Chemical Equilibrium MCQs – 1
1) For the gaseous equilibrium, H2 + X2 + heat 2HX, the formation of HX is favoured by
a) High pressure and low temperature
b) High temperature
c) Low temperature and high pressure
d) High temperature and low pressure
2) Which favours the backward reaction in a chemical equilibrium ?
a) Increasing the concentration of one of the reactants
b) Removal of at least one of the products at regular intervals
c) Increasing the concentration of one or more of the products
d) All of these
3) When any system in equilibrium is subjected to a change in pressure, concentration or temperature, the equilibrium is shifted in the direction which tends to undo the effect of the change. This is called
a) First law of thermodynamics
4) All reactions involving chemical decomposition are
b) Reversible and endothermic
d) May be either reversible or irreversible and either endothermic or exothermic
5) A cylinder filled with a movable piston contains liquid water in equilibrium with water vapour at 25Â°C. Which of the following results in a decrease in the equilibrium vapour pressure ?
a) Moving the piston downward at short distance
b) Removing a small amount of vapour
c) Removing a small amount of liquid water
d) Dissolving salt in water
6) The solubility of CO2 in water increases with
a) an increase in temperature
b) An increase in pressure
c) A decrease in pressure
7) For PCl5(g) PCl3(g) + Cl2(g); D H = 22 k.cals, the dissociation of PCl5 will be more on
a) Increasing the temperature
b) Decreasing the temperature
c) Increasing the pressure
d) Increasing the concentration of chlorine
8) An increase in the temperature of the reaction N2 + O2 2NO; D H= 43.2 k.cals will
a) Increase the yield of NO
b) Decrease the yield of NO
c) Not affect the yield of NO
d) Not help the reaction to proceed in the forward direction
9) The volume of the reaction vessel containing an equilibrium mixture of the reaction SO2Cl2(g) SO2(g) + Cl2(g) is increased. When equilibrium is reestablished
10) Increase in temperature favours the forward reaction in
11) Just before a reversible reaction attains equilibrium it is found that
a) The rate of both the forward reaction and the backward reaction is increasing
b) The rate of the forward reaction is decreasing and that of the backward reaction is increasing
c) The rate of both the forward and backward reactions is increasing
12) Consider the reversible reaction HCN (aq) H+ (aq) + CN– (aq). At equilibrium the addition of CN– (aq) would
a) Reduce HCN (aq) concentration
c) Increase the equilibrium constant
d) Decrease the equilibrium constant
13) In which of the following is Kp less than Kc ?
14) For the equilibrium 2NO2 (g) N2O4(g) + 14.6 k.cals, an increase of temperature could
c) Not affect the equilibrium
d) Stop the reaction
15) @ If in the reaction N2O4 2NO2, a is that part of N2O4 which dissociates, then the number of molecules at equilibrium will be
16) For the endothermic reaction N2(g) + O2(g) 2NO(g) which of the following is true?
a) K is independent of temperature
b) K increases as temperature increases
c) K decreases as temperature decreases
d) K varies with the addition of NO
17) Which of the following changes will invariably increase the yield of products at equilibrium?
a) An increase in T
b) An increase in P
c) Addition of a catalyst
d) Increasing the original reactant concentration
18) A reversible reaction H2 + Cl2 2HCl is carried out in a one litre flask. If the same reaction is carried out in a two litre flask, the equilibrium constant will be
d) remain the same
19) In the Ostwald Process, 4NH3 + 5O2 4NO + 6H2O, platinum is used as a catalyst. If the amount of catalyst is increased when the system has reached equilibrium, which of the following will occur ?
