Download HOMEWORK #2

HOMEWORK #2
Name: _______________________
Date: ___________ Period: _____
Heat Engine and Entropy
THE LAWS OF THERMODYNAMICS
1st: Energy can be transformed (changed from
one form to another), but it can neither be
created nor destroyed.
2nd: In a system, a process that occurs will tend
to increase the total entropy of the universe.
(Heat will not of itself flow from cold to hot.)
REVIEW QUESTIONS – check concepts
1. What is the meaning of the Greek words
from which we get the word thermodynamics?
2. What is the lowest possible temperature on
the Celsius scale? On the Kelvin scale?
(PHYZR#12)
(PHYZR#12)
3. How does the law of conservation of energy
relate to the first law of thermodynamics?
4. What is the relationship between heat flow
input, work done, and heat flow output?
(Page#4)
(Page#4)
5. What is the physicist’s term for a measure of
disorder (messiness)? (PHYZR#14)
6. With respect to orderly and disorderly states,
what do natural system tend to do? (PHYZR#14)
7. Can a disorderly state ever transform to an
orderly state? Explain. (Page#6)
8. Is a melting ice cube an example of
increasing order or decreasing order? (Page#6)
HEAT ENGINE PROBLEMS
9. Use conservation of energy to determine the missing energy.
20 J
50 J
200 J
10 J
200 J
80 J
900 J
700 J
Fremont Physics ©Kepple 2012
40 J
100 J
600 J
120 J
70 J
20 J
34 J
12 J
Thermodynamics – HW-B
1/11/13
PLUG AND CHUG – using equations
10. An engine absorbs 300 J of heat and
exhausts 200 J. How much work is done?
11. A heat engine does 50 J of work with 250 J
of exhaust. How much heat was absorbed?
12. How much heat is ejected each cycle by a
heat engine that does 60 J of work in each cycle
and absorbs 90 J of heat in each cycle?
13. If a heat engine does 100 J of work in each
cycle and ejects 125 J in each cycle, how much
heat has to be added in each cycle?
THINK AND EXPLAIN – critical thinking
14. Pretend you place a cup of hot coffee in your refridgerator and the coffee absorbs 10 J of energy
from the refridgerator and becomes warmer, while the refridgerator gives up 10 J of energy and
becomes colder. Would this energy transfer violate the first law of thermodynamics? Would this
energy transfer violate the second law of thermodynamics? Explain.
15. Water put into the freezer compartment in your refrigerator goes to a state of less molecular
disorder when it freezes. Is this an exception to the entropy principle? Explain.
16. What is the connection between entropy and time? Explain how you can tell the difference
between the past and the future by using entropy.