83Chapter 9The Concept of Energy
In the last chapter, we showed how the concept of the atom, which has
proven so valuable to physicists, was developed basically by chemists.
The concept of energy to be dealt with here is another concept playing a
central role in physics, which was developed partially through the efforts
of the chemists, further illustrating the point that the division between
physics and chemistry is arbitrary.
The concept of energy has always been associated with the idea of
its conservation. The origins of this idea most likely originated with
the conservation of mass implicit in Newton’s equations of motion.
This assumption was strictly limited to mechanical reaction for it
was thought that for certain chemical reactions, such as burning, mass
was not conserved. This misconception was due in part to a lack of
an understanding of the process of oxidation, which was thought of
as a process whereby the burning object released a substance called
phlogiston, a word derived from ancient Greek, which meant “burning
up” and in turn was derived from the ancient Greek word phlox, which
meant fire. The theory first postulated by Johann Joachim Becher in 1667
postulated that phlogiston had a negative weight to account for the fact
that the products of combustion were heavier than the original substance,
which burned. Lavoisier on the other hand, correctly believed that
burning was due to the oxidation of the burning substance and that the
increase in weight was due to the weight of the oxygen that combined
with the burning substance. He proved this by carrying out oxidation in a
completely closed system and showed that the total amount of mass
before and after combustion was the same. He therefore postulated the
conservation of matter held for all reactions including both chemical and
mechanical ones.
Lavoisier’s conservation of mass did not, however, lead directly to
the conservation of energy but provided a model for it. It also provided