CHAPTER THERMODYNAMICS

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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.

1 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 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: kj/mol 1412 kj/mol kj/mol 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.

2 55 quantities for a perfectly crystalline solid is zero at absolute zero? Free energy Entropy Enthalpy Internal energy 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 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 ) cal zero 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 JK 1 mol JK 1 mol JK 1 mol 1 20.

3 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 kj 731 kj 773 kj 229 kj kj kj kj kj Ans: kj 19 kj 10 kj 9 kj Ans: 196 kj/mol kj/mol 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 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) Ans: 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.

4 57 Jmol 1 J 1 K 1 mol 1 JKmol 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) 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 Pa Pa Pa Pa 33. Ans: RT + 3 RT Ans: kj kj + 261kJ 103 kj Ans: Considering entropy as a thermodynamic parameter, the criterion for the spontaneity of any process is J 608 J J 304 J 39. RT + RT

5 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: K 450 K 300 K K Ans: Ans: kj mol 1

59 425 kj mol 1 245 kj mol 1 290 kj mol 1 48.

6 kj mol kj mol kj mol and (IV) (II), (III) and (IV), (II) and (III) (II) and (III) Ans: Ans: K 1000 K 1250 K 500 K K 1110K 510K 710K Ans:

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.

7 kj/mol kj kj 43.3 kj 10.3 kj Ans: cal/ (mol K) cal/ (mol K) cal/ (mol K) cal/ (mol K) Ans: kj kj kj kj Ans: Ans: kj/mol 175 kj/mol 325 kj/mol Ans: 63.

8 V 3.0 V 2.5 V 5.0 V Ans: Ans: x = y z z = x + y x = y + z y = 2z x Ans:

10 NEET 31 Years 11. The enthalpy of fusion of water is kcal/mol. The molar entropy change for the melting of ice at

10 NEET 31 Years 11. The enthalpy of fusion of water is kcal/mol. The molar entropy change for the melting of ice at 6 Thermodynamics. A gas is allowed to expand in a well insulated container against a constant external pressure of.5 atm from an initial volume of.50 L to a final volume of 4.50 L. The change in internal