Classes at: - Topic: Chemical Equilibrium

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1 PHYSICAL CHEMISTRY by: SHAILENDRA KR. Classes at: - SCIENCE TUTORIALS; Opp. Khuda Baksh Library, Ashok Rajpath, Patna PIN POINT STUDY CIRCLE; House No. 5A/65, Opp. Mahual Kothi, Alpana Market, Patna Topic: Chemical Equilibrium Meq. Approach 01. mole of PCl 5 were heated in a closed vessel of litre capacity. At equilibrium 40% of PCl 5 dissociated into PCl 3 and Cl. The value of equilibrium constant is: (a) 0.67 (b) 0.53 (c).63 (d) One mole of ethyl alcohol was treated with one mole of acetic acid at 5 C. /3 of the acid changes into ester at equilibrium. The equilibrium constant for the reaction will be : (a) 1 (b) (c) 3 (d) If in the reaction NO, α is degree of dissociation of then the number of molecules at equilibrium will be: (a) 3 (b) 1 (c) (1 α) (d) (1+α) 04. If CuS 5H O CuS 3H O(s) + H O (v) K p = atm at 5 C. The efflorescent nature of CuS 5H O can be noticed when vapour pressure of H O in atmosphere is: (a) > 7.9 mm (b) < 7.9 mm (c) >< 7.9 mm (d) None of these 05. Sulphide ions in alkaline solution react with solid sulphur to form polyvalent sulphide ions. The equilibrium constant for the formation of S and S 3 from S and S ions are 1.7 and 5.3 respectively. Equilibrium constant for the formation of S 3 from S and S is: (a) 1.33 (b) 3.11 (c) 4.1 (d) When 0 g of CaCO 3 were put into 10 litre flask and heated to 800 C, 35% of CaCO 3 remained unreacted at equilibrium. K p for decomposition of CaCO 3 is: (a) atm (b) atm (c).145 atm (d) atm mole of A are mixed with. mole of B and the mixture is then kept in one litre flask till the equilibrium is attained A + B C + D. At the equilibrium, 0. mole of C are formed. The equilibrium constant of the reaction is: (a) (b) 0.00 (c) (d) In a chemical equilibrium, the rate constants of the forward and backward reactions are respectively and , the equilibrium constant is: (a) 0.37 (b) 6.7 (c) 0.5 (d) For the reaction, NO NO + O, K c = at 185 C. At 185 C, the K c for NO + 1/ O NO is : (a) (b) (c) (d) mole of A are mixed with 4 mole of B, when mole of C are formed at equilibrium, according to the reaction, A + B C + D. The equilibrium constant is: Page No.: 1

2 (a) 4 (b) 1 (c) (d) For the reaction, H + I HI at 70 K, the value of equilibrium constant is 50, when equilibrium concentration of both H and I is 0.5 M.K p under the same conditions will be: (a) 0.0 (b) 0. (c) 50 (d) 50RT 1. At a given temperature, the K c for the reaction, PCl 5 PCl 3 + Cl is At the same temperature, The K c for the reaction PCl 3 + Cl PCl 5 is : (a) (b) (c) (d) On adding A to the reaction at equilibrium, AB (s) A + B, the new equilibrium concentration of A becomes double, the equilibrium concentration of B would become: (a) 1/ of its original value (b) 1/4 of its original value (c) 1/8 of its original value (d) Twice its original value 14. For a reaction, A + B C, where initial concentration of A = M, B = 1M and C = 0, the concentration of B at equilibrium is 0.5 M. The value of equilibrium constant for the reaction is: (a) 0.5 (b).0 (c) 1.0 (d) For a reaction + 3H NH 3 ; H = kcal. If energy of activation for this reaction is 70 kcal, the energy of activation for backward reaction is : (a) 70 kcal (b) 9 kcal (c) 48 kcal (d) none of these 16. The equilibrium constant for the reaction; P 4 (s) + 5O P 4 O 10 (s) is : 1 (a) K c = (b) K c = [O [O 5 5 [P 4 O 10 [P (c) K c = 4 O 10 (d) K c = 5[P 4 [O [P 4 [O Equilibrium is established in the reaction, A (aq.) + B (aq.) C (aq.) If equilibrium concentration are [A = 0.5, [B = 0.4 and [C = 0.5 mol dm 3. The value of K c is: (a) 0.5 (b) 0.4 (c).5 (d) At a certain temperature, HI H + I only 50% HI is dissociated at equilibrium. The equilibrium constant is: (a) 1.0 (b) 3.0 (c) 0.5 (d) The reaction, A + B C + D was studied using an initial concentration of B which was 1.5 more that of A. But the equilibrium concentration of A and C were found to be equal. Then the K c for the equilibrium is : (a) 4 (b) 8 (c) 6 (d) In a system : A (s) B + 3C. If the concentration of C at equilibrium is increased by a factor, it will cause the equilibrium concentration of B to change to: (a) two times of its original value (b) one half of its original value (c) times of its original value (d) 1/ times of its original value 1. The vapour density of undecomposed is 46. When heated, vapour density decreases to 4.5 due to its dissociation to NO. The percent dissociation of at the final temperature is : (a) 87 (b) 60 (c) 40 (d) 70. For an equilibrium change involving gaseous phase, the forward reaction is first order while the reverse reaction is second order. The unit of K p for the forward equilibrium is : Page No.:

