Question 1

A cyclic process is carried out on an ideal gas such that it returns to its initial state at the end of a cycle, as shown in the pV diagram in the figure. If the process is carried out in a clockwise sense around the enclosed area, as shown on the figure, then the change of internal energy over the full cycle

Accepted Answer

A)  is positive. 
B)  is negative. 
C)  is zero. 
D)  cannot be determined from the information given.

Question 2

Oxygen condenses into a liquid at approximately 90 K. What temperature, in degrees Fahrenheit, does this correspond to?

Accepted Answer

A)  -193°F 
B)  -217°F 
C)  -265°F 
D)  -297°F

Question 3

Which of the following is a false statement?

Accepted Answer

A)  Entropy is a quantitative measure of disorder. 
B)  The total entropy change in one cycle of a Carnot engine is zero. 
C)  The entropy of an isolated system must be conserved (it remains constant). 
D)  Entropy can be measured in units of J/K.

Question 4

A refrigerator has a coefficient of performance equal to 4.2. How much work must be done on the operating gas in the refrigerator in order to remove 250 J of heat from the interior compartment?

Accepted Answer

A)  60 J 
B)  120 J 
C)  250 J 
D)  480 J 
E)  1050 J

Question 5

A refrigerator has a performance coefficient (COP) of 1.15, and it extracts 7.95 J of heat from the cold reservoir during each cycle.
(a) How much work is done on the gas in each cycle?
(b) How much heat is exhausted into the hot reservoir in each cycle?

Accepted Answer

The answer of A refrigerator has a performance coefficient (COP)...

Question 6

If the efficiency of a Carnot engine were to be 100%, the heat sink would have to be

Accepted Answer

A)  at absolute zero. 
B)  at 0°C. 
C)  at 100°C. 
D)  infinitely hot.

Question 7

During each cycle, a heat engine takes in 4.0 J of heat, does 1.0 J of work, and expels 3.0 J of heat. What is its efficiency?

Accepted Answer

The answer of During each cycle, a heat engine takes...

Question 8

A Carnot cycle consists of

Accepted Answer

A)  two adiabats and two isobars. 
B)  two isobars and two isotherms. 
C)  four isotherms. 
D)  two adiabats and two isotherms. 
E)  four adiabats.

Question 9

A sealed rigitd tank contains 30 moles of an ideal gas, at an initial temperature of $270 \mathrm {~K}$ The pressure of the gas is increased until the final pressure equals 1.40 times the initial pressure. The heat capacity at constant pressure of the gas is $32.0 \mathrm {~J} / \mathrm { mol } \cdot \mathrm { K }$ What is the change in the internal (thermal) energy of the gas during this process? (R = 8.31 J/mol ∙ K)

Accepted Answer

A)  77 kJ 
B)  100 kJ 
C)  130 kJ 
D)  -50 kJ 
E)  -23 kJ

Question 10

At room temperature, a typical person loses energy to the surroundings at the rate of 62 W. If this energy loss has to be made up by an equivalent food intake, how many kilocalories (food calories) does this person need to consume every day just to make up this heat loss? (1 cal = 4.186 J)

Accepted Answer

A)  1000 kcal 
B)  1100 kcal 
C)  1300 kcal 
D)  1500 kcal 
E)  1600 kcal

Question 11

During each cycle of operation, a refrigerator absorbs 230 J of heat from the freezer and expels 356 J of heat to the room. How much work input is required in each cycle?

Accepted Answer

A)  712 J 
B)  586 J 
C)  460 J 
D)  126 J

Question 12

During an isothermal process, 5.0 J of heat is removed from an ideal gas. What is the change in internal (thermal) energy of the gas?

Accepted Answer

A)  0 J 
B)  2.5 J 
C)  5.0 J 
D)  10 J

Question 13

The work done on an ideal gas system in an isothermal process is -400 J. What is the change in internal (thermal) energy of the gas?

Accepted Answer

A)  0 J 
B)  -400 J 
C)  400 J 
D)  200 J

Question 14

At what, if any, temperature are the numerical readings on the Fahrenheit and Celsius scales the same?

Accepted Answer

A)  -30° 
B)  -40° 
C)  -50° 
D)  -60° 
E)  They can never read the same because they are based on different zeroes.

Question 15

A reversible engine takes in heat at a rate of 555 W and exhausts heat at 482 W.
(a) How much power does it produce?
(b) What is its efficiency?
(c) If operated in reverse as a refrigerator, what would be its performance coefficient (COP)?

Accepted Answer

The answer of A reversible engine takes in heat at...

Question 16

A heat engine absorbs 64 kcal of heat each cycle and exhausts 42 kcal.
(a) What is the efficiency of this engine?
(b) How much work does this engine do per cycle?

Accepted Answer

The answer of A heat engine absorbs 64 kcal of...

Question 17

An ideal Carnot air conditioner operates between an indoor temperature of 20°C and an outdoor temperature of 39°C. How much energy does it use to remove 2000 J of heat from the interior of the house?

Accepted Answer

A)  105 J 
B)  130 J 
C)  780 J 
D)  520 J 
E)  340 J

Question 18

During an isochoric process, the internal (thermal) energy of a gas decreases by 50 J. How much heat is added to the gas during this process?

Accepted Answer

A)  0 J 
B)  50 J 
C)  -50 J 
D)  25 J 
E)  -25 J

Question 19

A heat engine having the maximum possible efficiency has an efficiency of 25% when operating between two heat reservoirs. If the temperature of the cold reservoir is 300 K, what is the temperature of the hot reservoir?

Accepted Answer

A)  350 K 
B)  375 K 
C)  400 K 
D)  450 K 
E)  500 K

Question 20

During each cycle, the compressor in a certain ideal Carnot refrigerator performs 480 J of work to remove 150 J of heat from the interior of the refrigerator. How much heat do the coils behind the refrigerator discharge into the kitchen each cycle?

Accepted Answer

A)  110 J 
B)  150 J 
C)  330 J 
D)  480 J 
E)  630 J

Exam 11: Using Energy