Exam 11: Using Energy

Suppose that the Department of Energy develops a new reversible engine that has a coefficient of performance (COP) of 4.0 when operated as a refrigerator and a COP of 5.0 when operated as a heat pump. What is its thermal efficiency when operated as a heat engine doing work?

An ideal Carnot engine is operated as an air conditioner to cool a house in the summer. The air conditioner removes $14 \mathrm {~kJ}$ of heat per second from the house, and maintains the inside temperature at $293 \mathrm {~K}$ while the outside temperature is $369 \mathrm {~K}$ The power required to run the air conditioner under these operating conditions is closest to

A sealed rigid tank contains 29 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 1.90 times the initial pressure. The heat capacity at constant pressure of the gas is $24.0 \mathrm {~J} / \mathrm { mol } \cdot \mathrm { K }$ How much heat is absorbed by the gas during this process? (R = 8.31 J/mol ∙ K)

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

What is the efficiency of an ideal Carnot engine operating between a reservoir in which ice and water coexist, and a reservoir in which water and steam coexist? The pressure is constant at 1.0 atm for both reservoirs.

If the efficiency of a reversible engine is 28%, what is its COP (performance coefficient) operated (a) as a refrigerator, and (b) as a heat pump?

An ideal Carnot engine operates between a warm reservoir at 233 K and a colder reservoir. During each cycle, this engine extracts $15.0 \mathrm {~J}$ of heat from the warm reservoir and does $4.0 \mathrm {~J}$ of work. What is the temperature of the colder reservoir?

The second law of thermodynamics leads us to conclude that

An ideal gas undergoes an adiabatic process while doing 25 J of work. What is the change in the internal (thermal) energy of the gas?

The temperature changes from 35°F during the night to 75°F during the day. What is the temperature change on the Celsius scale?

A heat engine has an efficiency of 35.0% and receives 150 J of heat per cycle. (a) How much work does it do in each cycle? (b) How much heat does it "waste" in each cycle?

Express a body temperature 98.6°F in Celsius degrees.

During an isothermal process, 5.0 J of heat is removed from an ideal gas. What is the work done by the gas in the process?

The figure shows a pV diagram for a cycle of a heat engine for which Q_H = 59 J. What is the thermal efficiency of the engine?

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 magnitude of the enclosed area represents

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 counter-clockwise sense around the enclosed area, as shown on the figure, then the magnitude of the enclosed area represents

An ideal Carnot heat engine has an efficiency of 0.600. If it operates between a deep lake with a constant temperature of $294.0 \mathrm {~K}$ and a hot reservoir, what is the temperature of the hot reservoir?

An ideal Carnot engine has an efficiency of 83.0% and performs 4500 J of work every cycle. How much energy is discharged to the lower temperature reservoir every cycle?

Nitrogen boils at -196°C. What is the corresponding temperature in the Fahrenheit scale?

In an isochoric process, the internal (thermal) energy of a gas decreases by 50 J. How much work is done by the gas during this process?