July, 2022Flame Institute

18. Entropy of a thermodynamic system does not change when this system is used for

(a) Conduction of heat from a hot reservoir to a cold reservoir (b) Conversion of heat into work isobarically (c) Conversion of heat into internal energy isochorically (d) Conversion of work into heat isochorically Ans. d (13)

17. In a reversible isochoric change

(a) ΔW = 0 (b) ΔQ = 0 (c) ΔT = 0 (d) ΔU …

15. How much work to be done in decreasing the volume of and ideal gas by an

(a) 28 joule (b) 27 joule (c) 25 joule (d) 24 joule Ans. d (4)

57. For an adiabatic expansion of a perfect gas, the value of ΔP/P is equal to

(a) -√γ ΔV/V (b) -ΔV/V (c) -γ ΔV/V (d) -γ2 ΔV/V Answer-c (7)

53.One mole of an ideal gas with γ=1.4 , is adiabatically compressed so that its temperature rises from 27°C to 35°C. The change in the internal energy of the gas is (R=8.3 J/mol K)

(a) –166 J (b) 166 J (c) –168 J (d) 168 J Answer-b (6)

13. A sample of gas expands from volume

V1 to V2 . The amount of work done by the gas is greatest when the expansion is (a) Isothermal (b) Isobaric (c) Adiabatic (d) Equal in all cases Ans. b (20)

12. Which of the following is correct in terms of increasing work done for the same initial and final state

(a) Adiabatic < Isothermal < Isobaric (b) Isobaric < Adiabatic < Isothermal (c) Adiabatic < Isobaric < Isothermal (d) None of these Ans. c (20)

22. An adiabatic process occurs at constant

(a) Temperature (b) Pressure (c) Heat (d) Temperature and pressure Explanation-(c) In adiabatic process, no heat transfers between system and surrounding. (7)

7. Unit mass of a liquid with volume

V1 is completely changed into a gas of volume V2 at a constant external pressure P and temperature T. If the latent heat of evaporation for the given mass is L, then the increase in the internal energy of the …

11. If 300 ml of a gas at 27°C is cooled to 7°C at constant pressure, then its final volume will be

(a) 540 ml (b) 350 ml (c) 280 ml (d) 135 ml Answer-c (18)

10. An ideal gas has volume

Vo at 27°C. It is heated at constant pressure so that its volume becomes 2Vo. The final temperature is (a) 54°C (b) 32.6°C (c) 327°C …

9. Two kg of water is converted into steam by boiling at atmospheric pressure. The volume changes from

2×10-3 m3 to 3.34 m3. The work done by the system is about (a) – 340 kJ (b) – 170 kJ (c) 170 kJ (d) 340 kJ Answer-d (4)

8. A gas expands

0.25m3 at constant pressure 103 N/m2 , the work done is (a) 2.5 ergs (b) 250 J (c) 250 W (d) 250 N Answer-b (6)

6. Work done by 0.1 mole of a gas at 27°C to double its volume at constant pressure is

(R = 2 cal mol–1 oC–1) (a) 54 cal (b) 600 cal (c) 60 cal (d) 546 cal Answer-c (9)

5. Work done by air when it expands from 50 litres to 150 litres at a constant pressure of 2 atmosphere is

(a) 2×104 joules (b) 2×100 joules (c) 2×105×100 joules (d) 2×10–5×100 joules Answer-a (8)

4. A gas is compressed at a constant pressure of

50 N/m2 from a volume of 10m3 to a volume of 4m3 . Energy of 100 J then added to the gas by heating. Its internal energy is (a) Increased by 400 J (b) Increased by 200 J (c) Increased …

3. One mole of a perfect gas in a cylinder fitted with a piston has a pressure P, volume V and temperature T. If the temperature is increased by 1 K keeping pressure constant, the increase in volume is

(a) 2V/273 (b) V/91 (c) V/273 (d) V …

2. When heat in given to a gas in an isobaric process, then

(a) The work is done by the gas (b) Internal energy of the gas increases (c) Both (a) and (b) (d) None from (a) and (b) Answer-c (5)

1. A gas expands under constant pressure P from volume

V1 to V2. The work done by the gas is (a) P(V2-V1) (b) P(V1-V2) (c) P(V1γ-V2γ) (d) (PV1V2)/(V2-V1) Answer-a (6)

56. Adiabatic modulus of elasticity of a gas is

2.1×105N/m2. What will be its isothermal modulus of elasticity[(Cp/Cv)=1.4] (a) 1.8×105N/m2 (b) 1.5×105N/m2 (c) 1.4×105N/m2 (d) 1.2×105N/m2 Answer-b (14)

