23. The Second Law of Thermodynamics

A refrigerator has a coefficient of performance of 2.4. Each cycle, it takes in 3×10⁴ J of heat from the cold reservoir. How much is expelled to the hot reservoir?

A certain brand of freezer is advertised to use $730$ kWh of energy per year. What is the theoretical maximum amount of ice this freezer could make in an hour, starting with water at $20.0$°C?

A certain brand of freezer is advertised to use $730$ kWh of energy per year. Assuming the freezer operates for $5$ hours each day, how much power does it require while operating?

A refrigerator has a coefficient of performance of $2.25$, runs on an input of $135$ W of electrical power, and keeps its inside compartment at $5$°C. If you put a dozen $1.0$-L plastic bottles of water at $31$°C into this refrigerator, how long will it take for them to be cooled down to $5$°C? (Ignore any heat that leaves the plastic.)

The coefficient of performance $K=H/P$ is a dimensionless quantity. Its value is independent of the units used for $H$ and $P$, as long as the same units, such as watts, are used for both quantities. However, it is common practice to express $H$ in Btu/h and $P$ in watts. When these mixed units are used, the ratio $H/P$ is called the energy efficiency ratio ($EER$). If a room air conditioner has $K=3.0$, what is its $EER$?

Home air conditioners in the United States have their power specified in the truly obscure units of tons, where 1 ton is the power needed to melt 1 ton (2000 lb or 910 kg) of ice in 24 hours. A modest-size house typically has a 4.0 ton air conditioner. If a 4.0 ton air conditioner has a coefficient of performance of 2.5, a typical value, at what rate in kW is heat energy removed from the house?

100 mL of water at 15℃ is placed in the freezer compartment of a refrigerator with a coefficient of performance of 4.0. How much heat energy is exhausted into the room as the water is changed to ice at -15℃?

An air conditioner removes 5.0 x 10⁵ J/min of heat from a house and exhausts 8.0 x 10⁵ J/min to the hot outdoors. What is the air conditioner's coefficient of performance?

What are (a) the heat extracted from the cold reservoir and (b) the coefficient of performance for the refrigerator shown in FIGURE EX21.21?

A freezer with a coefficient of performance 30% that of a Carnot refrigerator keeps the inside temperature at -22℃ in a 25℃ room. 3.0 L of water at 20℃ are placed in the freezer. How long does it take for the water to freeze if the freezer's compressor does work at the rate of 200 W while the water is freezing?

An ideal (Carnot) engine has an efficiency of 33%. If it were possible to run it backward as a heat pump, what would be its coefficient of performance?

A “Carnot” refrigerator (the reverse of a Carnot engine) absorbs heat from the freezer compartment at a temperature of -17°C and exhausts it into the room at 25°C.

(a) How much work would the refrigerator do to change 0.65 kg of water at 25°C into ice at -17°C?

(b) If the compressor output is 105 W and runs 25% of the time, how long will this take?

If an ideal refrigerator keeps its contents at 2.5°C when the house temperature is 22°C, what is its COP?