Homework 10

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14) A thermodynamic system undergoes a process in which its internal energy decreases by 500 J. If at the same time 220 J of work is done on the system, find the heat exchange between the system and the environment. Is this heat flowing into or out of the system?

 

 

17) A gas is enclosed in a container fitted with a piston of cross-sectional area 0.150 m2. The pressure of the gas is maintained at 6000 Pa as the piston moves inward 20.0 cm. (a) Calculate the work done by the gas. (b) if the internal energy of the gas decreases by 8.00 J, find the amount of heat removed from the system during the compression.

 

 

23) One gram of water changes to ice at a constant pressure of 1.00 atm and a constant temperature of 0oC. In the process, the volume changes from 1.00 cm3 to 1.09 cm3. (a) Find the work done on the water by the surroundings (that is, the work done by the pressure force of the air) and (b) the change in the internal energy of water. Lf (of water) = 3.33x105 j/kg

 

 

 

23) (7th Ed) A heat engine operates between two reservoirs at temperature of 20oC and 300oC. What is the maximum efficiency possible for this engine?

 

 

25) A 5.0-kg block of aluminum is heated from 20oC to 90oC at atmospheric pressure. Find (a) the work done by the aluminum against the force of air pressure of 1.013x105 Pa, and (b) the amount of heat energy transferred to it, and (c) the increase in its internal energy. The coefficient of linear expansion of Al is 24x10-6 /oC, its density at 20oC is 2.7x103 kg/m3 and its specific heat capacity c=900j/(kgoC).

 

 


37) An engine absorbs 1700j from a hot reservoir and expels 1200j to a cold reservoir in each cycle. (a) What is the engine's efficiency? (b) what is the work done by the engine, and (c) What is the power output of the engine if each cycle lasts 0.300 s?

 

 

47) A freezer is used to freeze 1.0 L of water initially at 0oC, completely into ice. The water and the freezer remain at a constant temperature of T = 0oC. Determine (a) the change in the entropy of the water and (b) the change in the entropy of the freezer.

 

 

 


48) What is the change in entropy of 1.00 kg of liquid water at 100 oC as it changes to steam at 100 oC? Lv (of water) = 2.26x106 j/kg

 

 


49) A 70-kg log falls from a height of 25 m into a lake. If the log, the lake, and the air are all at 300 K, find the change in entropy of the Universe at the end of this process.

 

In the details below we describe the notion of the Mechanical Equivalent of Heat: That Heat flow, like Work, is an energy transfer mechanism.

 

 

51) The surface of the Sun is approximately at 5700 K, and the temperature of the Earth's surface is approximately 290 K. What entropy change occurs when 1000 J of energy is transferred by heat from the Sun to the Earth?