CHEMICAL THERMODYNAMICS – 4

1) Two moles of an ideal gas expand spontaneously into a vacuum. The work done is
a) zero
b) 2 J
c) 4 J
d) 8 J

2) The enthalpy of vaporisation of a substance is 840 J / mol and its boiling point is -1730C. Its entropy of vaporisation is
a)
b)
c)
d)

3) The enthalpy changes at 298 K in successive breaking of O — H bonds of HOH are
H2O (g) H (g) + OH (g), = 498 kJ / mole
OH (g) H (g) + O (g), = 428 kJ / mole.The bond enthalpy of the O — H bonds of HOH are

a) 498 kJ / mol
b) 463 kJ / mol
c) 428 kJ / mol
d) 70 kJ / mol

4) The bond energy of an O — H bond is 109 kcal / mol. When a mole of water is formed
a) 218 kcal is released
b) 109 kcal is released
c) 218 kcal is absorbed
d) 109 kcal is absorbed

5) The energy required to dissociate 4 g of gaseous hydrogen into free gaseous atoms is 208 kcal at 250 C. The bond energy of the H — H bond will be
a) 104 kcal
b) 10.4 kcal
c) 1040 kcal
d) 1.04 kcal

6) Heat evolved in the reaction H2 + Cl2 2 HCl is 182 kJ.Bond energies H -H = 430 kJ / mole, Cl-Cl = 242 kJ / mole. The H -Cl bond energy is
a) 763 kJ / mole
b) 427 kJ / mole
c) 336 kJ / mole
d) 154 kJ / mole

7) One mole of an ideal gas at 300 K is expanded isothermally from an initial volume of 1 litre to 10 litres. The E for this process is ( R = 2 cal mole-1 K-1 )
a) 163.7 cal
b) zero
c) 1381.1 cal
d) 9 lit atom.

8) The reaction 2SO2 + O2 2SO3; D H =-ve. Yield at equilibrium is favoured by
a) Low temperature and low pressure
b) Low temperature and high pressure
c) High temperature and low pressure
d) High temperature and high pressure

9) Amongst the following chemical reactions, the irreversible reaction is
a)
b)
c)
d)

10) For maximum production of SO3 in the reaction, 2SO2 + O2 ® 2SO3; D H = – Q.cals, the favourable conditions will be
a) High temperature and high pressure
b) Low temperature and high pressure
c) High temperature and low pressure
d) Low temperature and low pressure

11) For maximum production of NH3 in the reaction, N2 + 3H2 2NH3 + Q k.cals, the favourable conditions will be
a) Low temperature and low pressure
b) High temperature and low pressure
c) Low temperature and high pressure
d) High temperature and high pressure

12) 240 g. of urea are present in 10 litre solution. The active mass of urea will be
a) 0.2
b) 0.06
c) 0.4
d) 0.08

13) Which one of the following reversible reactions cannot be affected by pressure?
a)
b)
c)
d)

14) For which of the following reactions Kp = Kc?
a)
b)
c)
d)

15) The equilibrium constant for the reversible reaction N2 + 3H2 2NH3 is K and for reaction 1/2 N2 + 3/2 H2 NH3, the equilibrium constant is K. The K and K will be related as
a)
b)
c)
d)

16) An equilibrium mixture of the reaction 2H2S(g) 2H2 (g) + S2(g) had 0.5 mole H2S, 0.10 mole H2 and 0.4 mole S2 in one litre vessel. The value of the equilibrium constant (K) in mole litre-1 is
a) 0.004
b) 0.008
c) 0.016
d) 0.160

17) A quantity of PCl5 was heated in a 10 litre vessel at 250°C. PCl 5 (g) PCl 3 (g)+Cl 2(g). At equilibrium the vessel contains 0.1 mole of PCl5, 0.2 mole of PCl 3 and 0.2 mole of Cl2. The equilibrium constant of the reaction is
a) 0.02
b) 0.05
c) 0.04
d) 0.025

18) If k1 and K2 are the equilibrium constants of equilibrium (i) and (ii) respectively, what is the relationship between the two constants

(i) SO2(g)+l/2O2(g) SO3(g);K1

(ii) 2SO3(g) 2SO2(g) + O2(g);K2
a)
b)
c)
d)

19) If K1 is the equilibrium constant for the reaction 2NH3 N2 + 3H2, then the equilibrium constant for the reaction 1/2N2 + 3/2H2 NH3 would be
a)
b)
c)
d)

20) For a gaseous reaction involving complete combustion of isobutylene
a) D H < D E
b) D H = D E

c) D H > D E

d) D H = 0, D E = 0

21) The minimum energy necessary for a reaction to occur is the
a) Internal energy
b) Threshold energy
c) Activation energy
d) Free energy

22) One would expect a protein to have a very large
a) Ionization potential
b) Radius
c) Charge
d) Hydration energy

23) A property of a system that is dependent upon the amount of the substance present in the system is called an
a) Extensive property
b) Intensive property
c) Physical property
d) Thermal property

24) A liquid is in equilibrium with its vapours at its boiling point. On an average the molecules in the two phases have equal
a) Intermolecular energy
b) Potential energy
c) Total energy
d) Kinetic energy

