Exam 18: Heat Engines,entropy,and the Second Law of Thermodynamics

On a cold day,a heat pump absorbs heat from the outside air at 14 $\degree$ F (-10 $\degree$ C)and transfers it into a home at a temperature of 86 $\degree$ F (30 $\degree$ C).Determine the maximum COP of the heat pump.

A lawn mower has a 6-horsepower engine (1 HP = 750 W).If the engine has an efficiency of 20%,and the throttle is such that the engine cycles 10 times a second,the heat that is expelled in one cycle is

Selena states that $S _ { f } - S _ { i } = n R \ln \left( \frac { V _ { f } } { V _ { i } } \right)$ proves that entropy has a definite value at the beginning and end of an adiabatic free expansion.Ron says $S _ { f } - S _ { i } = k _ { B } \ln \left( \frac { W _ { f } } { W _ { i } } \right)$ ,where W is the number of microstates of a given macrostate.Which one,if either,is correct?

The reason that we can calculate the change in entropy of a system is that

Ten kilograms of water at 0 $\degree$ C is mixed with 10 kg of water at 100 $\degree$ C.The change in entropy (in cal/K)of the system is

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

When water of mass m and specific heat c is heated from absolute temperature T₁ to absolute temperature T₂,its change in entropy is

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

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

Which of the following is an almost reversible process?

Exactly 500 grams of ice are melted at a temperature of 32 $\degree$ F.(L_ice = 333 J/g. )The change in entropy (in J/K)is

In a nuclear power plant,the reactor produces 500 $\degree$ 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 $\degree$ 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 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?

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?

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?

Find the change in entropy (in J/K)when 5.00 moles of an ideal gas undergo a free expansion from an initial volume of 20 cm³ to a final volume of 100 cm³.

A gasoline engine absorbs 2 500 J of heat and performs 1 000 J of mechanical work in each cycle.The efficiency of the engine is

For the same temperature increase in a system,the change in entropy, $\Delta$ S,is largest in a reversible

An automobile engine operates with an overall efficiency of 12%.How much energy is delivered as waste heat (in gallons of gasoline)for each 10 gallons of fuel burned?

A violation of the second law of thermodynamics would occur if