c) The reaction rate will be increased
d) No change will be evident
20) The equilibrium constant of the reaction A + BC +D is 10. If the rate constant of the forward reaction is 203, the rate constant of the backward reaction is
21) Pure NH3 is placed in a vessel at a temperature where its dissociation constant is appreciable. If the pressure is changed, the
b) Concentration of hydrogen is less than that of nitrogen at high pressure
c) Concentration of ammonia does not change with pressure
d) amount of ammonia that dissociates at higher pressure is less
22) At equilibrium, the amount of HI in a 3 litre vessel was 12.8 g. Its equilibrium concentration is
a) 4.267 M
b) 0.033 M
23) For the reaction CO(g) + 2H2(g) CH3OH(g)
24) @ For the reaction C (s) + CO2(g) 2CO, the (g) equilibrium mixture has a partial pressure of 4.0 and 8.0 atm.for CO2 and CO respectively. Kp for the reaction is
25) @ The equilibrium constant for H2(g) + CO2(g) H2O(g) + CO(g) is 1.80 at 1000Â°C. If 1.0 mole of H2 and 1.0 mole of CO2 are placed in a one litre flask, the final equilibrium concentration of CO at 1000Â°C will be
a) 0.573 M
b) 0.385 M
d) 0.295 M
26) For the reaction, 2X(g)+Y(g) 2Z(g);D H = – 80 k.cals. The highest yield of Z at equilibrium will occur at
27) For which of the following systems at equilibrium at constant temperature will decreasing the volume cause no shift ?
d) None is correct
28) @ The equilibrium constant for the reactions
SO2(g)+l/2O2(g) SO3(g) and 2SO2(g) 2SO3(g) + O2(g) are K1 and K2, respectively. Then
29) A reversible chemical reaction having two reactants is in equilibrium. If the concentrations are doubled than the equilibrium constant will
a) Also be doubled
b) Be halved
c) Becomes one fourth
d) Remains the same
30) In which equilibrium reaction would the equilibrium shift to the right, if the total pressure is increased ?
31) 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
32) The equilibrium constant for the reactions, N2(g) + O2(g) 2NO(g) and, NO(g)+l/2O2(g) NO2(g) are K1 and K2 respectively. The equilibrium constant for the equilibrium, N2(g) + 2O2(g) 2NO2(g) is
33) For which reaction are high pressure and high temperature helpful in obtaining a high equilibrium yield ?
34) An equilibrium mixture of the reaction, 2NO(g)+ O2(g) 2NO2(g) contains 0.120 mol of NO2, 0.080 mole of NO and 0.640 mol of O2 in a 4 litre flask at constant temperature. What is the value of Kc for the reaction at this temperature?
35) For a reaction 2A + B® C +D, the partial pressures of A, B, C and D at equilibrium are 0.5, 0.8, 0.7 and 1.2 atm. respectively. The value of Kp for the reaction is
36) In the manufacture of ammonia by Habers process,
N2 + 3H2 2NH3; D H = – 92.3k.cals, which of the following conditions is favourable for the yield of ammonia ?
a) Increasing temperature
b) Decreasing pressure
37) In a flask colourless N2O4 is in equilibrium with brown coloured NO2. At equilibrium, when the flask is heated at 100Â°C, the brown colour deepens and on cooling it becomes less coloured. The change in enthalpy for the system is
38) Which reaction gives more products as a result of increase in pressure ?
39) For H2+ I2 2HI, at equilibrium some I2 is added. What happens to the equilibrium ?
a) It is shifted to the right
b) It is shifted to the left
c) It remains unchanged
40) On adding an inert gas at constant volume to the reaction N2+ 3H2 2NH3 at equilibrium
a) The reaction stops
b) the forward reaction is favoured
c) The reaction remains unaffected
d) the backward reaction is favoured
41) In the dissociation of 2HI H2+ I2, the degree of dissociation will be influenced by
a) Addition of inert gas at constant volume
b) Addition of inert gas at constant pressure
c) Increase of temperature
d) Increase of pressure
42) If pressure is applied to the equilibrium, solid liquid, the melting point of the solid
a) Will increase
b) Will decrease
c) May not change
d) May increase or decrease depending upon its nature
43) If pressure is applied to the equilibrium Liquid Vapour, the boiling point of the liquid,
a) Will decrease
b) Will increase
c) May not change
d) Will not change
44) The solubility of a substance which dissolves with a decrease in volume and absorption of heat will be favoured by
a) High P and high T
b) Low P and low T
c) High P and low T
d) Low P and high T
45) For the equilibrium, PCl5 PCl3+Cl2 , Kc = a2/(l – a)V. If the temperature remains constant.
