Question

one litre of an ideal gas at a pressure of 10 atm expands isothermally into a vacuum until total volume is 10 litres. how much work is done in expansion?

Answer 1

In the case of expansion of any gas, work is done by the system.

We know that 
w=-P(ext)ΔV=-Pext(V2-V1)
where P(ext)=external pressure of the system=0

(The given pressure of 10atm in the question, is the pressure of gas itself.But we need external pressure in the expression. The gas is expanding into vacuum which has no pressure. Thus external pressure=0)

V2=10lit.
V1=1lit.

Thus work done by the system will be:
w=-Pext(V2-V1)
  =0(10-1)
  =0
Thus no work is done!