# 10 moles of an ideal gas expands into vacuum. The work done is

(a) infinity
(b) 10 J
(c) zero
(d) 5 J

If an ideal gas expand against vacuum, the irreversible expansion is called free expansion.
As $P_{ext} = 0$, therefore, for reversible as well as irreversible expansion, work done = 0
$W_{irre} = -P_{ext}\Delta V = 0\times \Delta V=0$