Second Law of Themodynamics

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Second Law Of Thermodynamics

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1. In a reversible process the system :A) is always close to equilibrium statesB) is close to equilibrium states only at the beginning and endC) might never be close to any equilibrium stateD) is close to equilibrium states throughout, except at the beginning and end

2. A slow (quasi-static) process is NOT reversible if :A) the temperature changes B) energy is absorbed or emitted as heatC) work is done on the system D) friction is present

3. The difference in entropy B AS S S for two states A and B of a system can computed

as the integral dQ / T provided :

A) A and B are on the same adiabatB) A and B have the same temperatureC) a reversible path is used for the integralD) the work done on the system is first computed

4. Which of the following is NOT a state variable ?A) Work B) Internal energy C) Entropy D) Temperature

5. The change in entropy is zero for :A) reversible adiabatic processesB) reversible isothermal processesC) reversible processes during which no work is doneD) reversible isobaric processes

6. Which of the following processes leads to a change in entropy of zero for the system under-going the process ?A) Non-cyclic isobaric (constant pressure ) B) Non-cyclic isochoric (constant volume)C) Non-cyclic isothermal (constant temperature) D) Any closed cycle

7. An ideal gas expands into a vacuum in a rigid vessel. As a result there is :A) a change in entropy B) an increase of pressureC) a change in temperature D) a decrease of internal energy

8. Consider all possible isothermal contractions of an ideal gas. The entropy of the gas :A) does not change for any of them B) decreases for all of themC) does not decrease for any of them D) does not increase for any of them

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Ans Key1.A 2.D 3.C 4.A 5.A 6.D 7.A 8.B


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9. All ideal gas, consisting of n moles, undergoes a reversible isothermal process during whichthe volume changes from Vi to Vf. The change in entropy of the thermal reservoir in contactwith the gas is given by:A) nR(Vf–Vi) B) nR ln(Vf–Vi) C) nRln(Vi/Vf) D) nRln(Vf/Vi)

10. One mole of an ideal gas expands slowly and isothermally at temperature T until its volume isdoubled. The change of entropy of this gas for this process is :A) R ln 2 B) (ln 2) /T C) 0 D) RT ln 2

11. An ideal gas, consisting of n moles, undergoes an irreversible process in which the tempera-ture has the same value at the beginning and end. If the volume changes from Vi to Vf, thechange in entropy of the gas is given by :A) nR(Vf–Vi) B) nR ln(Vf–Vi) C) nR ln(Vi/Vf) D) nR ln(Vf/Vi)

12. The temperature of n moles of a gas is increased from Ti to Tf at constant pressure. If themolar specific heat at constant pressure is Cp and is independent of temperature, then changein the entropy of the gas is :A) nCpln(Tf/Ti) B) nCpln(Ti/Tf)C) nCpln(Tf–Ti) D) nCpln(1–Ti/Tf)

13. Consider the following processes: The temperature of two identical gases are increased fromthe same initial temperature to the same temperature. Reversible processes are used. For gasA the process is carried out at constant volume while for gas B it is carried out at constantpressure. The change in entropy:A) is the same for A and BB) is greater for AC) is greater for BD) is greater for A only if the initial temperature is low

14. A hot object and a cold object are placed in thermal contact and the combination is isolated.They transfer energy until they reach a common temperature. The change DSh in the entropyof the hot object, the change DSC in the entropy of the cold object, and the change DStotal inthe entropy of the combination are :A) DSh>0,DSC>0,DStotal>0 B) DSh<0,DSC>0,DStotal>0C) DSh>0,DSC>0,DStotal<0 D) DSh>0,DSC<0,DStotal>0

15. Let SI denote the change in entropy of a sample for an irreversible process from state A tostate B. Let SR denote the change in entropy of the same sample for a reversible process fromstate A to state B. Then:A) SI>SR B) SI=SR C) SI<SR D) SI=0

9.C 10.A 11.D 12.A 13.C 14.B 15.B

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16. For all irreversible processes involving a system and its environment :A) the entropy of the system does not changeB) the entropy of the system increaseC) the total entropy of the system and its environment does not changeD) the total entropy of the system and its environment increases

17. According to the second law of thermodynamics :A) heat energy cannot be completely converted to workB) work cannot be completely converted to heat energyC) for all cyclic processes we have dQ/T<0D) the reason all heat engine efficiencies are less than 100% is friction, which is unavoidable

