Thermodynamics Historical Synopsis

“flow” of heat from a high
temperature to a low temperature. Eighteenth-century engineers
knew that with cleverly designed machinery, this heat flow could be
used in a “heat engine” to produce useful workoutput.
The basic premise of the caloric theory was that heat was
“conserved,” meaning that it was indestructible and uncreatable;
that assumption served well the pioneers in heat theory, including
Sadi Carnot, whose heat engine studies begin our story of
thermodynamics. But the doctrine of heat conservation was attacked
in the 1840s by Robert Mayer, James Joule, Hermann Helmholtz, and
others. Their criticism doomed the caloric theory, but offered little
guidance for construction of a new theory.
The taskof building the rudiments of the new heat science,
eventually called thermodynamics, fell to William Thomson and
Rudolf Clausius in the 1850s. One of the basic ingredients of their
theory was the concept that any system has an intrinsic property
Thomson called “energy,” which he believed was somehow
connected with the random motion of the system’s molecules. He
could not refine this molecular interpretation because in the mid–
nineteenth century the structure and behavior—and even the
existence—of molecules were controversial. But he could see that
the energy of a system—not the heat—was conserved, and he
expressed this conclusion in a simple differential equation.
In modern thermodynamics, energy has an equal partner called
“entropy.” Clausius introduced the entropy concept, and supplied
the name, but he was ambivalent about recognizing its fundamental
importance. He showed in a second simple differential equation
how entropy is connected with heat and temperature, and stated
formally the law now known as the second law of thermodynamics:
that in an isolated system, entropy increases to a maximum value.
But he hesitated to go further. The dubious status of the molecular
hypothesis was again a concern.Thermodynamics had its Newton: Willard Gibbs. Where Clausius
hesitated, Gibbs did not. Gibbs recognized the energy-entropy
partnership, and added to it a concept of great utility in the study of
chemical change, the “chemical potential.” Without much guidance
from experimental results—few were available—Gibbs applied his
scheme to a long list of disparate phenomena. Gibbs’s masterpiece
was a lengthy, but compactly written, treatise on thermodynamics,
published in the 1870s.
Gibbs’s treatise opened theoretical vistas far beyond the theory of
heat sought by Clausius and Thomson. Once Gibbs’s manifold
messages were understood (or rediscovered), the new territory was
explored. One of the explorers was Walther Nernst, who was in
search of a theory of chemical affinity, the force that drives chemical
reactions. He found his theory by taking a detour into the realm of
low-temperature physics and chemistry.