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

Explanation

Work done of a gas in vacuum, `W = -p_('ext") (V_(2) - V_(1))`. As `p_("ext") = 0` so `W = - 0 (5 - 1) = 0` As internal energy of an ideal gas depends only on temperature, therefore, for isothermal expansion of an ideal gas, internal energy remains constant.
i.e., `Delta U = 0`
It is to be remember that as `H = U + PV, Delta H = (U + pV) = Delta U + p Delta V = Delta U + nR (Delta T)`. For isothermal process. `Delta T = 0` and also `Delta U = 0`, as stated above, therefore, `Delta H = 0`