3 (a) Atm (b) Atm (c) Atm 1 (d) Atm 3. The formation of phosgene is represented as, CO + Cl COCl The reaction is carried out in 500 ml flask. At equilibrium 0.3 mole of phosgene, 0.1 mole of CO and 0.1 mole of Cl are present. The equilibrium constant of the reaction is: (a) 30 (b) 15 (c) 5 (d) 3 4. Gº for the reaction X + Y Z is kcal. The equilibrium constant for the reaction at 7 C is: (a) 100 (b) 10 (c) (d) The partial pressure of CH 3 OH, CO and H in equilibrium mixture for the reaction, CO + H CH 3 OH are.0, 1.0 and 0.1 atm respectively at 47ºC. The value of K p for the decomposition of CH 3 OH to CO and H is : (a) 10 atm (b) 10 atm 1 (c) 50 atm (d) atm 6. The equilibrium constant of a reaction is 0.0. At equilibrium, the rate constant of forward reaction is The rate constant for backward reaction is: (a) 0.5 (b).0 (c) 10.0 (d) For the reaction, C(s) + CO CO, the partial pressures of CO and CO are.0 and 4.0 atm respectively at equilibrium. The K p for the reaction is: (a) 0.5 (b) 4.0 (c) 8.0 (d) In the reaction, PCl 3 PCl 3 + Cl, the amounts of PCl 5, PCl 3 and Cl at equilibrium are mole each and the total pressure is 3 atm. The equilibrium constant K p is : (a) 1.0 atm (b).0 atm (c) 3.0 atm (d) 6.0 atm 9. In an aqueous solution of volume 500 ml, when the reaction of Ag + +Cu Cu + + Ag reached equilibrium the [Cu + was x M. When 500 ml of water is further added, at the equilibrium [Cu + will be: (a) x M (b) x M (c) Between x M and x/ M (d) Less than x/ M % of a mixture of 0. mole of and 0.6 mole of H react to give NH 3 according to the equation, + 3H NH 3 at constant temperature and pressure. Then the ratio of the final volume to the initial volume of gases are: (a) 4 : 5 (b) 5 : 4 (c) 7 : 10 (d) 8 : At temperature T, a compound AB dissociates according to the reaction AB AB + B with a degree of dissociation x, which is small compared with unity. The expression for K p, in terms of x and the total pressure P, is: (a) Px 3 / (b) Px / 3 (c) Px 3 / 3 (d) Px / 3. Two systems PCl 5 PCl 3 + Cl and COCl CO + Cl are simultaneously in equilibrium in a vessel at constant volume. If some CO is introduced into the vessel then at the new equilibrium the concentration of : (a) PCl 5 is greater (b) PCl 3 remains unchanged (c) PCl 5 is less (d) Cl is greater 33. K c for the reaction: [Ag(CN) Ag + + CN, the equilibrium constant at 5ºC is , then the silver ion concentration in a solution which was originally 0.1 molar in KCN and 0.03 molar in AgNO 3 is: (a) (b) (c) (d) Page No.: 3

