CP Major Test Chapter 24: Thermodynamics

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2.26

Short Answer (120)

Answer the questions below on your own paper. Be sure that each part of each answer is in a complete sentence. Be sure your answers are done clearly in ‘a’, ‘b’, ‘c’ bulleted format. Answer each numbered question on its own page. DO NOT put more than one numbered answer on a page.

1. Consider the first law of thermodynamics

a) State this law in terms of the law of conservation of energy.

b) State this law in terms of adiabatic processes

c) According to this law what must happen to the temperature of this classroom when a cup of hot coca cools?

d) According to this law what happens to the temperature of the air in this room when ice melts in a cup of ice water?

2. Consider a heat engine as pictured below.

Draw this diagram on your own paper and in place of the letter put the correct term on or nearby the part of the engine that applies to that term.

Low temperature reservoir

Work done

Heat input

High Temperature reservoir

Heat output

3. Consider a refrigerator. A refrigerator removes energy as heat from its insides.

a) What does the refrigerator do with this energy as heat?

b) A typical refrigerator might extract 1000 Joules of energy from its insides but by doing so it has to get rid of 1500 Joules of energy. What is the source of the additional 500 J?

c) Why is it a bad idea to cool your kitchen by leaving the refrigerator door open?

PART III True/False (30)

Indicate whether the statement is true or false. Mark your answer document ‘A’ for true and ‘B’ for false.

PART IV Rewrite (60)

On your own paper rewrite the false statements so that they will be true. Be sure to address all of the areas of the false statement that are false. You will receive ten (10, 5+5, X) points for each correctly rewritten statement. Do NOT copy the false statements nor is it necessary to rewrite the true statements.

4. The study of thermodynamics is primarily concerned with subatomic systems.

5. According to the first law of thermodynamics whenever heat is added to a system, it transforms to a greater amount of some other form of energy.

6. Adiabatic process must happen very slowly.

7. The second law of thermodynamics states that energy must always go from where it is hot to where it is cold

8. A heat engine, no matter how efficient, cannot ever convert all of its thermal energy into work.

9. As air rises it expands adiabatically and gets very hot; as air descends it contracts adiabatically and it cools.

10. One way or another every engine is a heat engine and every heat engine uses energy to do work and in the process create useless energy as heat.

11. According to the second law of thermodynamics entropy must always decrease when work is done.

12. The only way for a heat engine to be 100% efficient is if the cold temperature is absolute zero; since it is impossible to reach this temperature it is impossible for a heat engine to be 100% efficient.

13. A very good way to defining entropy is to define it in terms of the ability to do work; systems of high entropy can do more work then systems that have low entropy.

PART V: Multiple Choice (51)

Identify the choice that best completes the statement or answers the question.Carefully place your answer choice on your answer document.

14. What kind of scale is the study of thermodynamics concerned with?

a.	subatomic scale	c.	microscopic scale
b.	macroscopic scale	d.	all scales

15. The first law of thermodynamics is really a statement of which law?

a.	The law of conservation of energy	c.	Newton’s law of universal gravitation
b.	Newton’s first law	d.	Boyle’s law

16. At what temperature does an object have absolutely no energy as heat?

a.	32 degrees Fahrenheit	c.	Zero Kelvins
b.	Zero degrees Celsius	d.	100 Kelvins

17. Which law of thermodynamics states that when two objects are in thermal equilibrium no energy as heat can be transferred between them?

a.	the zeroth law	c.	the second law
b.	the first law	d.	the third law

18. For a thermodynamic process to be adiabatic there must be no exchange of

a.	work.	c.	internal energy.
b.	mass.	d.	thermal energy.

19. An adiabatic process must happen

a.	at a very low temperature.	c.	very quickly.
b.	at a very high temperature.	d.	very slowly.

20. When you blow up a balloon

a.	your breath gains internal energy because it is doing work.	c.	your breath gets cooler because it is doing work.
b.	your breath loses internal energy because it is doing work.	d.	our breath gets hotter because it is doing work.

21. The term ‘thermodynamics’ means

a.	movement of heat.	c.	movement of vacuums.
b.	heat of movement.	d.	vacuums in motion.

