question_answer 1)

  Expansion of a gas in vacuum is called free expansion. Calculate work done and the change in internal energy when 1 litre of ideal gas expands isothermally into vacuum until its total volume is 5 litre.

Answer:

  In free isothermal expansion, external pressure is zero hence work will also be zero. \[w=P\Delta V=0\] \[\Delta U=0\]for all isothermal processes.