文档介绍：22
Heat Engines, Entropy, and the
Second Law of Thermodynamics
CHAPTER OUTLINE ANSWERS TO QUESTIONS
Heat Engines and the
Second Law of First, the efficiency of the automobile engine cannot exceed the
Thermodynamics Carnot efficiency: it is limited by the temperature of burning
Heat Pumps and
Refrigerators fuel and the temperature of the environment into which the
Reversible and Irreversible exhaust is dumped. Second, the engine block cannot be
Processes allowed to go over a certain temperature. Third, any practical
The Carnot Engine engine has friction, plete burning of fuel, and limits set
Gasoline and Diesel Engines by timing and energy transfer by heat.
Entropy
Entropy Changes in
Irreversible Processes It is easier to control the temperature of a hot reservoir. If it
Entropy on a Microscopic cools down, then heat can be added through some external
Scale means, like an exothermic reaction. If it gets too hot, then heat
can be allowed to “escape” into the atmosphere. To maintain
the temperature of a cold reservoir, one must remove heat if
the reservoir gets too hot. Doing this requires either an “even
colder” reservoir, which you also must maintain, or an
endothermic process.
A higher steam temperature means that more energy can be extracted from the steam. For a
constant temperature heat sink at Tc , and steam at Th , the efficiency of the power plant goes as
TThc− Tc
=−1 and is maximized for a high Th .
Th Th
No. Any heat engine takes in energy by heat and must also put out energy by heat. The energy that
is dumped as exhaust into the low-temperature sink will always be thermal pollution in the outside
environment. So-called ‘steady growth’ in human energy use cannot continue.
No. The first law of thermodynamics is a statement about energy conservation, while the second is a
statement about stable thermal equilibrium. They are by no means m