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Exam 16: Thermodynamics

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Question 31

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A closed 2.0-L container holds 3.0 mol of an ideal gas. If 150 J of heat is added, what is the change in internal energy of the system?

A) zero
B) 100 J
C) 150 J
D) 200 J

E) All of the above
F) None of the above

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Question 32

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You have a P-V diagram for a device going through a cyclic process forming a closed loop on the diagram. How can you tell from the diagram whether the device is acting as a heat engine and not as a refrigerator?

A) The loop is longer than it is high which means it is acting as a refrigerator.
B) The loop is higher than it is long which means it is acting as a refrigerator.
C) The loop proceeds clockwise which means it is acting as a heat engine.
D) The loop proceeds counterclockwise which means it is acting as a heat engine.

E) C) and D)
F) A) and C)

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Question 33

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A Carnot engine runs between a hot reservoir at T_h and a cold reservoir at T_c. If one of the temperatures is either increased or decreased by 3.5 K, which of the following changes would increase the efficiency by the greatest amount?

A 2.0-mol ideal gas system is maintained at a constant volume of 4.0 L. If 200 J of heat is added, what is the work done on the system?

An electrical power plant manages to send 88% of the heat produced in the burning of fossil fuel into the water-to-steam conversion. Of the heat carried by the steam, 30% is converted to the mechanical energy of the spinning turbine. Which of the following choices best describes the overall efficiency of the heat-to-work conversion in the plant (as a percentage) ?

An adiabatic expansion refers to the fact that:

When gasoline is burned, it gives off 46,000 J/g of heat energy. If an automobile uses 13.0 kg of gasoline per hour with an efficiency of 18%, what is the average horsepower output of the engine? (1 hp = 746 W)

A heat engine receives 6000 J of heat from its combustion process and loses 3600 J through the exhaust and friction. What is its efficiency?

According to the first law of thermodynamics, the sum of the heat gained by a system and the work done on that same system is equivalent to which of the following?

The laws of thermodynamics can be related to the following: (i) the measurement of temperature, (ii) the lowest temperature possible, (iii) conservation of energy, and (iv) only part of heat energy available may be turned into work. Which of these involve the first and second law?

If a heat engine has an efficiency of 30% and its power output is 600 W, what is the rate of heat input from the combustion phase?

A thermodynamic process that happens very quickly tends to be:

In an isovolumetric process by an ideal gas, the system's heat gain is equivalent to its change in:

A system has an increase in internal energy of 60 J while 90 J was removed from the system by heat. How much work was involved during this process and was it done on the system or done on its environment?

During each cycle of operation a refrigerator absorbs 45 cal from the freezer compartment and expels 85 cal to the room. If one cycle occurs every 8.0 s, how many minutes will it take to freeze 500 g of water, initially at 0 $\degree$ C? (L_v = 80 cal/g)

If one could observe the individual atoms making up a piece of matter and note that during a process of change their motion somehow became more orderly, then one may assume which of the following in regard to the system?

Three Carnot engines operate between temperature reservoirs as follows: Engine A: T_h = 1300 K, T_c = 1000 K; Engine B: T_h = 1000 K, T_c = 700 K; Engine C: T_h = 500 K, T_c = 350 K. Which two engines have the same thermal efficiency?

The P-V diagram of a cyclic process shows a curve that encloses an area. The work done by the heat engine, represented by the enclosed area, is positive when the path around the area proceeds in which of the following fashions?

An avalanche of ice and snow of mass 2500 kg slides a vertical distance of 160 m down a mountainside. If the temperature of the ice, snow, mountain, and surrounding air are all at 0 $\degree$ C, what is the change in entropy of the universe?

Two kilograms of water at 1.00 atm at the boiling point of 100 $\degree$ C is heated until all the water vaporizes. What is its change in entropy? (For water, L_v = 2.26 * 10⁶ J/kg)