4 . 0   L of an ideal gas is allowed to expand isothermally into vacuum until the total volume is 20   L . The amount of heat absorbed in this expansion is L atm.

Step-by-step solution

In case of expansion, work is done by system. Now, as we know that, W = - P ext .   ∆ V As the gas is expanding into vacuums which has no pressure, i.e., P ext . = 0 ∴   W = 0 Hence, no work is done. From first law of thermodynamics, ΔU = q + W As the system is working at constant temperature, i.e., isothermally. ∴ ΔU = 0 Hence q = - W = 0