22. According to the second law of thermodynamics what is the direction of heat?

a.	Nothing, heat has no direction	c.	from cold to hot
b.	Heat always goes up	d.	from hot to cold

23. According to the second law of thermodynamics entropy

a.	is always conserved	c.	always increases
b.	always decreases	d.	disappears

24. When we say that a substance is at absolute zero we are saying that

a.	no more energy can be added to it	c.	it ceases to exist.
b.	no more energy can be extracted from it.	d.	it becomes a black hole.

25. Water freezes at 0 ⁰C, this is the same as saying that water freezes at

a.	zero Kelvin	c.	273 Kelvin
b.	100 Kelvin	d.	373 Kelvin

26. A heat engine is a machine that allows high temperature energy to change to low temperature energy and in-between

a.	nothing happens.	c.	work is done
b.	energy is lost	d.	power is made

27. Whenever work is done

a.	wasted energy is produced.	c.	energy is stored.
b.	more useful energy is produced.	d.	energy is lost.

28. The bigger the difference between the hot place and the cold place of a heat engin ___

a.	the less efficient the machine.	c.	the less work the machine can do.
b.	the more efficient the machine.	d.	the more powerful the machine is.

29. It is a bad idea to cool your kitchen by opening the refrigerator door because

a.	it will cool the kitchen too fast.	c.	it will actually make the kitchen hotter.
b.	it will take a very long time for the kitchen to cool.	d.	it will bring the kitchen and the refrigerator into equilibrium.

30. Whenever work of any kind is done entropy

a.	decreases.	c.	inhibits the work from being done.
b.	increases.	d.	Makes the work easier to do.

CP Major Test Chapter 24: Thermodynamics

Answer Section

SHORT ANSWER

1. Considering the first law of thermodynamics:

a) As a law of conservation of energy the first law of thermodynamics states that energy cannot be created nor destroyed.

b) The 1st L of T in terms of adiabatic process states a change in air temperature is equivalent to a change in pressure. If the temperature of air increases so does its pressure; of the temperature of air decreases so does its pressure.

c) According to the first law of thermodynamics when a hot cup of coca cools the temperature in this classroom must get higher.

d) According to the first law of thermodynamics when the ice in a cup of ice water melts the temperature in this room must get lower.

2. Consider a heat engine pictured below. Note that the parts of the heat engine system are properly labeled.

3. Consider a refrigerator. A refrigerator removes energy as heat from its insides.

a) The refrigerator takes the energy as heat from its insides and dumps it into the kitchen.

b) A typical refrigerator might extract 1000 Joules of energy from its insides but by doing so it has to get rid of 1500 Joules of energy. The source of the additional 500 J is from the electricity the refrigerator uses when is compresses the refrigerant that cools the refrigerator as it expands again inside the refrigerator box.

c) It is a bad idea to cool your kitchen by leaving the refrigerator door open because it takes more work to cool the inside of the refrigerator than the energy it removes. In other words it takes 1500 J to remove 1000 J of energy as heat. This means that more energy will be needed to cool the room than the energy taken from it to make it cool. This, by opening the refrigerator door the kitchen will actually get warmer, not cooler.

TRUE/FALSE

4(A) 9(B) F

The study of thermodynamics is primarily concerned with macroscopic systems.

5(A) 13(B) F

According to the first law of thermodynamics whenever heat is added to a system, it transforms to an equal amount of some other form of energy.

6(A) 12(B) F

Adiabatic process must happen very quickly.

7(A) 10(B) T

8(A) 11(B) T

9(A) 7(B) F

As air rises it expands adiabatically and gets very cool; as air descends it contracts adiabatically and it gets warmer.

10(A) 4(B) T

11(A) 6(B) F

According to the second law of thermodynamics entropy must always increase when work is done.

12(A) 5(B) T

13(A) 8(B) F

A very good way to defining entropy is to define it in terms of the ability to do work; systems of low entropy can do more work then systems that have high entropy.

MULTIPLE CHOICE

ID A ID B

14. B B

15. A A

16. C B

17. A C

18. D A

19. C C

20. B D

21. A D

22. D B

23. C C

24. B A

25. C A

26. C C

27. A B

28. B B

29. C C

30. B C