Consider two processes on a system as shown in the figure.

The volumes in the initial states are the same in the two processes and the volumes in the final states are also the same. Let ΔW₁ and ΔW₂ be the work done by the system in the processes A and B respectively.

Given V₁=V₂

We know that,

Work done = force ×displacement

Volume = area ×displacement

Therefore,

Work done=pressure ×volume

Let change in the volume of system = ΔV = V₂-V₁

Pressure =P

Thus, work done by the system W

ΔW=PΔV

For process A ΔW₁=P₁ΔV₁

For process B ΔW₂=P₂ΔV₂

Since ΔV₁=ΔV₂ we can write,

P₁ < P₂ (from graph)

Therefore ΔW₁ < ΔW₂.