Geology Reference
In-Depth Information
Chapter 2
Thermodynamics
2.1 General
Thermodynamics is the theory of the interaction of heat and work and of their
relationship to the physical properties and processes in material systems, dealt with
at the macroscopic scale. One of its principal uses is therefore to provide con-
straints on the constitutive equations that describe the state of systems or the
processes occurring in them. The foundation of thermodynamics consists of a
minimal number of postulates or empirical laws drawn from experience. However,
it has also been proposed that it can be regarded as being rooted in some universal
and fundamental concepts of symmetry or invariance under transformation that
apply to physical laws (Callen
1974
). The scope of thermodynamics has tradi-
tionally been limited mainly to systems in equilibrium but has more recently been
extended to deal also with non-equilibrium situations. We shall give here a brief
summary of the principal results of these two branches of the theory.
2.2 Equilibrium Thermodynamics
We first recall the elements of classical equilibrium thermodynamics (or ther-
mostatics). We take the concepts of heat Q and work W to be understood from
classical physics or physical experience. However, because of path dependences,
these quantities are inadequate for the proper description of the state of a physical
system at any instant, for which further concepts are required (for general texts, see
Callen
1960
; Denbigh
1971
; Guggenheim
1985
; Callen
1985
; for general texts, see
Pippard
1957
).
Thermodynamics therefore begins with the introduction of the macroscopic
concept of the energy of a system, which is defined in terms of its conservation,
through
the
First
Law,
as
function
of
state
called
the
internal
energy
U.
