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other not.
The first law was not fully understood
until the second law was formulated by Clausius and Thomson in
the 1850's. Some twenty-five years earlier Carnot had observed
that like the fall of a stream that turns a mill wheel, it was
the "fall" of heat from higher to lower temperatures
that motivates a steam engine. That this work showed an irreversible
destruction of "motive force" or potential for producing
change suggested to Clausius and Thomson that either the first
law was false (energy was not conserved), or else energy was
not the motive force for change. Recognizing that the active
principle and the conserved quantity could not be the same they
realized that there were two laws at work and showed their relation.
Clausius coined the word "entropy" to refer to the
dissipated potential, and the second law states that all natural
processes proceed so as to maximize the entropy (or equivalently
minimize or dissipate the potential), while energy, at the same
time is entirely conserved. The balance equation of the second
law, expressed as
says that in all real world processes entropy
always increases (literally "the change in entropy is greater
than zero").
In Clausius' (1865, p. 400) words, the
two laws thus became: "The energy of the world remains constant.
The entropy of the world strives to a maximum," and with
this understanding, in sharp contrast to the "dead"
mechanical world of Descartes and Newton, the nomological basis
for a world that is instead active, and end-directed was identified.
Entropy maximization as Planck first recognized provides a final
cause, in Aristotle's typology, of all natural processes, "the
end to which everything strives and which everything serves"
or "the end of every motive or generative process"
(Bunge, 1979, p. 32).
The active nature of the second law is
intuitively easy to grasp and empirically easy to demonstrate.
Figure 2 shows a glass of hot liquid placed in a room at a cooler
temperature.The difference in temperatures
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| Figure 2. A glass
of liquid at temperature T(I) is placed in a room at temperature
T(II) so that T(I) is greater than T(II). The disequilibrium
produces a field potential that spontaneously drives a flow of
energy in the form of heat from the glass to the room so as to
drain the potential until it is minimized (the entropy is maximized),
at which time thermodynamic equilibrium is reached and all flows
stop. The expression refers to the conservation of energy in
that the flow from the glass equals the flow of heat into the
room. From Swenson (1991), p. 45. Copyright 1991 Intersystems
Publications. Adapted by permission. |
in the glass-room system constitutes a
potential and a flow of energy in the form of heat, a "drain"
on the potential, is produced from the glass (source) to the
room (sink) until the potential is minimized (the entropy is
maximized) and the liquid and the room are at the same temperature.
At this point, all flows and thus all entropy production stops
and the system is at thermodynamic equilibrium.
The same principle applies to any system where any form of energy
is out of equilibrium with its surrounds (e.g., whether mechanical,
chemical, electrical or energy in the form of heat), a potential
exists that the
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