2022Flame Institute

26. The latent heat of vaporisation of water is 2240 J/gm. If the work done in the process of expansion of 1 g is 168 J, then increase in internal energy is

25. When 1 gm of water at 0°C and

1×105 N/m2 pressure is converted into ice of volume 1.091 cm3 , the external work done will be (a) 0.0091 joule (b) 0.0182 joule (c) – 0.0091 joule (d) – 0.0182 joule Answer-a (5)

24. When heat is given to a gas in an isothermal change, the result will be

(a) External work done (b) Rise in temperature (c) Increase in internal energy (d) External work done and also rise in temp. Answer-a (5)

22. If an ideal gas is compressed isothermally then

(a) No work is done against gas (b) Heat is relased by the gas (c) The internal energy of gas will increase (d) Pressure does not change Explanation-(b) In isothermal process, heat is released by the gas to maintain the …

21. A thermodynamic process in which temperature T of the system remains constant though other variable P and V may change, is called

(a) Isochoric process (b) Isothermal process (c) Isobaric process (d) None of these Explanation-(b) In isothermal process, temperature remains constant. (6)

20. In an isothermal process the volume of an ideal gas is halved. One can say that

(a) Internal energy of the system decreases (b) Work done by the gas is positive (c) Work done by the gas is negative (d) Internal energy of the system increases Answer-c (5)

19. A container that suits the occurrence of an isothermal process should be made of

(a) Copper (b) Glass (c) Wood (d) Cloth Explanation-(a) An isothermal process takes place at constant temperature, must be carried out in a vessel with conducting wall so that heat generated should go out at once. (7)

18. A thermally insulated container is divided into two parts by a screen. In one part the pressure and temperature are P and T for an ideal gas filled. In the second part it is vacuum. If now a small hole is created in the screen, then the temperature of the gas will

(a) Decrease (b) Increase (c) Remain same (d) None of the above Answer-c (10)

17. The specific heat of a gas in an isothermal process is

(a) Infinite (b) Zero (c) Negative (d) Remains constant Answer-a (12)

15. In isothermic process, which statement is wrong

(a) Temperature is constant (b) Internal energy is constant (c) No exchange of energy (d) (a) and (b) are correct Explanation-(c) In isothermal process, exchange of energy takes place between system and surrounding to maintain the system temperature constant. (13)

14. In an isothermal change, an ideal gas obeys

(a) Boyle’s law (b) Charle’s law (c) Gaylussac law (d) None of the above Answer-a (13)

13. The isothermal bulk modulus of a perfect gas at normal pressure is

(a) 1.013×105 N/m2 (b) 1.013×106 N/m2 (c) 1.013×10-11 N/m2 (d) 1.013×1011 N/m2 Answer-a (9)

10. Work done per mol in an isothermal change is

(a) RT log10 (V2/V1) (b) RT log10 (V1/V2) (c) RT loge (V2/V1) (d) RT loge (V1/V2) Answer-c (12)

59. The average kinetic energy of hydrogen molecules at 300 K is E. At the same temperature, the average kinetic energy of oxygen molecules will be

(a) E/4 (b) E/16 (c) E (d) 4 E Answer-c (8)

12. In isothermal expansion, the pressure is determined by

(a) Temperature only (b) Compressibility only (c) Both temperature and compressibility (d) None of these Answer-b (7)

11. The isothermal Bulk modulus of an ideal gas at pressure P is

(a) P (b) γ (c) P / 2 (d) P /γ Answer-a (9)

9. If a gas is heated at constant pressure, its isothermal compressibility

(a) Remains constant (b) Increases linearly with temperature (c) Decreases linearly with temperature (d) Decreases inversely with temperature Answer-a (12)

8. One mole of

O2 gas having a volume equal to 22.4 litres at 0°C and 1 atmospheric pressure in compressed isothermally so that its volume reduces to 11.2 litres. The work done in this process is (a) 1672.5 J …

7. The gas law (PV)/T constant is true for

(a) Isothermal changes only (b) Adiabatic changes only (c) Both isothermal and adiabatic changes (d) Neither isothermal nor adiabatic changes Answer-c (8)

6. For an isothermal expansion of a perfect gas,

the value of ΔP/P is equal (a) – γ1/2 ΔV/V (b) -(ΔV/V) (c) -γ1 ΔV/V (d) -γ2 ΔV/V Ans. b (7)

5. A vessel containing 5 litres of a gas at 0.8 m pressure is connected to an evacuated vessel of volume 3 litres. The resultant pressure inside will be (assuming whole system to be isolated)

(a) 4/3 m (b) 0.5 m (c) 2.0 m (d) 3/4 m Ans. b (8)

4. In an isothermal reversible expansion, if the volume

of 96 gm of oxygen at 27°C is increased from 70 litres to 140 litres, then the work done by the gas will be (a) 300 R log102 (b) 81 R loge2 …

3. In an isothermal expansion

(a) Internal energy of the gas increases (b) Internal energy of the gas decreases (c) Internal energy remains unchanged (d) Average kinetic energy of gas molecule decreases Ans. c (12)

2. Can two isothermal curves cut each other

(a) Never (b) Yes (c) They will cut when temperature is 0°C (d) Yes, when the pressure is critical pressure Ans. a (8)

1. For an ideal gas, in an isothermal process

(a) Heat content remains constant (b) Heat content and temperature remain constant (c) Temperature remains constant (d) None of the above Ans. c (11)

48. Which of the following is incorrect regarding the first law of thermodynamics

(a) It introduces the concept of the internal energy (b) It introduces the concept of the entropy (c) It is not applicable to any cyclic process (d) None of the above Ans. b (20)

47. If a system undergoes contraction of volume then the work done by the system will be

(a) Zero (b) Negligible (c) Negative (d) Positive Ans. c (5)

46. A perfect gas goes from state A to another state B by absorbing

8 x 105 J of heat and doing 6.5 x 105 J of external work. It is now transferred between the same two states in another process in which it absorbs 105J of heat. Then in the second process (a) Work done …