A gas is confined to one side of a rigid, insulated container divided by a partition. The other side is initially evacuated. The following data are known for the initial state of the gas: P1 = 3 bar, T1 = 380 ^oK, and V1 = 0.025 m^3. When the partition is removed, the gas expands to fill the entire container and achieves a final equilibrium pressure of 1.5 bar. Assuming ideal gas behavior. Why is this process isothermal (T1=T2)? Derive equations justifying.