by Equation 2.11. As illustrated in Figure 2.8b, the opposite is true for the
compression process; the reversible process requires the minimum work.
As an illustration of a nanoscale scale process involving a reversible
compression, let’s consider a two-dimensional monolayer composed of
insoluble molecules (such as dodecanol) floating on the surface of water.
The two-dimensional monolayer can be compressed using barriers
(Figure 2.9). In this case, we replace volume by area (A) and pressure
State A (reversible)
State A
(reversible)
State A
(irreversible)
State A
(irreversible)
Pressure
Final state B
Final state B
P i
P f
Pressure
P i
P f
V i
V f
Volume
V i
V f
Volume
(a)
(b)
Figure 2.8 Graphical representations comparing the reversible and irreversible
path for (a) expansion and (b) compression processes. The shaded areas represent
the total work done for the corresponding process. Reversible expansion gives the
maximum work, while reversible compression gives the minimum work.
THE FIRST LAW OF THERMODYNAMICS
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