Chronology | Current Month | Current Thread | Current Date |
[Year List] [Month List (current year)] | [Date Index] [Thread Index] | [Thread Prev] [Thread Next] | [Date Prev] [Date Next] |
Aaaiiieeee! Is this is yet another attempt to re-define "heat"????
1) Once upon a time, everybody used "heat" to mean "thermal energy".
2) Then there was an attempt to re-define it to mean "energy transfer
due to a difference in temperature".
in3) Now apparently there is an attempt to re-define it to mean "change
enthalpy"????
I think this is a step in the wrong direction.
This works nicely for constant-pressure
processes when no "other" work (besides compression/expansion work)
is being done. By and large, I think they've made the right
decision, given their audience and the scope of their book.
I haven't read the book. But judging from the reports on this list,
they've paid a terrible price for little (if any) gain.
weThere are >>just too many processes where Q is not equal to Delta-H, so
need separate names for the two quantities.
theMaybe we ought to listen
and find some way to improve the language for generations to come. I've
tried to re-write some of my labs with this injunction in mind, and it is
_hard_. It is one thing to object to current language usage, and quite
another to propose acceptable alternatives. I need help with the latter.
As I have said before, there are two issues here; a big issue and a small
issue. The definition of the word "heat" and other language details are
tremendous_small_ issue. The much larger issue is conceptual.
The big conceptual blunder is the over-emphasis on "energy transfer due to
a difference in temperature". It's really quite secondary to a modern
understanding of thermodynamics. Focusing thereon puts you at a
disadvantage when discussing situations where thermal energy is being
_created_ not just transferred:
asTo the modern way of thinking:
0) The zeroth law of thermodynamics states that there is such a thing
thermal equilibrium. In equilibrium, objects have the same
temperature. This is true and important.
1) The first law of thermodynamics states that energy is conserved. In
particular, energy obeys a _local_ conservation law. This is the first
law; nothing more, nothing less. This is true and important.
2) The second law of thermodynamics states that entropy obeys a local
law of nondecrease. This is true and important.
3) The third law of thermodynamics alleges that the entropy of some
things goes to zero as temperature goes to zero. This is true except when
it's not true. It's not very important.
4) Entropy is defined in terms of statistics. It is well defined even
when the temperature is unknown, irrelevant, or zero. This is true and
important.
Note that the word "heat" does not appear in the foregoing laws. Getting
the big picture does not require worrying about the exact definition of
"heat".
Moving now from the large issue to the small issue: Once you have some
semblance of a modern understanding of thermodynamics, there is no harm in
using "heat" as a noun, in just the way it was used by Rumford in 1798 and
is still used by respectable experts today.
Some partisan neologists claim that anyone who uses "heat" as a noun must
adhere to the caloric theory that Rumford discredited. It is tiresome to
hear such a preposterous accusation repeated so often.
I just got back from a three-day symposium in honor of Richardson, Reppy,
and Lee. It was, among other things, a reunion of most of the people who
had ever worked in the low-temperature physics lab at Cornell. These are
people who teach undergrads in the morning and do thermodynamics research
in the afternoon. They build refrigerators that will get down to
milliKelvin or microKelvin temperatures.
wouldI assure you that these people use "heat" as a noun. They talk about heat
pulses, heat capacity, heat leaks, heat shields, heat switches, and heat
exchangers. If you tried to tell them that "heat" is not a noun they
think you were from the far side of Mars.
To summarize: My advice is to keep your eye on the ball. Energy is
important! Entropy and temperature are important!
the(Energy transfer due to temperature differences is only a minor part of
larger picture.)