文档介绍：This is the Nearest One Head 669
PP UZZLERUZZLER
The purpose of a refrigerator is to keep
its contents cool. Beyond the attendant
increase in your electricity bill, there is
another good reason you should not try
to cool the kitchen on a hot day by
leaving the refrigerator door open.
What might this reason be?
(Charles D. Winters)
chapter
Heat Engines, Entropy, and the
Second Law of Thermodynamics
Chapter Outline
Heat Engines and the Second Heat Pumps and Refrigerators
Law of Thermodynamics Entropy
Reversible and Irreversible Entropy Changes in Irreversible
Processes Processes
The Carnot Engine (Optional) Entropy on a
Gasoline and Diesel Engines Microscopic Scale
669
670 CHAPTER 22 Heat Engines, Entropy, and the Second Law of Thermodynamics
he first law of thermodynamics, which we studied in Chapter 20, is a state-
ment of conservation of energy, generalized to include internal energy. This
Tlaw states that a change in internal energy in a system can occur as a result of
energy transfer by heat or by work, or by both. As was stated in Chapter 20, the law
makes no distinction between the results of heat and the results of work—either
heat or work can cause a change in internal energy. However, an important distinc-
tion between the two is not evident from the first law. One manifestation of this
distinction is that it is impossible to convert internal pletely to mechan-
ical energy by taking a substance through a thermodynamic cycle such as in a heat
engine, a device we study in this chapter.
Although the first law of thermodynamics is very important, it makes no dis-
tinction between processes that occur spontaneously and those that do not. How-
ever, we find that only certain types of energy-conversion and energy-transfer
processes actually take place. The second law of thermodynamics, which we study in
this chapter, establishes which processes do and which do