8. According to the second law of thermodynamics, for any process that may occur within an isolated system, which one of the choices applies? A) Entropy remains constant. B) Entropy increases. C) Entropy decreases. D) Both Alnd B are possible. E) Both A and C are possible, Answer Explanation.

8. According to the second law of thermodynamics, for any process that may occur within an isolated system, which one of the choices applies? A) Entropy remains constant. B) Entropy increases. C) Entropy decreases. D) Both Alnd B are possible. E) Both A and C are possible, Answer Explanation.

Physics for Scientists and Engineers: Foundations and Connections

1st Edition

ISBN:9781133939146

Author:Katz, Debora M.

Publisher:Katz, Debora M.

Chapter21: Heat And The First Law Of Thermodynamics

Section: Chapter Questions

Problem 34PQ: A thermodynamic cycle is shown in Figure P21.34 for a gas in a piston. The system changes states...

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(a) On a winter day, a certain house loses 5.00108J of heat to the outside (about 500,000 Btu). What is the total change in entropy due to this heat transfer alone, assuming an average indoor temperature of 21.0C and an average outdoor temperature of 5.00C ? (b) This large change in entropy implies a large amount of energy has become unavailable to do work. Where do we find more energy when such energy is lost to us?
(a) In reaching equilibrium, how much heat transfer occurs from 1.00 kg of water at 40.0C when it is placed in contact with 1.00 kg of 20.0C water in reaching equilibrium? (b) What is the change in entropy due to this heat transfer? (c) How much work is made unavailable, taking the lowest temperature to be 20.0C ? Explicitly show how you follow the steps in the Problem-Solving Strategies for Entropy.
(a) How much heat transfer occurs to the environment by an electrical power station that uses 1.251014J of heat transfer into the engine with an efficiency of 42.0%? (b) What is the ratio of heat transfer to the environment to work output? (c) How much work is done?
(a) How much heat transfer occurs from 20.0 kg of 90.0C water placed in contact with 20.0 kg of 10.0C water, producing a final temperature of 50.0C ? (b) How much work could a Carnot engine do with this heat transfer, assuming it operates between two reservoirs at constant temperatures of 90.0C and 10.0C ? (c) What increase in entropy is produced by mixing 20.0 kg of 90.0C water with 20.0 kg of 10.0C water? (d) Calculate the amount of work made unavailable by this mixing using a low temperature of 10.0C, and compare it with the work done by the Garnet engine. Explicitly show how you follow the steps in the Problem-Solving Strategies for Entropy. (e) Discuss how everyday processes make increasingly more energy unavailable to do work, as implied by this problem.
An ideal gas is compressed to half its initial volume by means of several possible processes. Which of the following processes results in the most work done on the gas? (a) isothermal (b) adiabatic (c) isobaric (d) The work done is independent of the process.
A sample of a monatomic ideal gas is contained in a cylinder with a piston. Its stale is represented by the dot in the PV diagram shown in Figure OQ22.9. Arrows A through E represent isobaric, isothermal, adiabatic, and isovolumetric processes that the sample can undergo. In each process except D, the volume changes by a factor of 2. All five processes are reversible. Rank the processes according to the change in entropy of the gas from the largest positive value to the largest-magnitude negative value. In your rankings, display any cases of equality.
Assume a sample of an ideal gas is at room temperature. What action will necessarily make the entropy of the sample increase? (a) Transfer energy into it by heat, (b) Transfer energy into it irreversibly by heat, (c) Do work on it. (d) Increase either its temperature or its volume, without letting the other variable decrease, (e) None of those choices is correct.
A power plant has been proposed that would make use of the temperature gradient in the ocean. The system is to operate between 20.0C (surface water temperature) and 5.00C (water temperature at a depth of about 1 km). (a) What is the maximum efficiency of such a system? (b) If the useful power output of the plant is 75.0 MW, how much energy is absorbed per hour? (c) In view of your answer to part (a), do you think such a system is worthwhile (considering that there is no charge for fuel)?
(a) What is the best coefficient of performance for a heat pump that has a hot reservoir temperature of 50.0C and a cold reservoir temperature of 20.0C ? (b) How much heat transfer occurs into the warm environment if 3.60107J of work (10.0kWh) is put into it? (c) If the cost of this work input is 10.0cent/kWh, haw does its cost compare with the direct heat transfer achieved by burning natural gas at a cost of 85.0 cents per therm. (A therm is a common unit of energy for natural gas and equals 1.055108J .)
A thermodynamic cycle is shown in Figure P21.34 for a gas in a piston. The system changes states along the path ABCA. a. What is the total work done by the gas during this cycle? b. How much heat is transferred? Does heat flow into or out of the system? Figure P21.34
(a) What is the best coefficient of performance for a refrigerator that cools an environment at 30.0C and has heat transfer to another environment at 45.0C ? (b) How much work in joules must be done for a heat transfer of 4186 kJ from the cold environment? (c) What is the cost of doing this if the work costs 10.0 cents per 3.60106J (a kilowatthour)? (d) How many kJ of heat transfer occurs into the warm environment? (e) Discuss what type of refrigerator might operate between these temperatures.
Suppose an ideal (Carnot) heat pump could be constructed for use as an air conditioner. (a) Obtain an expression for the coefficient of performance (COP) for such an air conditioner in terms of Tb and Tc. (b) Would such an air conditioner operate on a smaller energy input if the difference in the operating temperatures were greater or smaller? (c) Compute the COP for such an air conditioner if the indoor temperature is 20.0C and the outdoor temperature is 40.0C.