Re: Entropy confusion, please help!


Uno Lapideus wrote:
Trying to explain entropy to kids, I find that I need some help with
understanding the concept... The second law of thermodynamics is
usually stated as "Heat (energy) flows from higher temperature
objects to lower temperature objects, until thermal equilibrium is
reached" (please correct me if I'm wrong here...), sometimes as
"in a closed system, entropy (a measure of disorder) will always
increase" and sometimes as "natural processes cause things to move
from improbable and unstable orderly states (less entropy) to probable
and stable disorderly states (more entropy)."


I have found that equating entropy with disorder can be very
confusing....so don't do it. Every process will be less than 100%
efficient, this is because some of the energy [or heat] that goes into
driving the process will be lost and is no longer available to do work.

A prime example is a car engine....burning gasoline creates a great
deal of energy, of which only about 25% is actually put into moving
that car forward. The rest is lost as wasted heat that goes out the
tailpipe, and is dissipated through the radiator and heats the air.
Other loses are due to friction causing waste heat in brakes and other
mechanical parts. All this wasted heat warms up the atmosphere,
increasing its entropy.

This rule is true for every process....nothing is free from the second
rule, it applies everywhere, all the time.

Ken


Now, for example, is not ice (water crystals) a "stable and
ordered" form, liquid water a a more random form, and steam the most
chaotic form, of H2O molecule "order"? I also remember reading
somewhere that "entropy is zero in an object that has no thermal
motion, such as a fictitious crystal at 0 K"...
This is where I find confusion: Since heat indeed flows from hotter to
colder objects , it seems to me that, at least in the water example,
entropy goes from higher to lower... And if "absolute zero" is
where we find the highest form of order (zero entropy), isn't
universal entropy running from maximum disorder (big bang, with its
very high temperature) towards minimum disorder (the absolute zero
"heat death" of a completely "run dowm" Universe)?
Intuitively, I think of the atoms in a white-hot piece of iron as
"moving more randomly" than does the atoms in a piece of iron that
has been in a freezer for a few days. Likewise, I think of the state of
affairs immediately following the "big bang" as a whole lot more
chaotic than the absolute thermal uniformity of a Universe that, some
time far in the distant future, has reached "absolute equilibrium"
Obviously, my thinking is flawed. Can someone please help me get this
entropy stuff straight?
Many thanks in advance,
Uno

.

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