More I think about it more I am convinced that W in
deltaU=Q+W
meant to be "mechanical energy" and not "work." Was a
linguistic trap (or poor translation from another language)
responsible for "work" somewhere along the line? People
who developed thermodynamics were smart, they knew
that all three terms must be energies. That is why this
formula was named the "energy conservation" law.
Consider the old pedagogical Carnot engine in which grains
of sand are shifted horizontally from-or-to the piston as it
moves very slowly from "floor to floor" and back. What is
W? It is deltaPEgrv of the sand during one cycle. Somebody
(?) referred to it (a slip of the tongue) as "work" because
potential energy is DEFINED as "work done against weight",
not because "work is a form of energy." How did "ability to
do work" became "work". Yes, deltaPEgrv=m*g*h (where
h is the mean elevation) Yes, deltaPEgrv=the loop area in
the p-V diagram. No, work is not a "form of energy."
The verbal part of the heat engine vocabulary clearly states
that what comes in (thermal energy from the hot reservoir)
is SPLIT into two flows: thermal and the other. If what is
split into two parts is energy then each part must also be
energy. This was so obvious that nobody bothered to
nitpick. Perhaps "energy is the ability to do work" was
somehow abbreviated by "work is energy".
When I move a heavy box to a higher elevation its potential
energy is increased by PE=m*g*y. The chemical energy
CE lost by my body CE = QE + PE = QE + m*g*y. But
the absolute value of the work done by mg is also m*g*y.
It is tempting to say CE=QE+W instead of CE=QE+PE.
Ludwik Kowalski
Those who know will know, those who are confused
deserve to be confused. That is not what I would say.