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CHAPTER

THERMODYNAMICS

1. If ΔH is the change in enthalpy and ΔE the change in internal energy accompanying a gaseous reaction, then (a) ΔHis always greater than ΔE (b) ΔH< ΔE only if the number of moles of the products is greater than the number of moles of the reactants (c) ΔH is always less than ΔE (d) ΔH< ΔE only if the number of moles of products is less than the number of moles of the reactants. Ans: (d) 2. Equal volumes of molar hydrochloric acid and sulphuric acid are neutralized by dil. NaOHsolution and x kcal and y kcal of heat are liberated respectively. Which of the following is true? (a) x = y (b) x = 1/2 (c) x = 2y (d) None of these Ans: (b) 3.

(a) ΔE+ 2RT (b) ΔE–2RT (c) ΔH= RT (d) ΔE– RT. Ans: (b) 4. During isothermal expansion of an ideal gas, its (a) internal energy increases (b) enthalpy decreases (c) enthalpy remains unaffected (d) enthalpy reduces to zero. Ans: (c) 5. Achemical reaction will be spontaneous if it is accompanied by a decrease of (a) entropy of the system (b) enthalpy of the system (c) internal energy of the system (d) free energy of the system Ans: (d) 6.

(a) +,–,+ (b) –, +, – (c) –, +, + (d) +, +, –. Ans: (b) 7.

(a) more cis-2 pentene is formed (b) equilibrium remains unaffected (c) additional trans-2 pentene is formed (d) equilibrium is shifted in forward direction Ans: (a) 8.

(a) – 141.2 kJ/mol (b) – 1412 kJ/mol (c) + 14.2 kJ/mol (d) + 1412 kJ/mol Ans: (b) 9. The correct relationship between free energy and equilibrium constant Kof a reaction is

(a)

(b)

(c) (d) Ans: (a)

10. According to the third law of

thermodynamics which one of the following

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quantities for a perfectly crystalline solid is zero at absolute zero? (a) Free energy (b) Entropy (c) Enthalpy (d) Internal energy Ans: (b) 11.

(a) +540.3 (b) +727.0 (c) –166.9 (d) +19.8 Ans: (d) 12. Hydrogen has an ionisation energy of 1311 kJ mol–1 and for chlorine it is 1256 kJmol–1. Hydrogen forms H+ (aq) ions but chlorine does not form Cl+ (aq) ions because (a) H+ has lower hydration enthalpy (b) Cl+ has lower hydration enthalpy (c) Cl has high electron affinity (d) Cl has high electronegativity Ans: (b) 13.

(a)

(b)

(c)

(d) Ans: (b) 14. Identify the correct statement regarding entropy: (a) At absolute zero of temperature, entropy of a perfectly crystalline substance is taken to be zero (b) At absolute zero of temperature, the entropy of a perfectly crystalline substance is +ve

(c) At absolute zero of temperature, the entropy of all crystalline substances is taken to be zero (d) At 0ºC, the entropy of a perfectly crystalline substance is taken to be zero Ans: (a) 15. One mole of an ideal gas at 300 Kis expanded isothermally from an initial volume of 1 litre to 10 litres. The 'Efor this process is (R=2 cal. mol–1 K–1) (a) 163.7 cal (b) zero (c) 1381.1 cal (d) 9 lit. atm Ans: (b) 16. For a cyclic process, which of the following is not true? (a) ΔH= 0 (b) ΔE= 0 (c) ΔG= 0 (d) Total W= 0 Ans: (d) 17. Adiabatic expansions of an ideal gas is accompanied by (a) decrease in ΔE (b) increase in temperature (c) decrease in ΔS (d) no change in any one of the above properties Ans: (a) 18. For a reaction in which all reactants and products are liquids, which one of the following equations is most applicable? (a) ΔH< ΔE (b) ΔH= ΔS (c) ΔH= ΔE (d) ΔH= ΔG Ans: (c) 19. The entropy change in the fusion of one mole of a solid melting at 27ºC(Latent heat of fusion, 2930 Jmol–1) is: (a) 9.77 JK–1 mol–1 (b) 10.73 JK–1 mol–1 (c) 2930 JK–1 mol–1 (d) 108.5 JK–1 mol–1 Ans: (a) 20.

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(a) –357 kJ (b) –731 kJ (c) –773 kJ (d) –229 kJ Ans: (b) 21.

(a) –200 kJ (b) –356.2 kJ (c) + 200 kJ (d) – 396.2 kJ Ans: (c) 22.

(a) 28 kJ (b) 19 kJ (c) – 10 kJ (d) 9 kJ Ans: (c) 23.

(a) x > y (b) x < y (c) x = y (d) x ≥ y

Ans: (a) 24. When 1 mol of a gas is heated at constant volume, temperature is raised from 298 to 308 K. If heat supplied to the gas is 500 J, then which statement is correct? (a) q = w = 500 J, ΔU= 0 (b) q = ΔU= 500 J, w = 0 (c) q = –w = 500 J, ΔU= 0 (d) ΔU= 0, q = w = –500 J Ans: (b) 25.

(a) –196 kJ/mol (b) + 948 kJ/mol (c) + 196 kJ/mol (d) –948 kJ/mol Ans: (a) 26. In a closed insulated container, a liquid is stirred with a paddle to increase the temperature, which of the following is true? (a) ΔE = W ≠ 0,q = 0 (b) ΔE = W = q ≠ 0 (c) ΔE=0,W=q ≠ 0 (d) W=0, ΔE = q ≠ 0 Ans: (a) 27. 2 mole of an ideal gas at 27ºCtemperature is expanded reversibly from 2 lit to 20 lit. Find the entropy change (R= 2 cal/mol K) (a) 92.1 (b) 0 (c) 4 (d) 9.2 Ans: (d) 28.