18. A Consider the following processes :I. Energy flows as heat from a hot object to a colder objectII. Work is done on a system and an equivalent amount of energy is rejected as heat by thesystemIII. Energy is absorbed as heat by a system and an equivalent amount of work is done by thesystemWhich are never found to occur ?A) Only I B) Only II C) Only III D)OnlyII and III

19. In a thermally insulated kitchen, an ordinary refrigerator is turned on and its door is left open.The temperature of the room :A) remains constant according to the first law of thermodynamicsB) increases according to the first law of thermodynamicsC) decreases according to the first law of thermodynamicsD) remains constant according to the second law of thermodynamics

20. A heat engine :A) converts heat input to an equivalent amount of workB) converts work to an equivalent amount of heatC) takes heat in, does work, and rejects heatD) uses positive work done on the system to transfer heat from a low temperature reservoirto a high temperature reservoid

21. A heat engine absorbs energy of magnitude |QH| as heat from a high temperature resevoir,does work of magnitude |W|, and rejects energy of magnitude |QL| as heat to a low tempera-ture reservoir. Its efficiency is:A) |QH|/|W| B) |QL|/|W| C)|QH|/|QL| D)|W|/|QH|

16.D 17.A 18.C 19.B 20.C 21.D

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22. A Carnot heat engine runs between a cold reservoir at temperature TC and a hot reservoir attemperature TH. You want to increase its efficiency. Of the following, which change results inthe greatest increase in efficiency? The value of DT is the same for all changes.A) Raise the temperature of the hot reservoir by DTB) Raise the temperature of the cold reservoir by DTC) Lower the temperature of the hot reservoir by DTD) Lower the temperature of the cold reservoir by DT

23. A certain heat engine draws 500 cal/s from a water bath at 270C and rejects 400 cal/s to areservoir at a lower temperature. The efficiency of this engine is :A) 80% B) 75 % C) 55% D) 20%

24. A heat engine that in each in each cycle does positive work and rejects energy as heat, withno heat energy input, would violate :A) the zeroth law of thermodynamics B) the first law of thermodynamicsC) the second law of thermodynamics D) the third law of thermodynamics

25. A cyclical process that transfers energy as heat from a high temperature reservoir to a lowtemperature reservoir with no other change would violate :A) the zeroth law of thermodynamics B) the first law of thermodynamicsC) the second law of thermodynamics D) none of the above

26. A heat engine in each cycle absorbs energy of magnitude |QH| as heat from a high tempera-ture reservoir, does work of magnitude |W|, and then absorbs energy of magnitude |QL| asheat from a low temperature reservoir. If |W| =|QH|+|QL| this engine violates :A) the zeroth law of thermodynamics B) the first law of thermodynamicsC) the second law of thermodynamics D) the third law of thermodynamics

27. A Carnot cycle :A) is bounded by two isotherms and two adiabats on a p–V graphB) consists of two isothermal and two constant volume processesC) is any four-sided process on a p–V graphD) only exists for an ideal gas

28. According to the second law of thermodynamics :A) all heat engines have the same efficiencyB) all reversible heat engines have the same efficiencyC) the efficiency of any heat engine is independent of its working substanceD) the efficiency of a Carnot engine depends only on the temperatures of the reservoirs

29. A Carnot heat engine operates between 2270C and 1270C. Its efficiency is :A) 20 % B) 25% C) 44% D) 79%

22.D 23.D 24.B 25.D 26.C 27.A 28.D 29.A

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30. A Carnot heat engine operates between a hot reservoir at absolute temperature T1 and a coldreservoir at absolute temperature T2. Its efficiency isA) T1/T2 B) T2/T1 C) 1–T1/T2 D) 1–T2/T1

31. A Carnot heat engine and an irreversible heat engine both operate between the same hightemperature and low temperature reservoirs. They absorb the same energy from the hightemperature reservoir as heat. The irreversible engine :A) does more workB) rejects more energy to the low temperature reservoir as heatC) has the greater efficiencyD) has the same efficiency as the reversible engine

