insulated; hence the heat supplied to the gas is zero.
The work done is against the pressure of a vacuum. i.e. P = 0 Pa.
$\delta Q=\Delta U+\int PdV$
$\delta Q=0=\Delta U+0$
Change in internal energy is zero, hence the temperature of the body doesn't change.
The solution is independent of the type of gas, whether it is ideal or not.