Question 1

An engineer wants to use a river (minimum temperature of 4°C) to cool his electrical plant, which heats water with a boiler operating at 220°C. If he wishes to produce 185 kW of power using this plant, what is the minimum power he must supply to his boiler if it is maximally efficient?

Accepted Answer

A)  233 kW 
B)  187 kW 
C)  332 kW 
D)  422 kW

Question 2

A container of ideal gas at 0°C and 1 atm undergoes an isothermal expansion, and its entropy changes by 3.7 J/K. How much work does it do?

Accepted Answer

A)  zero 
B)  1.0 × 103 J 
C)  −1.0 × 103 J 
D)  None of these choices are correct.

Question 3

For an ideal gas undergoing an isothermal expansion, the work done on the gas is

Accepted Answer

A)  May be either, depending on the temperature 
B)  Positive 
C)  Zero 
D)  Negative

Question 4

10 joules of heat are transferred to a sample of ideal gas at constant pressure. As a result, the internal energy of the gas

Accepted Answer

A)  increases by 10 J 
B)  increases by less than 10 J 
C)  increases by more than 10 J 
D)  remains unchanged.

Question 5

An engineer uses a river (minimum temperature of 4°C) to cool his electrical plant, which heats water with a boiler operating at 220°C. His boiler uses 420 kW of energy to heat water to steam. What is the maximum power output under ideal circumstances?

Accepted Answer

A)  230 kW 
B)  184 kW 
C)  330 kW 
D)  416 kW

Question 6

An engineer uses a river (which averages 4°C) to cool his electrical plant, which heats water with a boiler operating at 750°C. What's the maximal performance (in terms of efficiency) theoretically possible for this electrical plant?

Accepted Answer

A)  64% 
B)  36% 
C)  27% 
D)  73%

Question 7

1.00 mol of oxygen gas (O2) is heated at constant pressure of 1.00 atm from 10.0°C to 25.0°C. What is the work done by the gas during this expansion?

Accepted Answer

A)  159 J 
B)  125 J 
C)  102 J 
D)  172 J

Question 8

A kilogram of water (c = 4.186 kJ/kg °C) is stirred using a 400−watt device for 5 minutes. At the end of this time the temperature of the water has increased by 15°C. How much heat was lost to the surroundings?

Accepted Answer

A)  90.1 kJ 
B)  57.2 kJ 
C)  82.6 kJ 
D)  38.9 kJ

Question 9

A refrigerator uses 40.0 J of work to extract heat from a heat reservoir at 0.00°C. If the coefficient of performance of the refrigerator is 2.10, then how much heat is discharged out of the refrigerator at a higher temperature?

Accepted Answer

A)  52.0 J 
B)  66.0 J 
C)  86.0 J 
D)  124 J

Question 10

A heat pump is used to heat a house in Minnesota in the winter and has half the ideal coefficient of performance for a reversible heat pump. If the outside air temperature is −15°C and the indoor temperature desired is 20°C, and if it inputs work at a rate of 1,250 W, what is the rate of heat flow into the house?

Accepted Answer

A)  5,230 W 
B)  1,100 W 
C)  625 W 
D)  300 W

Question 11

When an ideal gas is compressed isothermally

Accepted Answer

A)  the internal energy of the gas does not change. 
B)  the work done on the gas is zero. 
C)  heat flows into the gas. 
D)  the temperature of the gas increases.

Question 12

A refrigerator uses 40 J of work to extract heat from a heat reservoir at 0.00°C. If the coefficient of performance of the refrigerator is 2.1, then how much heat is extracted from the heat reservoir at 0.00°C?

Accepted Answer

A)  48 J 
B)  65 J 
C)  84 J 
D)  90 J

Question 13

A very efficient engine has the following characteristics-combustion = 1,900°C, exhaust = 430°C, 5.0 × 106 cal of fuel produces 1.4 × 107 J of work in one hour. What is the output in hp? (1 hp = 745.7 W)

Accepted Answer

A)  5.2 hp 
B)  8.1 hp 
C)  7.3 hp 
D)  6.3 hp

Question 14

For a system undergoing an isothermal process,

Accepted Answer

A)  Q = −ΔU 
B)  Q = 0 
C)  Q = ΔU 
D)  Q = −W 
E)  Q = W

Question 15

When 2.000 kg of water evaporates, 22.60 × 105 J/kg of heat are needed. What is the entropy change of the water in the boiling process?

Accepted Answer

A)  12,120 J/K 
B)  8,566 J/K 
C)  6,750 J/K 
D)  5,844 J/K

Question 16

10 joules of heat are transferred to a sample of ideal gas at constant volume. As a result, the internal energy of the gas

Accepted Answer

A)  increases by 10 J 
B)  increases by less than 10 J 
C)  increases by more than 10 J 
D)  remains unchanged.

Question 17

A engine goes through a cyclic process. During the cyclic process the engine takes in 3,200 J of heat and has a heat output of 2,400 J. What is the efficiency of the engine?

Accepted Answer

A)  10% 
B)  15% 
C)  25% 
D)  40% 
E)  52%

Question 18

A system performs 800 J of work while taking in 500 J of heat. What is the change in internal energy of the system?

Accepted Answer

A)  not possible. 
B)  300 J 
C)  −300 J 
D)  1,300 J 
E)  −1,300 J

Question 19

A heat pump is used to heat a house in Minnesota in the winter and has half the ideal coefficient of performance for a reversible heat pump. If the outside air temperature is −15°C and the indoor temperature desired is 20°C, what is its coefficient of performance under these conditions?

Accepted Answer

A)  3.7 
B)  1.1 
C)  2.0 
D)  4.2

Question 20

When water freezes, the entropy of the water

Accepted Answer

A)  increases. 
B)  decreases. 
C)  does not change. 
D)  depending on other factors could increase or decrease.

Exam 15: Thermodynamics