32. A heat engine operates between 200 K and 100 K. In each cycle it takes 100 J from the hotreservoir, loses 25 J to the cold reservoir, and does 75J of work. This heat engine violates :A) both the first and second laws of thermodynamicsB) the first law but not the first law of thermodynamicsC) the second law but not the first law of thermodynamicsD) neither the first law nor the second law of thermodynamics

33. A refrigerator absorbs energy of magnitude |QC| as heat from a low temperature reservoirand rejects energy of magnitude |QH| as heat to a high temperature reservoir. Work W is doneon the working substance. The coefficient of performance is given by :A) |QC|/W B) |QH|/W C) (|QC|+|QH|)/W D) W/|QC|

34. A Carnot refrigerator operates between a low temperature reservoir at TC and a high tem-perature reservoir at TH. Its coefficient of performance is given by :A) (TH–TC)/TC B) TC/(TH–TC) C) (TH–TC )/TH D) TH(TH–TC)

35. An Carnot refrigerator runs between a cold reservoir at temperature TC and a hot reservoir attemperature TH. You want to increase its coefficient of performance. Of the following, whichchange results in the greatest increase in the coefficient ? The value of DT is the same for allchanges.A) Raise the temperature of the hot reservoir by DTB) Raise the temperature of the cold reservoir by DTC) Lower the temperature of the hot reservoir by DTD) Lower the temperature of the cold reservoir by DT

36. The most efficient heat engine would operate by taking heat at particular temperature and:A) Converting it all into workB) Converting some of it into work and rejecting the rest at a lower temperature

30.D 31.B 32.C 33.A 34.B 35.B

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C) Converting some of it into work and rejecting the rest at the same temperatureD) Converting some of it into work and rejecting the rest at a higher temperature

37. The most efficient heat engine is one which is:A) Reversible B) IrreversibleC) Driven by high speed diesel D) Driven by oil

38. An engine works between two temperatures 227oC and 27oC. The efficiency of the engine is:A) 40% B) 60% C) 80% D) 100%

39. An ideal heat engine exhausting heat at 27oC is to have 25% efficiency. It must take heat at:A) 127oC B) 227oC C) 327oC D) 673oC

40. A Carnot engine takes in 3000 kcal of heat from a reservoir at 627oC and gives it to a sink at27oC. The work done by the engine is:A) 4.2 106 J B) 8.4 106 J C) 16.8 106 J D) Zero

41. A Carnot engine working between 300 K and 600 K has a work output of 800 J per cycle. Theamount of heat energy supplied to the engine from the source in each cycle is:A) 800 J B) 1600 J C) 3500 J D) 6400 J

42. The efficiency of a railway engine is:A) 1% B) 10% C) 50% D) 100%

43. A cycle pump gets hot near the nozzle after a few quick storkes even if they are smoothbecause:A) The volume of air decreases at constant pressureB) The number of air molecules increasesC) The piston causes lot of frictionD) The process is so quick that exchange of heat with the environment does not take place.

An adiabatic compression causes increase in temperature

44. A carnot engine, having an efficiency of =1/10 as heat engine, is used as a refrigerator. Ifthe work done on the system is 10 J, the amount of energy absorbed from the reservoir atlower temperature is:A) 100 J B) 99 J C) 90 J D) 1 J

36.B 37.A 38.A 39.A 40.B 41.B 42.B 43.D 44.C

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45. A Carnot engine operates with source at 127oC and sink at 27oC. If the source supplies 40 kJof heat energy, the work done by the engine is:A) 30 kJ B) 10 kJ C) 4 kJ D) 1 kJ

46. A carnot engine uses first an ideal monoatomic gas 53

and then an ideal diatomic gas

73

as its working substance. The source and sink temperature are 4111oC and 69oC

respectively and the engine extracts 1000 J of heat from the source in each cycle, then:A) efficiencies of the engine in the two cases are in the ratio 21.25B) area enclosed by the P–V diagram in only the first case is 500 JC) area enclosed by the P–V diagram in both cases is 500 JD) heat rejected to the sink in the first case is 600 J while that in the second case is 713 J

47. A reversible heat engine converts one – sixth of the heat input into work. When the tempera-ture of the sink is reduced by 62oC, efficiency of the engine is doubled. Temperature of thesource and sink are:A) 80oC,37oC B) 99oC,37oC C) 95oC, 37oC D) 82oC,31oC

45.B 46.C 47.B

Second Law of Themodynamics

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