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Test prep for ap courses

Equal masses of steam (100 degrees C) and ice (0 degrees C) are placed in contact with each other in an otherwise insulated container. They both end up as liquid water at a common temperature. The steam ___ entropy and ___ order, while the ice ___ entropy and ___ order.

  1. gained, gained, lost, lost
  2. gained, lost, lost, gained
  3. lost, gained, gained, lost
  4. lost, lost, gained, gained

(c)

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A high temperature reservoir losing heat and hence entropy is a reversible process. A low temperature reservoir gaining a certain amount of heat and hence entropy is a reversible process. But a high temperature reservoir losing heat to a low temperature reservoir is irreversible. Why?

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Section summary

  • Entropy is the loss of energy available to do work.
  • Another form of the second law of thermodynamics states that the total entropy of a system either increases or remains constant; it never decreases.
  • Entropy is zero in a reversible process; it increases in an irreversible process.
  • The ultimate fate of the universe is likely to be thermodynamic equilibrium, where the universal temperature is constant and no energy is available to do work.
  • Entropy is also associated with the tendency toward disorder in a closed system.

Conceptual questions

A woman shuts her summer cottage up in September and returns in June. No one has entered the cottage in the meantime. Explain what she is likely to find, in terms of the second law of thermodynamics.

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Consider a system with a certain energy content, from which we wish to extract as much work as possible. Should the system's entropy be high or low? Is this orderly or disorderly? Structured or uniform? Explain briefly.

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Does a gas become more orderly when it liquefies? Does its entropy change? If so, does the entropy increase or decrease? Explain your answer.

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Explain how water's entropy can decrease when it freezes without violating the second law of thermodynamics. Specifically, explain what happens to the entropy of its surroundings.

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Is a uniform-temperature gas more or less orderly than one with several different temperatures? Which is more structured? In which can heat transfer result in work done without heat transfer from another system?

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Give an example of a spontaneous process in which a system becomes less ordered and energy becomes less available to do work. What happens to the system's entropy in this process?

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What is the change in entropy in an adiabatic process? Does this imply that adiabatic processes are reversible? Can a process be precisely adiabatic for a macroscopic system?

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Does the entropy of a star increase or decrease as it radiates? Does the entropy of the space into which it radiates (which has a temperature of about 3 K) increase or decrease? What does this do to the entropy of the universe?

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Explain why a building made of bricks has smaller entropy than the same bricks in a disorganized pile. Do this by considering the number of ways that each could be formed (the number of microstates in each macrostate).

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Problem exercises

(a) On a winter day, a certain house loses 5 . 00 × 10 8 J size 12{5 "." "00"´"10" rSup { size 8{8} } " J"} {} 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 21.0º C size 12{"21" "." 0°C} {} and an average outdoor temperature of 5.00º C size 12{5 "." "00"°C} {} ? (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) 9.78 × 10 4 J/K size 12{9 "." "79" times "10" rSup { size 8{4} } " J/K"} {}

(b) In order to gain more energy, we must generate it from things within the house, like a heat pump, human bodies, and other appliances. As you know, we use a lot of energy to keep our houses warm in the winter because of the loss of heat to the outside.

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On a hot summer day, 4 . 00 × 10 6 J size 12{4 "." "00"´"10" rSup { size 8{6} } " J"} {} of heat transfer into a parked car takes place, increasing its temperature from 35.0º C size 12{"35" "." 0°C} {} to 45.0º C size 12{"45" "." 0°C} {} . What is the increase in entropy of the car due to this heat transfer alone?

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A hot rock ejected from a volcano's lava fountain cools from 1100º C size 12{"1100"°C} {} to 40.0º C size 12{"40" "." 0°C} {} , and its entropy decreases by 950 J/K. How much heat transfer occurs from the rock?

8.01 × 10 5 J size 12{8 "." "01" times "10" rSup { size 8{5} } " J"} {}

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When 1 . 60 × 10 5 J size 12{1 "." "60"´"10" rSup { size 8{5} } " J"} {} of heat transfer occurs into a meat pie initially at 20.0º C size 12{"20" "." 0°C} {} , its entropy increases by 480 J/K. What is its final temperature?

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The Sun radiates energy at the rate of 3 . 80 × 10 26 W size 12{3 "." "80"´"10" rSup { size 8{"26"} } " W"} {} from its 5500º C size 12{"5500"°C} {} surface into dark empty space (a negligible fraction radiates onto Earth and the other planets). The effective temperature of deep space is 270º C size 12{-"270"°C} {} . (a) What is the increase in entropy in one day due to this heat transfer? (b) How much work is made unavailable?

(a) 1 . 04 × 10 31 J/K size 12{1 "." "04" times "10" rSup { size 8{"31"} } " J/K"} {}

(b) 3 . 28 × 10 31 J size 12{3 "." "28" times "10" rSup { size 8{"31"} } " J"} {}

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(a) In reaching equilibrium, how much heat transfer occurs from 1.00 kg of water at 40.0º C size 12{"40" "." 0°C} {} when it is placed in contact with 1.00 kg of 20.0º C size 12{"20" "." 0°C} {} 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 20.0º C size 12{"20" "." 0°C} {} ? Explicitly show how you follow the steps in the Problem-Solving Strategies for Entropy .

