Chapter 15: 15-7Q (page 412)
Would a definition of heat engine efficiency as \(e = \frac{W}{{{Q_{\rm{L}}}}}\) be useful? Explain.
The added heat energy \({Q_{\rm{H}}}\) is not present in the efficiency equation. Hence, this is not a useful definition of the efficiency of the heat engine.
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(II) A restaurant refrigerator has a coefficient of performance of 4.6. If the temperature in the kitchen outside the refrigerator is 32°C, what is the lowest temperature that could be obtained inside the refrigerator if it were ideal?
Question: (I) 1.0 kg of water is heated from 0°C to 100°C. Estimate the change in entropy of the water.
Question: Entropy is often called the‘time’s arrow’ because it tells us the direction in which natural processes occur. If a movie is run backward, name some processes that you might see that would tell you that time is ‘running backward’.
Question: (II) A heat pump is used to keep a house warm at 22°C. How much work is required of the pump to deliver 3100 J of heat into the house if the outdoor temperature is (a) 0°C, (b) \({\bf{ - 15^\circ C}}\)? Assume a COP of 3.0. (c) Redo for both temperatures, assuming an ideal (Carnot) coefficient of performance \({\bf{COP = }}{{\bf{T}}_{\bf{L}}}{\bf{/}}\left( {{{\bf{T}}_{\bf{H}}}{\bf{ - }}{{\bf{T}}_{\bf{L}}}} \right)\).
Can the temperature of a system remain constant even though heat flows into or out of it? If so, give examples.
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