Solved Objective Examples on Thermodynamics

Level – l 

1. An intensive property is that property which depends upon

      (A) the nature of the substance                      

      (B) the amount of the substance

      (C) both the amount and nature of the substance

      (D) neither the nature nor the amount of the substance

2.    1255_equations.JPG in KJ/mol are respectively -393, -110, 81 and 34. Calculate ΔH in KJ of the following reaction.

      2NO2 (g) + 2CO (g) ——> N2O (g) + 3CO2(g)

      (A) 836                                                    (B) 1460

      (C) -836                                                   (D) -1460

3. Temperature of 1 mole of a gas is increased by 1° at constant pressure work done is

      (A) R                                             (B) 2R

      (C) R/2                                          (D) 3R

4. Which of the following thermodynamic quantities is an outcome of the second law of thermodynamics?

      (A) enthalpy                                   (B) internal energy

      (C) work                                         (D) entropy

5. The difference between heats of reaction at constant pressure and constant volume for the reaction

      2C6H6 (l) + 15O2 (g) ——> 12CO2 (g) + 6H2O (l) at 25°C in KJ mol-1 is

      (A) -7.43 KJmol-1                               (B) 7.43 KJmol-1      

      (C) 2.477 KJmol-1                              (D) -2.477 KJmol-1

6. For a reaction at equilibrium

      (A) ΔG = ΔGo ≠ 0                                (B) ΔGo = 0

      (C) ΔG = ΔGo = 0                                (D) ΔG = 0, ΔGo ≠ 0

7. When 1 mole gas is heated at constant volume, temperature is raised from 298 to 309 K. 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

8. In thermodynamics a process is called reversible when

      (A) surroundings and system change into each other

      (B) there is no boundary between system and surroundings

      (C) the surroundings are always in equilibrium with the system

      (D) the system changes into the surroundings spontaneously

9. What is true for the reaction?

      PCl6(g) ——> PCl3(g) + Cl2(g)

      (A) ΔH = ΔE                                          (B) ΔH > ΔE

      (C) ΔH < ΔE                                          (D) none

10. Calculate the work done when 1 mol of an ideal gas is compressed reversibly from 1.00 bar to 5.0 bar at a constant temperature of 300 K

      (A) -14.01 KJ                                        (B) 16.02 KJ

      (C) 4.01 KJ                                           (D) -8.02 KJ

11. The factor that does not influence the heat of reaction is

      (A) the physical state of reactants and products

      (B) the temperature

      (C) the pressure or volume

      (D) the method by which the final products are obtained

12. (ΔH – ΔE) for the formation of NH3 from N2­ and H2­ is

      (A) RT                                          (B) 2RT

      (C) -RT                                         (D) -2RT

13. A(l) ——> A(g), ΔHvap = 460.6 cal/mol boiling point = 50 k, what is boiling point at 10 atm?

      (A) 150 K                                       (B) 75 K

      (C) 100 K                                       (D) none

14. Heat of neutralization of H2C2O4 (oxalic acid) is -26 Kcal/mole. The dissociation energy of

      H2C2O4 ——> 2H+ + C2O4–2 is

      (A) 12.3 Kcal/mole                            (B) 1.4 Kcal/mole

      (C) -13.7 Kcal/mole                           (D) -1.4 Kcal/mole

15. The heats of combustion of yellow phosphorus and red phosphorous are –9.19 kJ and – 8.78 kJ respectively, then heat of transition of yellow phosphorus to red phosphorous is

       (A) – 18.69 kJ                                   (B) +1.13 kJ

       (C) +18.69 kJ                                    (D) 0.41 kJ

16. The enthalpies of formation of organic compounds are conveniently determined from their

      (A) boiling points                                 (B) melting points

      (C) enthalpies of neutralization             (D) enthalpies of combustion

17. Thermodynamic equilibrium involves

      (A) chemical equilibrium                        (B) thermal equation

      (C) mechanical equation                        (D) all the three

18. Evaporation of water is

      (A) a process in which neither heat is evolved nor absorbed

      (B) a process accompanied by chemical reaction

      (C) an exothermic change

      (D) an endothermic change 

19. The heat content of the system is called

      (A) internal energy                               (B) enthalpy

      (C) free energy                                    (D) entropy

20. The apparatus used for measuring the heat changes of a reaction is called

      (B) thermometer                                  (B) a colorimeter

      (C) a calorimeter                                  (D) none of these

The  questions given below consist of statements ‘Assertion’ (A) and ‘Reason’ (R).

(a) If both ‘A’ and ‘R’ are correct and ‘R’ is correct reason for ‘A’.

(b) If both ‘A’ and ‘R’ are correct but ‘R’ is not the correct explanation for ‘A’.

(c) If ‘A’ is true but ‘R’ is false.

(d) If both ‘A’ and ‘R’ are false.

21. (A) Enthalpy of graphite is lower than that of diamond.

      (R) Entropy of graphites lower than that of diamond.

22. (A) When a gas at high pressure expands against vacuum the work done is maximum.

      (R) Work done in expansion depends upon the pressure inside the gas & increase in volume.

23. (A) Molar entropy of vaporization of water is different form ethanol.

      (R) Water is more polar than methanol

24. (A) A reaction which is spontaneous & accompanied by decrease of randomness must be exothermic.

      (R) All exothermic reaction are accompanied by decrease of randomness.

25. (A) The enthalpy of formation of H2O(l) is greater than that of H2O(g).

      (R) Enthalpy change is negative for the condensation reaction.

      H2O(g) ———> H2O(l)

Solutions: 

Objective: 

Level – I  

            1.         D                2.         C                   3.         A        

            4.         D                5.         A                   6.         D        

            7.         B                8.         C                   9.         B        

            10.       C                11.       d                    12.       D        

            13.       C                14.       D                    15.       d

            16.       D                17.       D                    18.       D

            19.       B                20.       C                    21.       B

            22.       D                23.       B                    24.       C        

            25.       A

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