Page 92 - Essentials of physical chemistry

54 Essentials of Physical Chemistry

FIGURE 4.1 Count Rumford, Benjamin Thompson (1753–1814). (Courtesy of the Chemical Heritage
Foundation.)

with no moving parts. The manufacture merely required boring a cylindrical hole with a large
cutting tool. Thompson showed that during the boring with a dull cutting tool, cold water in contact
with the cannon could be brought to a boil due to the heat generated by the boring process. He noted
that the heat released was proportional to the amount of work done on the cannon rather than the
amount of material removed, which would limit the amount of caloric released and there was no
mass change due to the release of ‘‘caloric.’’ A key aspect of his analysis was when he used a very
dull cutting tool to continually rub inside an unfinished bore hole for hours without further cutting.
It became clear that the work against the resistive friction caused the heat since no cutting was
releasing any possible ‘‘caloric.’’ On a personal basis Thompson was a person curious about
astronomy and other natural philosophy, so he used logic to formulate the connection between
heat and work. This change in interpretation brought about a connection between the mysterious
nature of heat and the more easily quantified concept of work. Count Rumford was a scientist of his
times remaining interested in astronomy, inventing an improved fireplace, and writing further
regarding the nature of flames and heat. His work is generally considered a breakthrough in the
formulation of thermodynamics because while heat certainly flows like a fluid you cannot capture
it in a bottle. Perhaps the mystery of the nature of heat is what still makes thermodynamics
challenging for students?
We need to define some terms so pay attention to the verbal meanings and the algebraic sign
conventions. While thermodynamics requires thoughtful reasoning, the level of required mathemat-
ics is relatively low and the computations are usually easy. Thermodynamics requires a type of
reasoning that is light in terms of mathematics but requires considerable use of logic.

DEFINITIONS

‘‘The system’’ is a region around some mechanical or biological device surrounded by an imaginary
boundary, mainly as an attention focusing region or bookkeeping device to define ‘‘inner’’ and
‘‘outer.’’ Ultimately, the ‘‘system’’ is the entire universe but thermodynamics can be used to focus
on a machine or localized region relative to some thermal boundary, which defines a region of
interest. An example would be a thermos bottle or a Dewar flask. The intention of a thermos bottle is
to provide a boundary wall against heat flow and experiments could be done within the thermos as
isolated from the ‘‘outside world,’’ but eventually heat will leak across that boundary relative to
conditions in the universe so time is involved to a degree. Again, we will analyze the events in an
internal combustion engine where the chemistry of the combustion is much faster than heat can flow