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#### UNIT TEST 8

11th Standard

Reg.No. :
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Chemistry

Time : 03:00:00 Hrs
Total Marks : 150

PART -A

25 x 1 = 25
1. If Kb and Kf for a reversible reactions are 0.8 ×10–5 and 1.6 × 10–4 respectively, the value of the equilibrium constant is,

(a)

20

(b)

0.2 x 10-4

(c)

0.05

(d)

none of these

2. At a given temperature and pressure, the equilibrium constant values for the equilibria
${ 3A }_{ 2 }+{ B }_{ 2 }+2C\overset { { K }_{ 1 } }{ \rightleftharpoons } { 2A }_{ 3 }BC$ and
${ A }_{ 3 }BC\overset { { K }_{ 2 } }{ \rightleftharpoons } 3/2\left[ { A }_{ 2 } \right] +\frac { 1 }{ 2 } { B }_{ 2 }+C$
The relation between K1 and K2 is

(a)

$K_1={1\over \sqrt{K_2}}$

(b)

$K_2=K_1^{-1/2}$

(c)

$K_1^2=2K_2$

(d)

${K_1\over 2}=K_2$

3. The equilibrium constant for a reaction at room temperature is K1 and that at 700 K is K2. If K1 > K2, then

(a)

The forward reaction is exothermic

(b)

The forward reaction is endothermic

(c)

The reaction does not attain equilibrium

(d)

The reverse reaction is exothermic

4. The formation of ammonia from N2(g) and H2(g) is a reversible reaction
N2(g) + 3H2(g) ⇌ 2NH3(g) + Heat
What is the effect of increase of temperature on this equilibrium reaction

(a)

equilibrium is unaltered

(b)

formation of ammonia is favoured

(c)

equilibrium is shifted to the left

(d)

reaction rate does not change

5. Solubility of carbon dioxide gas in cold water can be increased by

(a)

increase in pressure

(b)

decrease in pressure

(c)

increase in volume

(d)

none of these

6. Which one of the following is incorrect statement?

(a)

for a system at equilibrium, Q is always less than the equilibrium constant

(b)

equilibrium can be attained from either side of the reaction

(c)

presence of catalyst affects both the forward reaction and reverse reaction to the same extent

(d)

Equilibrium constant varied with temperature

7. K1 and K2 are the equilibrium constants for the reactions respectively.
${ N }_{ 2 }(g)+{ O }_{ 2 }(g)\overset { { K }_{ 1 } }{ \rightleftharpoons } 2NO(g)$
$2NO(g)+{ O }_{ 2 }(g)\overset { { K }_{ 2 } }{ \rightleftharpoons } { 2NO }_{ 2 }(g)$
What is the equilibrium constant for the reaction NO2(g) ⇌ ½N2(g) + O2(g)

(a)

${1\over \sqrt{K_1K_2}}$

(b)

(K1 = K2)1/2

(c)

${1\over 2K_1K_2}$

(d)

$({1\over K_1K_2})^{3/2}$

8. In the equilibrium,
2A(g) ⇌ 2B(g) + C2(g)
the equilibrium concentrations of A, B and C2 at 400 K are 1 × 10–4 M, 2.0 × 10–3 M, 1.5 × 10–4 M respectively. The value of KC for the equilibrium at 400 K is

(a)

0.06

(b)

0.09

(c)

0.62

(d)

3 x 10-2

9. An equilibrium constant of 3.2 × 10–6 for a reaction means, the equilibrium is

(a)

largely towards forward direction

(b)

largely towards reverse direction

(c)

never established

(d)

none of these

10. ${K_c\over K_p}$ for the reaction,
N2(g) + 3H2(g) ⇌ 2NH3(g) is

(a)

${1\over RT}$

(b)

$\sqrt{RT}$

(c)

RT

(d)

(RT)2

11. For the reaction AB (g) ⇌ A(g) + B(g), at equilibrium, AB is 20% dissociated at a total pressure of P, The equilibrium constant KP is related to the total pressure by the expression

(a)

P = 24 KP

(b)

P = 8 KP

(c)

24 P = KP

(d)

none of these

12. In which of the following equilibrium, KP and KC are not equal?

(a)

2 NO(g) ⇌ N2(g) + O2(g)

(b)

SO2 (g) + NO2 ⇌ SO3(g) + NO(g)