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What is the decrease in entropy of 25.0 g of water that condenses on a bathroom mirror at a temperature of 35.0º C size 12{"35" "." 0°C} {} , assuming no change in temperature and given the latent heat of vaporization to be 2450 kJ/kg?

199 J/K

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Find the increase in entropy of 1.00 kg of liquid nitrogen that starts at its boiling temperature, boils, and warms to 20.0º C size 12{"20" "." 0°C} {} at constant pressure.

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A large electrical power station generates 1000 MW of electricity with an efficiency of 35.0%. (a) Calculate the heat transfer to the power station, Q h size 12{Q rSub { size 8{h} } } {} , in one day. (b) How much heat transfer Q c size 12{Q rSub { size 8{c} } } {} occurs to the environment in one day? (c) If the heat transfer in the cooling towers is from 35.0º C size 12{"35" "." 0°C} {} water into the local air mass, which increases in temperature from 18.0º C size 12{"18" "." 0°C} {} to 20.0º C size 12{"20" "." 0°C} {} , what is the total increase in entropy due to this heat transfer? (d) How much energy becomes unavailable to do work because of this increase in entropy, assuming an 18.0º C size 12{"18" "." 0°C} {} lowest temperature? (Part of Q c size 12{Q rSub { size 8{c} } } {} could be utilized to operate heat engines or for simply heating the surroundings, but it rarely is.)

(a) 2 . 47 × 10 14 J size 12{2 "." "47" times "10" rSup { size 8{"14"} } " J"} {}

(b) 1 . 60 × 10 14 J size 12{1 "." "60" times "10" rSup { size 8{"14"} } " J"} {}

(c) 2.85 × 10 10 J/K size 12{2 "." "86" times "10" rSup { size 8{"10"} } " J/K"} {}

(d) 8.29 × 10 12 J size 12{8 "." "31" times "10" rSup { size 8{"12"} } " J"} {}

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(a) How much heat transfer occurs from 20.0 kg of 90.0º C size 12{"90" "." 0°C} {} water placed in contact with 20.0 kg of 10.0º C size 12{"10" "." 0°C} {} water, producing a final temperature of 50.0º C size 12{"50" "." 0°C} {} ? (b) How much work could a Carnot engine do with this heat transfer, assuming it operates between two reservoirs at constant temperatures of 90.0º C size 12{"90" "." 0°C} {} and 10.0º C size 12{"10" "." 0°C} {} ? (c) What increase in entropy is produced by mixing 20.0 kg of 90.0º C size 12{"90" "." 0°C} {} water with 20.0 kg of 10.0º C size 12{"10" "." 0°C} {} water? (d) Calculate the amount of work made unavailable by this mixing using a low temperature of 10.0º C size 12{"10" "." 0°C} {} , and compare it with the work done by the Carnot 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.

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Questions & Answers

If a prism is fully imersed in water then the ray of light will normally dispersed or their is any difference?
Anurag Reply
the same behavior thru the prism out or in water bud abbot
Ju
If this will experimented with a hollow(vaccum) prism in water then what will be result ?
Anurag
What was the previous far point of a patient who had laser correction that reduced the power of her eye by 7.00 D, producing a normal distant vision power of 50.0 D for her?
Jaydie Reply
What is the far point of a person whose eyes have a relaxed power of 50.5 D?
Jaydie
What is the far point of a person whose eyes have a relaxed power of 50.5 D?
Jaydie
A young woman with normal distant vision has a 10.0% ability to accommodate (that is, increase) the power of her eyes. What is the closest object she can see clearly?
Jaydie
29/20 ? maybes
Ju
In what ways does physics affect the society both positively or negatively
Princewill Reply
how can I read physics...am finding it difficult to understand...pls help
rerry Reply
try to read several books on phy don't just rely one. some authors explain better than other.
Ju
And don't forget to check out YouTube videos on the subject. Videos offer a different visual way to learn easier.
Ju
hope that helps
Ju
I have a exam on 12 february
David Reply
what is velocity
Jiti
the speed of something in a given direction.
Ju
what is a magnitude in physics
Jiti Reply
Propose a force standard different from the example of a stretched spring discussed in the text. Your standard must be capable of producing the same force repeatedly.
Giovani Reply
What is meant by dielectric charge?
It's Reply
what happens to the size of charge if the dielectric is changed?
Brhanu Reply
omega= omega not +alpha t derivation
Provakar Reply
u have to derivate it respected to time ...and as w is the angular velocity uu will relace it with "thita × time""
Abrar
do to be peaceful with any body
Brhanu Reply
the angle subtended at the center of sphere of radius r in steradian is equal to 4 pi how?
Saeed Reply
if for diatonic gas Cv =5R/2 then gamma is equal to 7/5 how?
Saeed
define variable velocity
Ali Reply
displacement in easy way.
Mubashir Reply
binding energy per nucleon
Poonam Reply
Practice Key Terms 3

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Source:  OpenStax, College physics for ap® courses. OpenStax CNX. Nov 04, 2016 Download for free at https://legacy.cnx.org/content/col11844/1.14
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