Figure 18.1 shows two ways to raise the temperature in a beaker of water: by heating with
a flame and by stirring vigorously with a spoon. Using the flame involves heat—energy in
transit because of the temperature difference between flame and water. But there’s no temperature
difference between spoon and water; here the energy transfer occurs because the
spoon does mechanical work on the water. We already know that doing work can increase
the kinetic or potential energy of a macroscopic object; here we see it, instead, changing
the internal energy associated ultimately with individual molecules. The point is that
both processes—heating and mechanical work—result in exactly the same final state—
namely, water with a higher temperature and therefore greater internal energy. It’s this
common result that made possible Joule’s quantitative identification of heat as a form of
energy (Fig. 18.2).
Connecting Your Knowledge
■ This chapter joins the concept of
work, introduced in Chapter 6 (6.1, 6.2),
and the behavior of ideal gases as
described in Chapter 17 (17.1).
■ You should have a clear understanding
of the conservation-of-energy
principle introduced in Chapter 7 (7.3).
18 Heat, Work, and the First
Law of Thermodynamics
New Concepts, New Skills
By the end of this chapter you should
be able to
■ Explain how the first law of thermodynamics
extends the conservation-ofenergy
principle to include thermal
energy (18.1).
■ Describe quantitatively the effects
of basic thermodynamic processes—
isothermal, adiabatic, isobaric, and
constant-volume—on an ideal
gas (18.2).
■ Determine the specific heat of an
ideal gas based on its molecular
structure (18.3).