Chapter 15: The Laws of Thermodynamics

Question: (I) The low temperature of a freezer cooling coil is\({\bf{ - 8^\circ C}}\)and the discharge temperature is\({\bf{33^\circ C}}\). What is the maximum theoretical coefficient of performance?

Question: (II) What is the temperature inside an ideal refrigerator-freezer that operates with a COP = 7.0 in a 22°C room?

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 \({\bf{COP = }}{{\bf{T}}_{\bf{L}}}{\bf{/}}\left( {{{\bf{T}}_{\bf{H}}}{\bf{ - }}{{\bf{T}}_{\bf{L}}}} \right)\).

Question: (II) (a) What is the coefficient of performance of an ideal heat pump that extracts heat from 6°C air outside and deposits heat inside a house at 24°C? (b) If this heat pump operates on 1200 W of electrical power, what is the maximum heat it can deliver into the house each hour? See Problem 35.

Question: (II) What volume of water at 0°C can a freezer make into ice cubes in 1.0 h, if the coefficient of performance of the cooling unit is 6.0 and the power input is 1.2 kilowatt?

Question: (II) How much less per year would it cost a family to operate a heat pump that has a coefficient of performance of 2.9 than an electric heater that costs \(2000 to heat their home for a year? If the conversion to the heat pump costs \)15,000, how long would it take the family to break even on heating costs? How much would the family save in 20 years?

Question: (I) What is the change in entropy of 320 g of steam at 100°C when it is condensed to water at 100°C?

(II) Sketch a PV diagram of the following process: 2.5 L of ideal gas at atmospheric pressure is cooled at constant pressure to a volume of 1.0 L, and then expanded isothermally back to 2.5 L, whereupon the pressure is increased at constant volume until the original pressure is reached.

Question: (I) 1.0 kg of water is heated from 0°C to 100°C. Estimate the change in entropy of the water.

What is the change in entropy of\({\bf{1}}{\bf{.00}}\;{{\bf{m}}{\bf{3}}}\)water at 0°C when it is frozen to ice at 0°C?