55. During an adiabatic expansion of 2 moles of a gas, the change in internal energy was found –50J. The work done during the process is

(a) Zero (b) 100J (c) – 50J (d) 50J Answer-d (8)

54. The volume of a gas is reduced adiabatically to 1/4 of its volume at 27°C, if the value of γ=1.4 then the new temperature will be

(a) 350×40.4 K (b) 300×40.4 K (c) 150×40.4 K (d) None of these Answer-b (2)

52. A gas for which γ=1.5 is suddenly compressed to 1/4th of the initial volume. Then the ratio of the final to the initial pressure is

(a) 1 : 16 (b) 1 : 8 (c) 1 : 4 (d) 8 : 1 Answer-d (3)

51. A gas is suddenly compressed to one fourth of its original volume. What will be its final pressure, if its initial pressure is P

(a) Lesss than P (b) More than P (c) P (d) Either (a) or (c) Answer-b (5)

50. We consider a thermodynamic system. If ΔU represents the increase in its internal energy and W the work done by the system, which of the following statements is true

(a) ΔU=-W in an adiabatic process (b) ΔU=W in an isothermal process (c) ΔU=-W in an isothermal process (d) ΔU=W in an adiabatic process Answer-a (2)

49. The internal energy of the gas increases In

(a) Adiabatic expansion (b) Adiabatic compression (c) Isothermal expansion (d) Isothermal compression Answer-b (5)

48. A gas ( γ=1.3) is enclosed in an insulated vessel fitted with insulating piston at a pressure of

105 N/m2 . On suddenly pressing the piston the volume is reduced to half the initial volume. The final pressure of the gas is (a) 20.7 ×105 (b) 21.3 ×105 …

47. A gas is suddenly compressed to 1/4 th of its original volume at normal temperature. The increase in its temperature is(γ=1.5)

(a) 273 K (b) 573 K (c) 373 K (d) 473 K Answer-a (6)

46. One mole of an ideal gas at an initial temperature of T K does 6 R joules of work adiabatically. If the ratio of specific heats of this gas at constant pressure and at constant volume is 5/3, the final temperature of gas will be

(a) (T+2.4)K (b) (T-2.4)K (c) (T+4)K (d) (T-4)K Answer-d (8)

45. In adiabatic expansion of a gas

(a) Its pressure increases (b) Its temperature falls (c) Its density increases (d) Its thermal energy increases Answer-b (5)

44.During an adiabatic process, the pressure of a gas is found to be proportional to the cube of its absolute temperature. The ratio

Cp/Cv for the gas is (a) 3/2 (b) 4/3 (c) 2 (d) 5/3 Answer-a (10)

43. In an adiabatic process, the state of a gas is changed from

(P1,V1,T1) to (P2,V2,T2) . Which of the following relation is correct (a) T1V1γ-1=T2V2γ-1 (b) P1V1γ-1=P2V2γ-1 (c) T1P1γ=T2P2γ (d) T1V1γ=T2V2γ Answer-a (9)

42. If γ=2.5 and volume is equal to 1/8 times to the initial volume then pressure P’ is equal to (Initial pressure = P)

(a) P‘=P (b) P‘=2P (c) P‘=P ×215/2 (d) P‘=7P Answer-c (8)

41. Air is filled in a motor tube at 27°C and at a pressure of atmospheres. The tube suddenly bursts, then temperature of air is( given γ of air=1.5)

(a) 27.5°C (b) 75°K (c) 150K (d) 150°C Answer-c (3)

40. An ideal gas at a pressures of 1 atmosphere and temperature of 27°C is compressed adiabatically until its pressure becomes 8 times the initial pressure, then the final temperature is (γ = 3/2)

(a) 627°C (b) 527°C (c) 427°C (d) 327°C Answer-d (12)

39. ΔU + ΔW =0 is valid for

(a) Adiabatic process (b) Isothermal process (c) Isobaric process (d) Isochoric process Answer-a (4)

38. At 27°C a gas is suddenly compressed such that its pressure becomes 1/8 th of original pressure. Temperature of the gas will be(γ=5/3)

(a) 420K (b) 327°C (c) 300K (d) -142°C …

37. Two moles of an ideal monoatomic gas at 27°C occupies a volume of V. If the gas is expanded adiabatically to the volume 2V then the work done by the gas will be (γ=5/3,R=8.31J/mol K)

(a) -2767.23 J (b) 2767.23 J (c) 2500J (d) -2500J Answer-b (3)

36. The process in which no heat enters or leaves the system is termed as

(a) Isochoric (b) Isobaric (c) Isothermal (d) Adiabatic Answer-(d) In adiabatic process, no transfer of heat takes place between system and surrounding. (4)