4 34. For the reaction A + B 3C at 5ºC, a 3 litre vessel contains 1,, 4 mole of A, B and C respectively. If K c for the reaction is 10, the reaction will proceed in: (a) Forward reaction (b) Backward reaction (c) In either direction (d) In equilibrium 35. The equilibrium constant K c for A B is 1.1, Gas B will have molar concentration greater than 1 if: (a) (A) = 0.91 (b) (B) > 0.91 (c) (A) > 1 (d) At all these 36. Amount of PCl 5 (in mole) need to be added to one litre vessel at 50ºC in order to obtain a concentration of 0.1 mole of Cl for the given change is: PCl 5 PCl 3 + Cl ; K c = mol/litre (a) (b) (c) (d) For the reaction, CO + Cl COCl the value of K p /K c is equal to: (a) 1.0 (b) RT (c) RT (d) 1/RT 38. The equilibrium constant (K c ) for the reaction, + O NO at room temperature T is The value of K c for NO 1/ + 1/ O at the same T is: (a) 0.0 (b) 50 (c) (d) A definite amount of solid NH 4 HS is placed in a flask already containing NH 3 gas at certain temperature and 0.50 atm pressure. NH 4 HS decomposes to give NH 3 and H S and total equilibrium pressure in flask is 0.84 atm. The equilibrium constant for the reaction is: (a) 0.30 (b) 0.18 (c) 0.17 (d) The equilibrium constant for the reaction, SO 3 SO + 1/ O is K c = The value of K c for the reaction SO + O SO 3 will be (a) 416 (b) (c) (d) For an endothermic reaction where H represent the enthalpy of the reaction in kj/ mol, the minimum value for energy of activation will be: (a) Less than H (b) Zero (c) More than H (d) Equal to H 4. Favourable conditions for manufacture of ammonia by the reaction, + 3H NH 3 ; H = 1.9 kcal are: (a) Low temperature, low pressure and catalyst (b) Low temperature, high pressure and catalyst (c) High temperature, low pressure and catalyst (d) High temperature, high pressure and catalyst 43. Predict the conditions for forward reaction on the basis of Le-Chatelier s principle for: SO + O SO 3 H = 198 kj (a) Lowering the temperature and increasing pressure (b) Any value of temperature and pressure (c) Lowering of temperature as well as pressure (d) Increasing temperature as well as pressure 44. The reaction quotient (Q) at equilibrium is : (a) = 1 (b) = K (c) > K (d) < K 45. A chemical reaction A B is said to be at equilibrium when: (a) Complete conversion of A to B has taken place Page No.: 4

5 (b) Conversion of A to B is only 50% complete (c) Only 10% conversion of A to B has taken place (d) The rate of transformation of A to B is just equal to the rate of transformation of B to A in the system 46. For + 3H NH 3 ; H = ve then: (a) K p (b) K p RT (RT) (d) K p (RT) On applying pressure to the equilibrium, Ice water Which phenomenon will happen? (a) More ice will be formed (b) More water will be formed (c) Equilibrium will not be disturbed (d) Water will evaporate 48. Oxidation of SO by O to SO 3 is an exothermic reaction. The yield of SO 3 will be maximum if: (a) Temperature is increased and pressure is kept constant (b) Temperature is reduced and pressure is increased (c) Both temperature and pressure are increased (d) Both temperature and pressure are reduced 49. The equilibrium constant Br Br at 500 K and 700 K are and 10 5 respectively. The reaction is: (a) Endothermic (b) Exothermic (c) Fast (d) Slow 50. Which equilibrium in gaseous phase would be unaffected by an increase in pressure? (a) NO (b) + O NO (c) + 3H NH 3 (d) CO + 1/ O CO 51. For the reaction H + I HI: (a) K c = K p (b) K c > K p (c) K c = K p (d) K c < K p 5. For the chemical reaction, 3X + Y X 3 Y ; the amount of X 3 Y at equilibrium is affected by: (a) Temperature and pressure (b) Temperature only (c) Pressure only (d) Temperature, pressure and catalyst 53. Which oxide of nitrogen is the most stable? (a) NO + O ; K = mol litre 1 (b) NO + O ; K = mol litre 1 (c) O 5 + 5O ; K = mol 5 litre 5 (d) O + O ; K = mol litre A higher value for equilibrium constant, K shows that: (a) The reaction has gone to near completion towards right (b) The reaction has not yet started (c) The reaction has gone to near completion toward left (d) None of the above 55. If K 1 and K are equilibrium constants for reaction (I) and (II) respectively for, + O NO...(I) 1/ + 1/ O NO...(II) Then: (a) K = K 1 (b) K = K 1 (c) K 1 = K (d) K 1 = 1/ K 56. If pressure is applied to the equilibrium of solid liquid. The melting point of the solid: (a) Will not change (b) May increase or decrease depending upon its nature (c) Will always increase (d) Will always decrease Page No.: 5