(c)

H2(g) + I2(g) ⇌ 2HI(g)

(d)

PCl5 (g) ⇌ PCl3(g) + Cl2(g)

13. If x is the fraction of PCl5 dissociated at equilibrium in the reaction
PCl5 ⇌ PCl3 + Cl2
then starting with 0.5 mole of PCl5, the total number of moles of reactants and products at equilibrium is

(a)

0.5 - x

(b)

x + 0.5

(c)

2x + 0.5

(d)

x + 1

14. The values of KP1 and KP2 for the reactions
X ⇌ Y + Z
A ⇌ 2B are in the ratio 9: 1 if degree of dissociation and initial concentration of X and A be equal then total pressure at equilibrium P1 and P2 are in the ratio

(a)

36: 1

(b)

1: 1

(c)

3: 1

(d)

1: 9

15. In the reaction,
Fe (OH)3 (s) ⇌ Fe3+(aq) + 3OH(aq),
if the concentration of OH ions is decreased by ¼ times, then the equilibrium concentration of Fe3+ will

(a)

not changed

(b)

also decreased by ¼ times

(c)

increase by 4 times

(d)

increase by 64 times

16. Consider the reaction where KP = 0.5 at a particular temperature
PCl5(g) ⇌ PCl3 (g) + Cl2 (g)
if the three gases are mixed in a container so that the partial pressure of each gas is initially 1 atm, then which one of the following is true

(a)

more PCl3 will be produced

(b)

more Cl2 will be produced

(c)

more PCl5 will be produced

(d)

none of these

17. Equimolar concentrations of H2 and I2 are heated to equilibrium in a 1 litre flask. What percentage of initial concentration of Hhas reacted at equilibrium if rate constant for both forward and reverse reactions are equal

(a)

33%

(b)

66%

(c)

(33)2%

(d)

16.5%

18. In a chemical equilibrium, the rate constant for the forward reaction is 2.5 × 102 and the equilibrium constant is 50. The rate constant for the reverse reaction is,

(a)

11.5

(b)

5

(c)

2 x 102

(d)

2 x 10-3

19. Which of the following is not a general characteristic of equilibrium involving physical process

(a)

Equilibrium is possible only in a closed system at a given temperature

(b)

The opposing processes occur at the same rate and there is a dynamic but stable condition

(c)

All the physical processes stop at equilibrium

(d)

All measurable properties of the system remains constant

20. For the formation of Two moles of SO3(g) from SO2 and O2, the equilibrium constant is K1. The equilibrium constant for the dissociation of one mole of SO3 into SO2 and O2 is

(a)

$1/K_1$

(b)

$K_1^2$

(c)

$({1\over K_1})^{1/2}$

(d)

${K_1\over 2}$

21. Match the equilibria with the corresponding conditions,

 i) Liquid ⇌ Vapour 1) melting point ii) Solid ⇌ Liquid 2) Saturated solution iii) Solid ⇌ Vapour 3) Boiling point iv) Solute (s) ⇌ Solute (Solution) 4) Sublimation point 5) Unsaturated solution
(a)
 (i) (ii) (iii) (iv) 1 2 3 4
(b)
 (i) (ii) (iii) (iv) 3 1 4 2
(c)
 (i) (ii) (iii) (iv) 2 1 3 4
(d)
 (i) (ii) (iii) (iv) 3 2 4 5
22. Consider the following reversible reaction at equilibrium, A + B ⇌ C, If the concentration of the reactants A and B are doubled, then the equilibrium constant will

(a)

be doubled

(b)

become one fourth

(c)

be halved

(d)

remain the same

23. [Co(H2O)6]2+ (aq) (pink) + 4Cl (aq) ⇌ [CoCl4]2– (aq) (blue)+ 6 H2O (l)
In the above reaction at equilibrium, the reaction mixture is blue in colour at room temperature. On cooling this mixture, it becomes pink in colour. On the basis of this information, which one of the following is true?

