Exam 22: Heat Engines, entropy, and the Second Law of Thermodynamics

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?

What is the probability of rolling either a 7 or 11 on a single roll of a pair of dice?

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

A gasoline engine absorbs 2 500 J of heat at 250°C and expels 2 000 J at a temperature of 50°C.The magnitude of the change in entropy (in J/K)for the system is

One kilogram of chilled water (0°C)is placed in a freezer which is kept at 0°F (−18°C).Approximately how much electric energy (in kilocalories)is needed just to freeze the water if the room temperature is maintained at 75°F (24°C)? (L_ice = 333 J/g;c_ice = 209 J/g⋅°C. )

An ideal heat engine can have an efficiency of 1 if the temperature of the low temperature reservoir is

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?

By operating a reversible heat engine with an ideal gas as the working substance in a Carnot cycle and measuring the ratio Q_c/Q_h,we can calculate

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?

For a pair of dice,how many microstates are there that result in the macrostate of rolling a 7?

In a nuclear power plant,the reactor produces 500°C steam that is used to power the steam turbines which generate 1 500 MW of electrical power.The cooling tower eliminates the waste heat at 50°C.If the efficiency of the plant were that of a Carnot engine,at what rate would waste heat be vented to the atmosphere?

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

Find the change in entropy (in J/K)when 5.00 moles of an ideal monatomic gas are allowed to expand isobarically from an initial volume of 20 cm³ to a final volume of 100 cm³.

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

Which answer below is not a statement of the second law of thermodynamics?

One kilogram of chilled water at 32°F (0°C)is placed in a freezer which is kept at 0°F (−18°C).Approximately how much electric energy (in kilocalories)is needed to operate the compressor to cool this water to 0°F if the room temperature is maintained at 75°F (24°C)? (L_ice = 3.33 × 10⁵ J/kg;c_ice = 2.09 × 10³ J/kg⋅°C)

The change in entropy of a mass m of a solid substance which has a latent heat of fusion L and melts at a temperature T is

A violation of the second law of thermodynamics would occur if

100 grams of molten lead (600°C)is used to make musket balls.If the lead shot is allowed to cool to room temperature (21°C),what is the change in entropy (in J/K)of the lead? (For the specific heat of molten and solid lead use 1.29 J/g⋅°C;the latent heat of fusion and the melting point of lead are 2.45 × 10⁴ J/kg and 327°C. )

A homeowner has a new oil furnace which has an efficiency of 60%.For every 100 barrels of oil needed to heat his house,how much (in barrels of oil)goes up the chimney as waste heat?