6 57. For the reaction equilibrium, NOBr NO + Br, If P Br = P/9 at equilibrium and P is total pressure. The ratio K p /P is equal to: (a) 1/9 (b) 1/81 (c) 1/7 (d) 1/3 58. In lime kiln, the reversible reaction, CaCO 3 (s) CaO (s) + CO proceeds to completion because : (a) of high temperature (b) CO escapes out (c) CaO is removed (d) of low temperature 59. When two reactants A and B are mixed to give products C and D, the reaction quotient Q, at the initial stages of the reaction: (a) Is zero (b) Decrease with time (c) Is independent of time (d) Increases with time 60. For the reaction, CuS 5H O(s) CuS 3H O(s) + H O(v) Which one is correct representation? (a) K p = (p H O ) (b) K c = [H O (RT) (d) All of these 61. The equilibrium constant for the reactions are: k 1 H 3 P H + + H P ; K 1 k H P H + + HP ; K k 3 HP H P ; K 3 The equilibrium constant for N 3 P 3H P will be: (a) K 1 /K K 3 (b) K 1 K K 3 (c) K /K 1 K 3 (d) K 1 + K + K 3 6. In which of the following equilibrium, change in volume of the system does not alter the number of moles? (a) + O NO (b) PCl 5 PCl 3 + Cl (c) + 3H NH 3 (d) SOCl SO + Cl 63. In an equilibrium reaction, if G = 0 the equilibrium constant, K should be equal to: (a) 0 (b) 1 (c) (d) For a system in equilibrium, G = 0 under conditions of constant: (a) temperature and pressure (b) temperature and volume (c) Energy and volume (d) Pressure and volume 65. Raising the temperature of a reversible chemical reaction: (a) Favours the forward rate only (b) Favours the backward rate only (c) Favours both the forward and backward rates as the case may be (d) Favours neither the forward not backward rates 66. For reaction PCL 3 + Cl PCl 5, the value of K c at 50ºC is 6 mol litre 1. The value of K p at this temperature will be: (a) 0.61 atm 1 (b) 0.57 atm 1 (c) 0.83 atm 1 (d) 0.46 atm In which of the following cases, does the reaction go furthest to completion? (a) K = 10 3 (b) K = 10 (c) K = 10 (d) K =1 68. If K 1 and K are the respective equilibrium constants for the two reactions, XeF 6 + H O XeOF 4 + HF Xe + XeF 6 XeOF 4 + XeO 3 F The equilibrium constant for the reaction, Xe + HF XeO 3 F + H O is: (a) K 1 K (b) K 1 /K (c) K /K 1 (d) K 1 /K Page No.: 6

