CHAPTER THERMODYNAMICS

54 CHAPTER THERMODYNAMICS 1. If ΔH is the change in enthalpy and ΔE the change in internal energy accompanying a gaseous reaction, then ΔHis always greater than ΔE ΔH< ΔE only if the number of moles of the products is greater than the number of moles of the reactants ΔH is always less than ΔE ΔH< ΔE only if the number of moles of products is less than the number of moles of the reactants. Ans: 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? x = y x = 1/2 x = 2y None of these +,,+, +,, +, + +, +,. 7. more cis-2 pentene is formed equilibrium remains unaffected additional trans-2 pentene is formed equilibrium is shifted in forward direction 8. 3. ΔE+ 2RT ΔE 2RT ΔH= RT ΔE RT. 4. During isothermal expansion of an ideal gas, its internal energy increases enthalpy decreases enthalpy remains unaffected enthalpy reduces to zero. Ans: 5. Achemical reaction will be spontaneous if it is accompanied by a decrease of entropy of the system enthalpy of the system internal energy of the system free energy of the system Ans: 6. 141.2 kj/mol 1412 kj/mol + 14.2 kj/mol + 1412 kj/mol 9. The correct relationship between free energy and equilibrium constant Kof a reaction is 10. According to the third law of thermodynamics which one of the following

55 quantities for a perfectly crystalline solid is zero at absolute zero? Free energy Entropy Enthalpy Internal energy 11. +540.3 +727.0 166.9 +19.8 Ans: 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 H + has lower hydration enthalpy Cl + has lower hydration enthalpy Cl has high electron affinity Cl has high electronegativity 13. 14. Identify the correct statement regarding entropy: At absolute zero of temperature, entropy of a perfectly crystalline substance is taken to be zero At absolute zero of temperature, the entropy of a perfectly crystalline substance is +ve At absolute zero of temperature, the entropy of all crystalline substances is taken to be zero At 0ºC, the entropy of a perfectly crystalline substance is taken to be zero 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 ) 163.7 cal zero 1381.1 cal 9 lit. atm 16. For a cyclic process, which of the following is not true? ΔH= 0 ΔE= 0 ΔG= 0 Total W= 0 Ans: 17. Adiabatic expansions of an ideal gas is accompanied by decrease in ΔE increase in temperature decrease in ΔS no change in any one of the above properties 18. For a reaction in which all reactants and products are liquids, which one of the following equations is most applicable? ΔH< ΔE ΔH= ΔS ΔH= ΔE ΔH= ΔG Ans: 19. The entropy change in the fusion of one mole of a solid melting at 27ºC(Latent heat of fusion, 2930 Jmol 1 ) is: 9.77 JK 1 mol 1 10.73 JK 1 mol 1 2930 JK 1 mol 1 108.5 JK 1 mol 1 20.

56 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? q = w = 500 J, ΔU= 0 q = ΔU= 500 J, w = 0 q = w = 500 J, ΔU= 0 ΔU= 0, q = w = 500 J 25. 357 kj 731 kj 773 kj 229 kj 21. 200 kj 356.2 kj + 200 kj 396.2 kj Ans: 22. 28 kj 19 kj 10 kj 9 kj Ans: 196 kj/mol + 948 kj/mol + 196 kj/mol 948 kj/mol 26. In a closed insulated container, a liquid is stirred with a paddle to increase the temperature, which of the following is true? ΔE = W 0,q = 0 ΔE = W = q 0 ΔE=0,W=q 0 W=0, ΔE = q 0 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) 92.1 0 4 9.2 Ans: 28. 23. x > y x < y x = y x y 17 kcal 111 kcal 170 kcal 85 kcal 29. Unit of entropy is JK 1 mol 1

57 Jmol 1 J 1 K 1 mol 1 JKmol 1 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 6.6 K 1.2 K 2.4 K 4.8 K Ans: 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) 21.98 20.13 2.013 2.198 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 9.92 10 5 Pa 9.92 10 8 Pa 9.92 10 7 Pa 9.92 10 6 Pa 33. Ans: 34. 3 RT + 3 RT Ans: 35. 261 kj + 103 kj + 261kJ 103 kj Ans: 36. 37. Considering entropy as a thermodynamic parameter, the criterion for the spontaneity of any process is 38. 6 J 608 J + 304 J 304 J 39. RT + RT

58 Ans: 40. Ans: 41. Which of the following pairs of a chemical reaction is certain to result in a spontaneous reaction? Exothermic and increasing disorder Exothermic and decreasing disorder Endothermic and increasing disorder Endothermic and decreasing disorder 45. Ans: 46. 42. 43. 273 K 450 K 300 K 285.7 K Ans: Ans: 47. 44. 380 kj mol 1

59 425 kj mol 1 245 kj mol 1 290 kj mol 1 48. and (IV) (II), (III) and (IV), (II) and (III) (II) and (III) Ans: 49. 50. Ans: 53. 750 K 1000 K 1250 K 500 K 54. 51. 910K 1110K 510K 710K Ans: 55. 52.

60 325 kj/mol 59. + 6.2 kj + 10.3 kj 43.3 kj 10.3 kj 56. 60. Ans: 57. 10.52 cal/ (mol K) 21.04 cal/ (mol K) 5.260 cal/ (mol K) 0.526 cal/ (mol K) Ans: 61. 434.8 kj 869.6 kj + 434.8 kj + 217.4 kj Ans: 58. + 37.56 43.76 + 43.76 + 40.66 Ans: 62. 525 kj/mol 175 kj/mol 325 kj/mol 0.83 1.50 3.3 1.67 Ans: 63.

61 3. 4. 4.5 V 3.0 V 2.5 V 5.0 V Ans: 64. 5. 6. 32 38 317 477 Ans: 65. 7. 8. x = y z z = x + y x = y + z y = 2z x Ans: 9. 1. 2.

62 18. 10. 19. 11. 20. 12. 13. 21. 22. 14. 23. 15. 16. 17. 24.

63 25. 26. 29. 27. 30. 28. 31. 32.

64 42. 33. 34. 35. 43. 36. 44. 37. 38. 45. 39. 40. 46. 41.

65 47. 52. 48. 53. 49. 54. 50. 55. 56. 51. 57.

66 58. 64. 59. 65. 60. 61. 62. 63.