Entropy And The Second law of Thermodynamics :
We can imagine many processes that never happen; even they do not
violate the law of conservation of energy. For instant, hot coffee resting in a
mug might give up some internal thermal energy and spontaneously began
to rotate.
Entropy is a thermodynamic property that can be used to
determine the energy not available for work in a thermodynamic process, such
as in energy conversion devices, engines, or machines. Such devices can only be
driven by convertible energy, and have a theoretical maximum efficiency when converting
energy to work. During this work, entropy accumulates in the system, which then dissipates in the form of waste heat.
Thermodynamics is the branch of physical
science concerned with heat and its relation to other forms of energy
and work. It defines macroscopic variables, that describe average
properties of material bodies and radiation, and explains how they are related
and by what laws they change with time.
Thermodynamics does not describe the microscopic constituents of
matter, and its laws can be derived from statistical mechanics.
For thermodynamics and statistical thermodynamics to apply
to a process in a body, it is necessary that the atomic mechanisms of the
process fall into just two classes: those so rapid that, in the time frame of
the process of interest, the atomic states effectively visit all of their
accessible range, and those so slow that their effects can be neglected in the
time frame of the process of interest.The rapid atomic mechanisms mediate the
macroscopic changes that are of interest for thermodynamics and statistical
thermodynamics, because they quickly bring the system near enough to
thermodynamic equilibrium.
"When intermediate rates are present, thermodynamics
and statistical mechanics cannot be applied."
The intermediate rate atomic processes do not bring the
system near enough to thermodynamic equilibrium in the time frame of the
macroscopic process of interest. This separation of time scales of atomic
processes is a theme that recurs throughout the subject.
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