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partitioning dU & the first law (short)



Gang,

I must really be procrastinating on phys-L this week. Apologies to all who
have grown weary and wish I'd shut-up; but Ludwik a few weeks ago wanted
phys-L to be spiced-up.

Is the partitioning of dU into DQ and DW for a specific process unique?

I'm treating the above as short-hand for the partitioning of Delta_U into
sum of DQ's and W for a specific quasi-static process.

Opinion A: yes it is unique within certain proviso's. This is my current and
apparently lonely position.

Opinion B: no, its arbitrary how we partition Delta_U

Digression:

The first law is usually presented in the introductory books as follows:

For any quasi-static process connecting two equilibrium states, the
difference in the internal energy of the two states may be calculated as
follows:

U_f - U_i = sum of Dq's - W

Any path may be used to calculate Delta U, and in that sense and that sense
only I don't quibble with the idea of the partitioning being arbitrary. But
for a specific quasi-static path, I do quibble.

One can use this arbitrariness to compute Delta U for a non-quasi-static
process as long as the final and initial states are equilibrium states and
you can come up with a hypothetical quasi-static process that connects the
two states.

The above statement of the first law explicitly relates equilibrium states
and therefore, as presented, is in the realm of equilibrium thermodynamics.
Are there any folks knowledgible in the ways of non-equilibrium
thermodynamics who can shed light on what adjustments must be made regarding
meaning and interpretation of the 1st law in non-equilibrium thermodynamics?

More thoughts later.

Joel Rauber
Joel_Rauber@sdstate.edu