Question 1

One of the most efficient engines built so far has the following characteristics: combustion chamber temperature = 1900°C, exhaust temperature = 430°C, 7.0 × 10⁹ cal of fuel produces 1.4 × 10¹⁰ J of work in one hour. (a) What is the actual efficiency of this engine? (b) What is the Carnot efficiency of the engine? (c) What is the power output, in hp, of this engine?

Accepted Answer

The answer of One of the most efficient engines built...

Question 2

The compressor in a certain Carnot refrigerator performs 480 J of work to remove 150 J of heat from the interior of the refrigerator. How much heat must the coils behind the refrigerator discharge into the kitchen?

Accepted Answer

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

Question 3

What is the change in entropy when 15.0 g of water at 100°C are turned into steam at 100°C? The latent heat of vaporization of water is 22.6 × 105 J/kg.

Accepted Answer

A)  90.8 J/K 
B)  -90.8 J/K 
C)  339 J/K 
D)  -339 J/K 
E)  0 J/K

Question 4

From the following statements regarding the ratio of the molar specific heat at constant pressure to the molar specific heat at constant volume, Cp/Cv, the only correct one for an ideal monatomic gas is

Accepted Answer

A)   = 1. 
B)   > 1. 
C)   p/Cv is sometimes more than 1, sometimes less than 1, but never equal to 1. 
E)  Cp/Cv is sometimes more than 1, sometimes equal to 1, but never less than 1.

Question 5

How much heat is required to increase the temperature of 1.70 moles of an ideal monatomic gas by 23.0 K at constant pressure?

Accepted Answer

A)  812 J 
B)  346 J 
C)  751 J 
D)  391 J 
E)  290 J

Question 6

On a hot day, you open the refrigerator and experience a refreshing feeling when the cool air comes in contact with your body. You think to yourself "I think that I'll just keep the refrigerator door open and stand in front of the refrigerator all day today to stay cool. I might even bring a chair." Will this work?
 Explain why or why not.

Accepted Answer

The answer of On a hot day, you open the...

Question 7

A heat engine with an efficiency of 30.0% performs 2500 J of work. How much heat is discharged to the lower temperature reservoir?

Accepted Answer

A)  5830 J 
B)  8330 J 
C)  750 J 
D)  1350 J 
E)  7080 J

Question 8

A 40.0-L container is divided into two equal parts by a rubber membrane. One half of the container has 1.50 moles of an ideal monatomic gas at 250 K, and the other half is a vacuum. The container is well insulated, so there is no exchange of heat with the surroundings. The membrane breaks, and eventually the gas reaches a new equilibrium condition occupying the entire volume. What is the final temperature of the gas?

Accepted Answer

A)  100 K 
B)  125 K 
C)  157 K 
D)  180 K 
E)  250 K

Question 9

A heat engine operating at maximum efficiency has an efficiency of 25%. 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 10

The pressure falls more rapidly in a quasi-static, adiabatic process than along an isotherm when the volume of the gas is increased.

Accepted Answer

A) True 
 B)False

Question 11

A certain gas is compressed adiabatically. The amount of work done on the gas is 800 J. What is the change in the internal energy of the gas?

Accepted Answer

A)  800 J 
B)  -800 J 
C)  400 J 
D)  0 J 
E)  More information is needed to answer this question.

Question 12

For water at 2°C,

Accepted Answer

A)  Cp = Cv. 
B)  Cp > Cv. 
C)  Cp v. 
D)  More information is needed to answer this question.

Question 13

20.0 L of a monatomic ideal gas at a pressure of 100 kPa expand adiabatically until the volume doubles. What is the pressure in the gas at that point?

Accepted Answer

A)  31.5 kPa 
B)  50.0 kPa 
C)  200 kPa 
D)  317 kPa 
E)  400 kPa

Question 14

What is the change in entropy when 50. g of ice melt at 0°C?

Accepted Answer

The answer of What is the change in entropy when...

Question 15

Which has the larger entropy:
 a gas that occupies only half of a container, with the other half a vacuum, or the same gas occupying the entire container?

Accepted Answer

The answer of Which has the larger entropy:
 a gas...

Question 16

All reversible engines operating between the same two temperatures have the same efficiency.

Accepted Answer

A) True 
 B)False

Question 17

A gas expands at constant temperature from an initial volume of 0.040 m3 and an initial pressure of 210 kPa until its pressure drops to 135 kPa. How much work is done by the system?

Accepted Answer

A)  3.0 kJ 
B)  3.7 kJ 
C)  4.1 kJ 
D)  5.6 kJ 
E)  7.9 kJ

Question 18

A Diesel engine uses adiabatic heating to ignite the fuel.

Accepted Answer

A) True 
 B)False

Question 19

A monatomic ideal gas is compressed isothermically to one-third of its initial volume. The resulting pressure will be

Accepted Answer

A)  three times as large as the initial value. 
B)  less than three times as large as the initial value. 
C)  more than three times as large as the initial value. 
D)  equal to the initial value. 
E)  impossible to predict on the basis of this data.

Question 20

2.50 moles of a monatomic ideal gas expand adiabatically from an initial temperature of 300 K and an initial volume of 80.0 L to a final volume of 150 L. What is the final temperature of the gas?

Accepted Answer

A)  840 K 
B)  563 K 
C)  426 K 
D)  287 K 
E)  197 K

Exam 18: The Laws of Thermodynamics

The compressor in a certain Carnot refrigerator performs 480 J of work to remove 150 J of heat from the interior of the refrigerator. How much heat must the coils behind the refrigerator discharge into the kitchen?

What is the change in entropy when 15.0 g of water at 100°C are turned into steam at 100°C? The latent heat of vaporization of water is 22.6 × 10⁵ J/kg.

From the following statements regarding the ratio of the molar specific heat at constant pressure to the molar specific heat at constant volume, C_p/C_v, the only correct one for an ideal monatomic gas is

How much heat is required to increase the temperature of 1.70 moles of an ideal monatomic gas by 23.0 K at constant pressure?

A heat engine with an efficiency of 30.0% performs 2500 J of work. How much heat is discharged to the lower temperature reservoir?

A heat engine operating at maximum efficiency has an efficiency of 25%. The temperature of the cold reservoir is 300 K. What is the temperature of the hot reservoir?

The pressure falls more rapidly in a quasi-static, adiabatic process than along an isotherm when the volume of the gas is increased.

A certain gas is compressed adiabatically. The amount of work done on the gas is 800 J. What is the change in the internal energy of the gas?

For water at 2°C,

20.0 L of a monatomic ideal gas at a pressure of 100 kPa expand adiabatically until the volume doubles. What is the pressure in the gas at that point?

What is the change in entropy when 50. g of ice melt at 0°C?

Which has the larger entropy: a gas that occupies only half of a container, with the other half a vacuum, or the same gas occupying the entire container?

All reversible engines operating between the same two temperatures have the same efficiency.

A gas expands at constant temperature from an initial volume of 0.040 m³ and an initial pressure of 210 kPa until its pressure drops to 135 kPa. How much work is done by the system?

A Diesel engine uses adiabatic heating to ignite the fuel.

A monatomic ideal gas is compressed isothermically to one-third of its initial volume. The resulting pressure will be

2.50 moles of a monatomic ideal gas expand adiabatically from an initial temperature of 300 K and an initial volume of 80.0 L to a final volume of 150 L. What is the final temperature of the gas?