Exam 22: Entropy and the Second Law of Thermodynamics

A heat engine absorbs 2500 J of heat from a hot reservoir and expels 1000 J to a cold reservoir. When it is run in reverse, with the same reservoirs, the engine pumps 2500 J of heat to the hot reservoir, requiring 1500 J of work to do so. Find the ratio of the work done by the heat engine to the work done by the pump. Is the heat engine reversible?

An ideal gas is allowed to undergo a free expansion. If its initial volume is V1 and its final volume is V2, the change in entropy is

An engine is designed to obtain energy from the temperature gradient of the ocean. What is the thermodynamic efficiency of such an engine if the temperature of the surface of the water is 59°F (15°C) and the temperature well below the surface is 41°F (5°C)?

Since LF,ice = 333 J/g, what is the change in entropy (in cal/K) when 1.00 kg of ice melts?

One end of a copper rod is in thermal contact with a hot reservoir at T = 500 K and the other end is in thermal contact with a cooler reservoir at T = 300 K. Find the entropy change of each reservoir, and the total entropy change, when 8000 J of heat energy are conducted from one end of the rod to the other with no change in the temperature distribution in the rod.

A violation of the second law of thermodynamics would occur if

All real engines are less efficient than the Carnot engine because

A steam engine is operating at its theoretical maximum efficiency of 60%. If the waste heat has a temperature of 100°F (38°C), what is the temperature of the boiler?

A 4.00-liter container is divided into two equal parts, one part containing 0.0100 mole of neon, and the other part containing 0.0100 mole of helium. The divider is removed and the gases mix. What is the change in entropy (in J/K) of this system?

For the same temperature increase in a system, the change in entropy, ΔS, is largest in a reversible

A gasoline engine absorbs 2500 J of heat and performs 1000 J of mechanical work in each cycle. The efficiency of the engine is

An ideal gas is allowed to expand adiabatically. Assume the process is reversible. What is the change in entropy?

A refrigerator has a coefficient of performance of 4. If the refrigerator absorbs 30 cal of heat from the cold reservoir in each cycle, the heat expelled (in cal) into the heat reservoir is

What is the change in entropy when 1 kg of ice melts at 0°C is (in J/K)? (LF,ice = 333 J/g.)

Suppose there are 3 molecules in a container. If each molecule has a 1-in-2 chance of being in the left half of the container, what is the probability that there are exactly 2 molecules in the left half of the container?

The thermal efficiency of a heat engine is given by

A heat pump has a coefficient of performance of 4. If the heat pump absorbs 20 cal of heat from the cold outdoors in each cycle, the heat expelled (in cal) to the warm indoors is

A vessel containing 5.0 kg of water at 10°C is put into a refrigerator. The 1/7 HP motor (1 HP = 746 W) runs for 5.0 minutes to cool the liquid to the refrigerator's low temperature, 0°C. What is the COP of the refrigerator?

A company that produces pulsed gas heaters claims their efficiency is approximately 90%. If an engine operates between 250°C and 25°C, what is its maximum thermodynamic efficiency?

A new electric power plant has an efficiency of 42%. For every 100 barrels of oil needed to run the turbine, how many are essentially lost as waste heat (in barrels of oil) to the environment?