(a) –17 kcal (b) – 111 kcal (c) –170 kcal (d) –85 kcal Ans: (a) 29. Unit of entropy is (a) JK–1 mol–1

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(b) Jmol–1 (c) J–1 K–1 mol–1 (d) JKmol–1 Ans: (a) 30. The molar heat capacity of water at constant pressure is 75 JK–1 mol–1. When 1kJ of heat is supplied to 100 g of water, which is free to expand, the increase in temperature of water is (a) 6.6 K (b) 1.2 K (c) 2.4 K (d) 4.8 K Ans: (c) 31. What is the entropy change (in JK–1 mol–1) when one mole of ice is converted into water at 0º C? (The enthalpy change for the conversion of ice to liquid water is 6.0 kJmol–1 at 0ºC) (a) 21.98 (b) 20.13 (c) 2.013 (d) 2.198 Ans: (a) 32. The densities of graphite and diamond at 298 Kare 2.25 and 3.31 g cm–3, respectively. If the standard free energy difference (ΔGº) is equal to 1895 Jmol–1, the pressure at which graphite will be transformed into diamond at 298 Kis (a) 9.92 × 105 Pa (b) 9.92 × 108 Pa (c) 9.92 × 107 Pa (d) 9.92 × 106 Pa Ans: (b) 33.

(a)

(b)

(c)

(d) Ans: (d) 34.

(a) – RT (b) + RT

(c) – 3 RT (d) + 3 RT Ans: (c) 35.

(a) – 261 kJ (b) + 103 kJ (c) + 261kJ (d) – 103 kJ Ans: (d) 36.

(a)

(b)

(c)

(d) Ans: (b) 37. Considering entropy as a thermodynamic parameter, the criterion for the spontaneity of any process is

(a)

(b)

(c)

(d) Ans: (a) 38.

(a) – 6 J (b) – 608 J (c) + 304 J (d) – 304 J Ans: (b) 39.

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(a) (b)

(c)

(d) Ans: (c) 40.

(a)

(b)

(c)

(d) Ans: (c) 41. Which of the following pairs of a chemical reaction is certain to result in a spontaneous reaction? (a) Exothermic and increasing disorder (b) Exothermic and decreasing disorder (c) Endothermic and increasing disorder (d) Endothermic and decreasing disorder Ans: (a) 42.

(a) (b) (c)

(d) Ans: (a) 43.

(a) 273 K (b) 450 K (c) 300 K (d) 285.7 K Ans: (d) 44.

(a)

(b)

(c)

(d) Ans: (a) 45.

(a)

(b)

(c)

(d) Ans: (d) 46.

(a)

(b)

(c)

(d) Ans: (d) 47.

(a) 380 kJ mol–1

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(b) 425 kJ mol–1 (c) 245 kJ mol–1 (d) 290 kJ mol–1 Ans: (b) 48.

(a) and (IV) (b) (II) , (III) and (IV) (c) , (II) and (III) (d) (II) and (III) Ans: (d) 49.

(a)

(b)

(c)

(d) Ans: (b) 50.

(a)

(b)

(c)

(d) Ans: (c) 51.

(a) 910K (b) 1110K (c) 510K (d) 710K Ans: (b) 52.

(a)

(b)

(c)

(d) Ans: (b) 53.

(a) 750 K (b) 1000 K (c) 1250 K (d) 500 K Ans: (a) 54.

(a) (b) (c) (d) Ans: (d) 55.

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(a) + 6.2 kJ (b) + 10.3 kJ (c) – 43.3 kJ (d) – 10.3 kJ Ans: (a) 56.

(a)

(b)

(c)

(d) Ans: (d) 57.

(a) – 434.8 kJ (b) – 869.6 kJ (c) + 434.8 kJ (d) + 217.4 kJ Ans: (c) 58.

(a) 525 kJ/mol (b) – 175 kJ/mol (c) – 325 kJ/mol

(d) 325 kJ/mol Ans: (b) 59.

(a)

(b)

(c)

(d) Ans: (a) 60.

(a) 10.52 cal/ (mol K) (b) 21.04 cal/ (mol K) (c) 5.260 cal/ (mol K) (d) 0.526 cal/ (mol K) Ans: (c) 61.

(a) + 37.56 (b) – 43.76 (c) + 43.76 (d) + 40.66 Ans: (d) 62.

(a) 0.83 (b) 1.50 (c) 3.3 (d) 1.67 Ans: (d) 63.

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(a) 4.5 V (b) 3.0 V (c) 2.5 V (d) 5.0 V Ans: (c) 64.

(a) 32 (b) 38 (c) 317 (d) 477 Ans: (c) 65.

(a) x = y – z (b) z = x + y (c) x = y + z (d) y = 2z – x Ans: (c) 1.

2.

3.

4.

5.

6.

7.

8.

9.

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10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

23.

24.

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25.

26.

27.

28.

29.

30.

31.

32.

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33.

34.

35.

36.

37.

38.

39.

40.

41.

42.

43.

44.

45.

46.

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47.

48.

49.

50.

51.

52.

53.

54.

55.

56.

57.

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58.

59.

60.

61.

62.

63.

64.

65.