1.1 What is thermodynamics?
Thermodynamics is the science which has evolved from the original investigations
in the 19th century into the nature of \heat." At the time, the leading
theory of heat was that it was a type of fluid, which could flow from a hot body
to a colder one when they were brought into contact. We now know that what
was then called \heat" is not a fluid, but is actually a form of energy { it is
the energy associated with the continual, random motion of the atoms which
compose macroscopic matter, which we can t see directly.
This type of energy, which we will call thermal energy, can be converted
(at least in part) to other forms which we can perceive directly (for example,
kinetic, gravitational, or electrical energy), and which can be used to do useful
things such as propel an automobile or a 747. The principles of thermodynamics
govern the conversion of thermal energy to other, more useful forms.
For example, an automobile engine can be though of as a device which rst
converts chemical energy stored in fuel and oxygen molecules into thermal energy
by combustion, and then extracts part of that thermal energy to perform
the work necessary to propel the car forward, overcoming friction. Thermodynamics
is critical to all steps in this process (including determining the level of
pollutants emitted), and a careful thermodynamic analysis is required for the
design of fuel-ecient, low-polluting automobile engines. In general, thermodynamics
plays a vital role in the design of any engine or power-generating plant,
and therefore a good grounding in thermodynamics is required for much work
in engineering.
If thermodynamics only governed the behavior of engines, it would probably
be the most economically important of all sciences, but it is much more than
that. Since the chemical and physical state of matter depends strongly on how
much thermal energy it contains, thermodynamic principles play a central role
in any description of the properties of matter. For example, thermodynamics
allows us to understand why matter appears in di erent phases (solid, liquid,
or gaseous), and under what conditions one phase will transform to another.
The composition of a chemically-reacting mixture which is given enough time
to come to \equilibrium" is also fully determined by thermodynamic principles
(even though thermodynamics alone can t tell us how fast it will get there). For
these reasons, thermodynamics lies at the heart of materials science, chemistry,
and biology.