(a)

ΔH > 0 for the forward reaction

(b)

ΔH = 0 for the reverse reaction

(c)

ΔH < 0 for the forward reaction

(d)

Sign of the ΔH cannot be predicted based on this information

24. The equilibrium constants of the following reactions are:

 N2 + 3H2 ⇌ 2NH3   : K1 N2 + O2 ⇌ 2NO      : K2 H2 + ½O2 ⇌ H2O   : K3

The equilibrium constant (K) for the reaction ;
${ 2NH }_{ 3 }+5/2{ O }_{ 2 }\overset { K }{ \rightleftharpoons } 2NO+{ 3H }_{ 2 }{ O },$ will be

(a)

$K_2^3{K_3\over K_1}$

(b)

$K_1{K_3^3\over K_2}$

(c)

$K_2{K_3^3\over K_1}$

(d)

$K_2{K_3\over K_1}$

25. A 20 litre container at 400 K contains CO2 (g) at pressure 0.4 atm and an excess of SrO (neglect the volume of solid SrO). The volume of the container is now decreased by moving the movable piston fitted in the container. The maximum volume of the container, when pressure of CO2 attains its maximum value will be:
Given that: SrCO3 (S) ⇌ SrO (S) + CO2(g)
KP = 1.6 atm

(a)

2 litre

(b)

5 litre

(c)

10 litre

(d)

4 litre

26. PART -B

15 x 2 = 30
27. Consider the following equilibrium reactions
and relate their equilibrium, constants
i) N2 + O2 ⇌ 2NO ; K1
ii) 2NO + O2 ⇌ 2NO2 ; K2
iii) N2 + 2O2 ⇌ 2NO2 ; K3

28. If there is no change in concentration, why is the equilibrium state considered dynamic?

29. For a given reaction at a particular temperature, the equilibrium constant has constant value. Is the value of Q also constant? Explain.

30. What the relation between KP and KC. Give one example for which KP is equal to KC.

31. For a gaseous homogeneous reaction at equilibrium, number of moles of products are greater than the number of moles of reactants. Is KC is larger or smaller than KP.

32. When the numerical value of the reaction quotient (Q) is greater than the equilibrium constant (K), in which direction does the reaction proceed to reach equilibrium?

33. State Le-Chatelier principle.

34. Consider the following reactions,
a) H2(g) + I2(g) ⇌ 2 HI
b) CaCO3 (s) ⇌ CaO (s) + CO2(g)
c) S(s) + 3F2 (g) ⇌ SF6 (g)
In each of the above reaction find out whether you have to increase (or) decrease the volume to increase the yield of the product.

35. State law of mass action.

36. Explain how will you predict the direction of a equilibrium reaction.

37. Derive a general expression for the equilibrium constant KP and KC for the reaction 3H2(g) + N2(g) ⇌ 2NH3(g).

38. Write a balanced chemical equation for a equilibrium reaction for which the equilibrium constant is given by expression
$K_c={[NH_3]^4[O_2]^5\over [NO]^4[H_2O]^6}$

39. What is the effect of added inert gas on the reaction at equilibrium.

40. Derive the relation between KP and KC.

41. Deduce the Vant Hoff equation.

42. PART- C

10 x 3 = 30
43. The value of Kc for the following reaction at 717 K is 48.

44. The value of Kc for the reaction

45. One mole of H2 and one mole of I2 are allowed to attain equilibrium. If the equilibrium mixture contains 0.4 mole of HI. Calculate the equilibrium constant.

46. The equilibrium concentrations of NH3, N2 and H2 are 1.8 × 10-2 M, 1.2 × 10-2 M and 3 × 10-2 M respectively. Calculate the equilibrium constant for the formation of NH3 from N2 and H2. [Hint: M= mol lit-1]

47. For an equilibrium reaction Kp = 0.0260 at 25° C ΔH= 32.4 kJmol-1, calculate Kp at 37° C

48. For the reaction,
A2(g) + B2(g) ⇌ 2AB(g) ; ΔH is –ve.
the following molecular scenes represent different reaction mixture (A – green, B – blue)

i) Calculate the equilibrium constant KP and (KC).
ii) For the reaction mixture represented by scene (x), (y) the reaction proceed in which directions?
iii) What is the effect of increase in pressure for the mixture at equilibrium.

49. One mole of PCl5 is heated in one litre closed container. If 0.6 mole of chlorine is found at equilibrium, calculate the value of equilibrium constant.

50. For the reaction
SrCO3 (s) ⇌ SrO (s) + CO2(g),
the value of equilibrium constant KP = 2.2 × 10–4 at 1002 K. Calculate KC for the reaction.

