Exam 19: The Second Law of Thermodynamics

If a steam engine operates at half of its theoretical maximum efficiency (e_max)and does work at a rate of W J/s,calculate how much heat is discharged per second.

An engine operating in a cycle would violate the second law of thermodynamics if it

A heat engine absorbs 150 J of heat from a hot reservoir and rejects 90 J to a cold reservoir.What is the efficiency of this engine?

A Carnot engine operating between reservoir temperatures of 340º C and 40ºC has an efficiency of

A refrigerator extracts heat Q from a cold reservoir.The heat exhausted to a hot reservoir

A Carnot heat engine absorbs heat Q from a hot reservoir at 127ºC and exhausts heat to a cold reservoir at 27ºC.How much heat is exhausted to the cold reservoir?

Of the four steps in the Carnot cycle,

A heat engine absorbs 70 kcal of heat from a hot reservoir and exhausts 50 kcal to a cold reservoir each cycle.Its efficiency is

A refrigerator extracts 25 kJ from a cold reservoir and rejects 35 kJ to a hot reservoir.What is the coefficient of performance of this refrigerator?

You want to construct a perfect refrigerator from a perfect heat engine.What else do you need?

The change in the entropy of the universe due to an operating Carnot engine

A steam engine operates between a high and low temperature of 550 ^$\circ$ C and 180 ^$\circ$ C.If the steam engine operates at 40% of its theoretical maximum efficiency and does work at a rate of 1000 W,calculate how much heat is discharged per hour.

Two moles of a gas at T = 350 K expand quasistatically and isothermally from an initial volume of 20 L to a final volume of 60 L.The change in entropy of the gas during this expansion is (R = 8.314 J/mol·K)

Use the following diagram to answer the next problem. An ideal heat engine uses 0.01 mol of gas and operates between a hot reservoir at T_H = 400 K and cold reservoir at T_L = 300 K, in a cycle from a→b→c→d→a. From a→b the gas undergoes an isothermal expansion, changing its volume from Va to 2.5Va. From b→c, the pressure is reduced at a constant volume. From c→d, the gas undergoes an isothermal compression, and from d→a, the pressure is increased at a constant volume until the gas is back at the original condition at a. -How much heat is absorbed in going from a $\to$ b?

Which of the following statements is true of an isolated system consisting of 15 gas molecules?

Entropy is related to probability.An isolated system moves toward

The Carnot cycle consists of

Three moles of a gas at T = 250 K expand quasi-statically and adiabatically from an initial volume of 30 L to a final volume of 60 L.The change in entropy of the gas during this expansion is (R = 8.314 J/mol·K)

A heat engine exhausts heat Q to a cold reservoir.The amount of work done by the engine

The maximum theoretical thermal efficiency of a steam engine that is supplied steam at a temperature of 600ºC and exhausts it at a temperature of 200ºC is