An ideal gas is allowed to expand against a constant pressure of 2 bar from 10 L to 50 L in one step. Calculate the amount of work done by the gas. If the same expansion were carried out reversibly, will the work done be higher or lower than the earlier case? (Given that 1 L bar = 100 J)
In the first case, as the expansion is against constant external pressure,
W = ${- p }_{ ext }$(V2-V1)
= -2 bar x (50-10)L
= -80 L bar = -80 x 101 J
= -8kJ( 1kJ bar = 101 J)
If the above expansion were carried out reversibly, the internal pressure of the gas should be infinetisinally greater than the external pressure at every stage. Hence, the work done will be more.