51. To study the decomposition of hydrogen iodide, a student fills an evacuated 3 litre flask with 0.3 mol of HI gas and allows the reaction to proceed at 500o C. At equilibrium he found the concentration of HI which is equal to 0.05 M. Calculate KC and KP.

52. Oxidation of nitrogen monoxide was studied at 200o C with initial pressures of 1 atm NO and 1 atm of O2. At equilibrium partial pressure of oxygen is found to be 0.52 atm calculate KP value.

53. PART- D

13 x 5 = 65
54. The equilibrium constant at 298 K for a reaction is 100.
A + B $\rightleftharpoons$ C + D
If the initial concentration of all the four species is 1 M, the equilibrium concentration of D (in mol lit-1) will be

55. Consider the following reaction
Fe3+(aq) + SCN(aq) ⇌ [Fe(SCN)]2+(aq)
A solution is made with initial Fe3+, SCN- concentration of 1 x 10-3 M and 8 x 10-4 M respectively. At equilibrium [Fe(SCN)]2+ concentration is 2 x 10-4 M. Calculate the value of equilibrium constant.

56. The atmospheric oxidation of NO
2NO(g) + O2(g) ⇌ 2NO2(g)
was studied with initial pressure of 1 atm of NO and 1 atm of O2. At equilibrium, partial pressure of oxygen is 0.52 atm calculate Kp of the reaction.

57. The following water gas shift reaction is an important industrial process for the production of hydrogen gas.
CO(g) + H2O(g) ⇌ CO2(g) + H2(g)
At a given temperature Kp = 2.7. If 0.13 mol of CO, 0.56 mol of water, 0.78 mol of CO2 and 0.28 mol of H2 are introduced into a 2 L flask, and find out in which direction must the reaction proceed to reach equilibrium

58. 1 mol of PCl5, kept in a closed container of volume 1 dm3 and was allowed to attain equilibrium at 423 K. Calculate the equilibrium composition of reaction mixture. (The Kc value for PCl5 dissociation at 423 K is 2)

59. The equilibrium constant for the following reaction is 0.15 at 298 K and 1 atm pressure.
N2O4(g) ⇌ 2NO2(g);
ΔHº = 57.32 KJmol-1
The reaction conditions are altered as follows.
a) The reaction temperature is altered to 100o C keeping the pressure at 1 atm, Calculate the equilibrium constant.

60. 1 mol of CH4, 1 mole of CS2 and 2 mol of H2S are 2 mol of H2 are mixed in a 500 ml flask. The equilibrium constant for the reaction KC = 4 × 10–2 mol2 lit–2. In which direction will the reaction proceed to reach equilibrium?

61. At particular temperature KC = 4 × 10–2 for the reaction
H2S(g) ⇌ H2(g) + ½ S2(g)
Calculate KC for each of the following reaction
i) 2H2S (g) ⇌ 2H2 (g) + S2 (g)
ii) 3H2S (g) ⇌ 3H2 (g) + 3/2 S2(g)

62. 28 g of Nitrogen and 6 g of hydrogen were mixed in a 1 litre closed container. At equilibrium 17 g NH3 was produced. Calculate the weight of nitrogen, hydrogen at equilibrium.

63. The equilibrium for the dissociation of XY2 is given as,
2XY2 (g) ⇌ 2XY (g) + Y2(g)
if the degree of dissociation x is so small compared to one. Show that 2 KP = PX3 where P is the total pressure and KP is the dissociation equilibrium constant of XY2.

64. A sealed container was filled with 1 mol of A2 (g), 1 mol B2 (g) at 800 K and total pressure 1.00 bar. Calculate the amounts of the components in the mixture at equilibrium given that K = 1 for the reaction
A2 (g) + B2 (g) ⇌ 2AB (g)

65. The equilibrium constant KP for the reaction
N2(g) + 3H2(g) ⇌ 2NH3(g) is 8.19 × 102 at 298 K and 4.6 × 10–1 at 498 K. Calculate ΔHo for the reaction

66. The partial pressure of carbon dioxide in the reaction
CaCO3 (s) ⇌ CaO (s) + CO2(g) is 1.017 × 10–3 atm at 5000 C. Calculate KP at 6000c C for the reaction. ΔH for the reaction is 181 KJ mol–1 and does not change in the given range of temperature.