Expansion of gas in a vacuum is called free expansion. Calculate the work done and the change in internal energy when 1 litre of ideal gas expands isothermally into a vacuum until its total volume is 5 litre?
o Work done in vacuum is calculated by :
-w = Text (Vinitial - Vfinal )
For the given problem: Pext = 0, because it is a free expansion.
Hence –w = 0x(5-1) = 0.
o For an isothermal expansion, no heat will be absorbed or evolved, hence q=0
By the 1st law of thermodynamics ,
q = ∆U + (-w)
since , both w and q =0 , then the change in internal energy ∆U will also be 0.