25) The enthalpy change of a reaction does not depend on the
a) Conditions of a reaction
b) Initial and final concentrations
c) Physical states of reactant and products
d) Reaction path

26) The heat change for the reaction CO2 ( S ) « CO2 ( g )  is called the
a) Heat of fusion
b) Heat of reaction
c) Heat of vapourisation
d) Heat of sublimation

27) The amount of heat evolved when one mole of CH3 COOH reacts with one mole of NaOH is
a) 13. 7 Kcal mole-1

b) Less than 13. 7 Kcal mole-1

c) More than 13. 7 Kcal mole-1

d) None of these

28) The process in which pressure remains constant throughout a change is
a) Adiabatic
b) Isochoric
c) Isobaric
d) Isothermal

29) Which represents the larger amount of energy?
a) Calorie
b) Erg
c) Joule
d) Electron volt

30) Show what percent T1 is of T2 for a heat engine whose ideal efficiency is 10% .
a) 95%
b) 90%
c) 92%
d) 90%

31) An adiabatic process is one in which
a) q = O
b) Q = Pd V
c) D E = W

d) D E < Vd P

32) When a solid melts there is
a) An increase in enthalpy
b) A decrease in enthalpy
c) No change in enthalpy
d) A decrease in internal energy

33) Thermodynamic equilibrium involves
a) Chemical equilibrium
b) Thermal equilibrium
c) Mechanical equilibrium
d) Chemical equilibrium,Thermal equilibrium, Mechanical equilibrium

34) The entropy change when one gram of ice at 0 deg C melts is

a) 0. 92 Cal per degree per gram
b) 0. 29 Cal per degree per gram
c) 29 Cal per degree per gram
d) 2. 9 Cal per degree per gram

35) Beckmann method is used to measure
a) p
b)
c) Tb
d) Tf


Answer :

Ans 1) a

Ans Desc 1) =0, W = PD V = 0.

Ans 2) a

Ans Desc 2)

Ans 3) b

Ans Desc 3) Average value = (498 + 428)/2 = 463 kJ

Ans 4) a

Ans Desc 4) Energy absorbed in the dissociation of 1 mole of =2 x 109 = 218 kcal.This will be the energy released when 1 mole of is formed.

Ans 5) a

Ans Desc 5) 4 g =2 moles. Bond energy for 1 mole of =208/2 = 104 kcal

Ans 6) b

Ans Desc 6)
-182 = 430 + 242 – 2 B.E. (HCI)
B.E. (HCI) = 427 kJ

Ans 7) b

Ans Desc 7) For isothermal expansion of ideal gas, D E = O

Ans 8) b

Ans Desc 8) The reaction is exothermic so it will be favoured by low temperature. The reaction takes place with decrease in volume. So it will be favoured by high pressure. Thus conditions are low temperature and high pressure.

Ans 9) b

Ans Desc 9) Ionic reactions are very fast and takes place instantaneously. A precipitate of AgCl is immediately formed when AgNO3 is added to NaCl solution.

Ans 10) b

Ans Desc 10) The reaction is exothermic so it will be favoured by low temperature. The reaction takes place with decrease in volume. So it will be favoured by high pressure. Thus conditions are low temperature and high pressure.

Ans 11) c

Ans Desc 11) The reaction is exothermic and takes place with decrease in volume. Thus favourable conditions are low temperature and high pressure.

Ans 12) c

Ans Desc 12) Active mass 240/60×0.10=0.4 mol/litre

Ans 13) a

Ans Desc 13) Pressure has no effect on such reactions which take place with no change in volumes.

Ans 14) b

Ans Desc 14) :. For this reaction D n = 2 -2 = 0. Thus Kp = Kc

Ans 15) b

Ans Desc 15)

Ans 16) c

Ans Desc 16)

2H2S(g) 2H2(g) + S2 (g)

2 0.5 20.10 0.4

= 0.20.20.4 = 0.016

Ans 17) c

Ans Desc 17)

PCl5 PCl3 + Cl2

0.1 0.2 0.2

Ans 18) a

Ans Desc 18)

SO2 (g) + 1/2 O2 (g) SO3(g); K1

2SO3(g) 2SO2(g) + O2(g) ; K2

[K1]2=l/K2 or K1=

Ans 19) c

Ans Desc 19) The reations is exothermic so it will be favoured by low temperature.The reaction takesplace with decrease in volume.So it will be favoured by high pressure.Thus conditions are low teperatures and high pressure.

Ans 20) a

Ans Desc 20)

Ans 21) b

Ans Desc 21)

Ans 22) d

Ans Desc 22)

Ans 23) a

Ans Desc 23)

Ans 24) d

Ans Desc 24)

Ans 25) d

Ans Desc 25)

Ans 26) d

Ans Desc 26)

Ans 27) b

Ans Desc 27)

Ans 28) c

Ans Desc 28)

Ans 29) a

Ans Desc 29)

Ans 30) b

Ans Desc 30)

Ans 31) a

Ans Desc 31)

Ans 32) a

Ans Desc 32)

Ans 33) d

Ans Desc 33)

Ans 34) b

Ans Desc 34)

Ans 35) d

Ans Desc 35)

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