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Question
Hello,

I spent hours on this problem to no avail. I know I'm supposed to use k = heat removed / net work input = Qc / Wnet  and since the water is initially at 0 C , Qc = mL is the amount of heat that must be removed. i have no idea how to proceed and all attempts gave me the wrong answer. Any help is tremendously appreciated.

a reversible refrigerator has a coefficient of performance of 2.60 . how much work must be done to freeze 1.40 kg of liquid water initially at 0 C? in kj

Answer
Hello sarah,

The amount of heat to be removed from the water is given by
Qc = m*L = 1.40kg*334 kJ/kg = 467.6 kJ

k = heat removed / net work input
2.60 = 467.6 kJ / net work input

net work input = 467.6 kJ / 2.60 = 180 kJ

I hope this helps,
Steve

Physics

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Steve Johnson

Expertise

I would be delighted to help with questions up through the first year of college Physics. Particularly Electricity, Electronics and Newtonian Mechanics (motion, acceleration etc.). I decline questions on relativity and Atomic Physics. I also could discuss the Space Shuttle and space flight in general.

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I have a BS in Physics and an MS in Electrical Engineering. I am retired now. My professional career was in Electrical Engineering with considerable time spent working with accelerometers, gyroscopes and flight dynamics (Physics related topics) while working on the Space Shuttle. I gave formal classroom lessons to technical co-workers periodically over a several year period.

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BS Physics, North Dakota State University
MS Electrical Engineering, North Dakota State University

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