DS
ð Þ A!B þ ÀQ spon =T 0
À
Á
A!B
! 0
This total entropy growth or generation of the spontaneous transformation,
which is positive definite, is denoted by the shorthand notation, D G S
ð
Þ universe ,
DS
ð Þþ ÀQ spon =T 0
À
Á D G S
ð
Þ universe
ð126Þ
Consider a corresponding reversible event of the system reservoir (which now
includes a reversible component and a work reservoir) with the system undergoing
the same A ! B. The system entropy change, S(B) – S(A), remains the same, and
there is no entropy change in the reversible component and in the work reservoir.
The entropy change in the new reversible universe can be different from that in the
original universe, therefore, only if entropy change in the surrounding heat reservoir
DS 0
ð
Þ rev ¼ ÀQ rev =T 0
ð
Þ
as shown in Fig. 8.2, differs from that in Fig. 8.1
DS 0
ð
Þ spon ¼ ÀQ spon =T 0
À
Á
in the original universe of Fig. 8.1.
Fig. 8.2 The “universe” of a reversible event, in which the system undergoes managed change
between the same end states of the system as shown in Fig. 8.1
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8 The Second Law: The Entropy Growth Potential Principle …