7 69. If 1.0 mole of I is introduced into 1.0 litre flask at 1000 K, at equilibrium (K c = 10 6 ), which one is correct? (a) [I > [I ) (b) [I < [I (c) [I = [I (d) [I = 1/[I 70. For the reactions, A B; K c = B C; K c = 4 C D; K c = 6 K c for the reaction, A D is: (a) ( ) (b) ( 4)/6 (c) (4 6)/ (d) For a reaction in equilibrium: (a) There is no volume change (b) The reaction has stopped completely (c) The rate of forward reaction is equal to the rate of backward reaction (d) The forward reaction is faster than reverse reaction 7. In a flask colourless is in equilibrium with brown coloured NO. At equilibrium, when the flask is heated at 100ºC the brown colour deepens and on cooling it becomes less coloured. The change in enthalpy H, for the system is: (a) Negative (b) Positive (c) Zero (d) Undefined 73. Increase in temperature favours the forward reaction in: (a) SO + O SO 3 (b) O 3 3O (c) C (graphite) C (diamond) (d) H + 1/ O H O 74. An example of reversible reaction is: (a) AgNO 3 (aq) + HCl(aq) AgCl(s) + HNO 3 (aq) (b) Na + H O NaOH + H (c) NaOH + CH 3 COOH CH 3 COONa + H O (d) Pb(NO 3 ) + NaI PbI + NaNO The equilibrium constant for the reactions, + O NO, NO + 1/ O NO are K 1 and K respectively. Then the equilibrium constant for the equilibrium + O NO is: (a) K 1 / K (b) K 1 K (c) K 1 K (d) K 1 K 76. K p / K c for the reaction, CO + 1/ O CO is: (a) RT (b) 1/ RT (c) RT (d) Consider the following equilibrium in a closed container: NO At a fixed temperature, the volume of the reaction container is halved. For this change, which of the give statements holds true regarding the equilibrium constant (K p ) and degree of dissociation (α)? (a) Neither K p nor α change (b) Both K p and α change Changes, but α does not changes (d) K p does not changes, but α changes 78. At constant temperature, the equilibrium constant (K p ) for the decomposition reaction. NO is expressed by, K p = (4x P) (1 x ) Where P = pressure, x = extend of decomposition. Which of the following statement is true? (a) K p increases with increase of P (b) K p increases with increase of x increases with decrease of x (d) K p remains constant with change in P or x 79. In which of the following reaction increase in pressure at constant temperature does not affect the moles at equilibrium? Page No.: 7

8 (a) NH 3 + 3H (b) C + 1/ O CO (c) H + 1/ O H O (d) H + I HI 80. For the reaction: CO + 1/ O CO, K p / K c is: (a) RT (b) (RT) 1 (c) (RT) 1/ (d) (RT) 1/ 81. The exothermic formation of ClF 3 is represented by the equation: Cl + 3F ClF 3 ; H = 39 kj Which of the following will increase the quantity of ClF 3 in equilibrium mixture of Cl, F and ClF 3? (a) Increasing the temperature (b) Removing Cl (c) Increasing the volume of container (d) Adding F 8. For the reaction : NO NO + O ; K c = at 184ºC and R = JK 1 mol 1. When K p and K c are compared at 184ºC. It is found that: (a) K p > K c (b) K p < K c (d) K p <> K c 83. The graph relates In K eq vs (1/T) for a reaction. The reaction must be: (a) exothermic InK eq (b) Endothermic (c) H is negligible (d) Highly spontaneous at ordinary temperature 84. When two reactants A and 1/T B are mixed to give products C and D, the reaction quotient, Q at the initial stages of reaction: (a) is zero (b) decreases with time (c) independent of time (d) increases with time 85. Equilibrium constants K 1 and K for the following equilibria are related as: NO + 1/ O NO ; K 1 NO NO + O ; K 1 (a) K = (b) K = K 1 1 K 1 K (c) K = K 1 (d) K = For the reaction, CH 4 + O CO + H O(l), r H = kj mol 1 Which of the following statements is not true? (a) Addition of CH 4 or O at equilibrium will cause to the right (b) The reaction is exothermic (c) At equilibrium, the concentrations of CO and H O (l) are not equal (d) the equilibrium constant for the reaction is give by [CO K p = [CH 4 [ O 87. Phosphorus pentachloride dissociates as follows, in a closed reaction vessel, PCl 5 PCl 3 + Cl If total pressure at equilibrium of the reaction mixture is P and degree of dissociation of PCl 5 is x, the partial pressure of PCl 3 will be: x x (a) P (b) P x x x x (c) P (d) P x 1 1 x Page No.: 8

9 A n s w e r s 01. a 0. d 03. d 04. b 05. b 06. a 07. a 08. b 09. b 10. b 11. c 1. c 13. a 14. c 15. b 16. a 17. c 18. d 19. d 0. d 1. a. a 3. b 4. a 5. d 6. a 7. c 8. a 9. d 30. a 31. a 3. c 33. b 34. b 35. d 36. a 37. d 38. b 39. d 40. a 41. c 4. b 43. a 44. b 45. d 46. c 47. b 48. b 49. a 50. b 51. c 5. a 53. a 54. a 55. b 56. b 57. b 58. b 59. a 60. d 61. b 6. a 63. b 64. a 65. c 66. a 67. a 68. c 69. a 70. d 71. c 7. b 73. c 74. c 75. c 76. b 77. d 78. d 79. d 80. c 81. d 8. a 83. a 84. d 85. a 86. d 87. a Page No.: 9