The process can be shown graphically as in Fig 21.2 and the area under the curve is the work done by the gas.
Fig 21.2 Reversible and irreversible expansions of an ideal gas. The smooth curve corresponds to a reversible process and the dashed lines represent an irreversible process.
This slow reversible expansion takes an infinitely long time to occur. A three step sequence is shown in Fig 21.2 . The area under the dotted lines is the work done by the gas in the irreversible expansion of the gas.
w irr = PC (V C - V 1 ) + PD (V D - V C ) + PE (V 2 - V D )