46) For the chemical reaction
3X(g)+ Y(g) X3Y(g), the amount of X3Y at equilibrium is affected by
a) Temperature and pressure
b) Temperature only
c) Pressure only
d) Temperature, pressure and catalyst
47) The tendency of a reaction to take place spontaneously is greatest, when the reaction is
a) Exothermic and randomness increases
b) Endothermic and randomness increases
c) Exothermic and randomness decreases
d) Endothermic and randomness decreases
48) Chemical equilibrium is dynamic in nature because
a) The equilibrium is maintained rapidly
b) The concentration of reactants and products become same at equilibrium
c) The concentration of reactants and products are constant but different
d) Both forward and backward reactions occur at all times with same speed
49) In a pair of immiscible liquids, a common solute dissolves in both and the equilibrium is reached. The concentration of the solute in the upper layer is
a) Same as in lower layer
b) Lower than the lower layer
c) Higher than the lower layer
d) In a fixed ratio with that in the lower layer
50) The reaction A + B C +D + Heat, has reached equilibrium. The reaction may be made to proceed forward by
a) Adding more C
b) Adding more D
c) Decreasing the temperature
d) Increasing the temperature
51) If one third of HI decomposes at a particular temperature, Kc for 2HI H2 + I2 is.
52) Whicg statement is wrong about the equilibrium state ?
b) The reaction ceases at equilibrium
c) the equilibrium constant is independent of the initial concentrations of the reactants
d) A catalyst has no effect on the equilibrium state
53) At constant temperature, for which of the following systems at equilibrium will doubling the volume cause the shift to the right ?
54) Amongst the following reactions, the one which will not be affected by the change in pressure of the reactant will be
55) For the reaction 2X + Y Z, the expression of the equilibrium constant will be
56) Which one of the following reversible reaction can not be affected by pressure ?
57) In the reaction 4NH3 (g) + 5O2(g) 4NO (g)+ 6H2O (l), when 1 mole of NH3 and 1 mole of O2 are made to react to completion,
b) 1.0 mole of NO will be produced
c) All the oxygen will be consumed
d) All the ammonia will be consumed
58) If K1 and K2 are the respective equilibrium constants for the reactions.
XeF6(g) + H20(g) XeOF4(g) + 2HF(g) —————–(1)
XeO4(g) + XeF6(g) XeOF4(g) + XeO3F2(g) ———-(2)
The equilibrium constant of the reaction
XeO4(g) + 2HF (g) XeO3F2(g) + H2O(g) will be.
59) On the basis of Le Chateliers principle, predict which one of the following conditions would be unfavourable for the formation of SO3 according to the reaction ?
2SO2 + O2 2SO3; D H = – 42 k . cals
a) Low temperature
b) High pressure
c) High temperature
60) If the equilibrium constant for the reaction 2AB A2 + B2 is 49, what is the value of the equilibrium constant for AB Â½ A2 + 1/2 B2 ?
61) @ 4.5 moles each of hydrogen and iodine are heated in a sealed ten litre vessel. At equilibrium 3 moles of HI were found. The equilibrium constant for the reaction H2(g) + I2(g) 2HI(g) is
62) For the reaction NH4Cl NH3 + HCl, an increase in pressure
a) Will shift the equilibrium from left to right
b) Will shift the equilibrium from right to left
c) Will not affect the equilibrium
d) Causes the equilibrium constant to be zero
63) For the reaction N2 + 3H2 2NH3, when pressure is increased,
a) font face=”Arial”>the forward reaction proceeds
b) the backward reaction proceeds
c) there is no effect
d) None of these
64) Formation of SO3 takes place according to the reaction
2SO2 + O2 2SO3; D H = -45.2 k.cals.
Which of the following factors favour the formation of SO3 ?
a) Increase in temperature
b) Increase in pressure
c) Removal of oxygen
d) Increase in volume
65) Kp/Kcfor the reaction CO(g) + l/2O2 (g) CO, (g) is.
66) The unit of equilibrium constant for the reaction H2 +I2 2HI is.
d) No unit
67) For the reaction, PCl3 (g) + Cl2(g) PCl5(g), the value of Kc at 250Â°C is 26 mole-1 litre-1.The value of Kp at this temperature will be
68) Consider the reaction, PCl5(g) PCl3(g) + Cl2(g) in a closed container at equilibrium. At a fixed temperature addition of more PCl5 at equilibrium will show … in equilibrium concentration of Cl2(g).
a) a decrease
b) an iIncrease
c) No change
69) @ The equilibrium constant for the reaction NO (g) + 1/2Cl2 (g) NOCl (g) at 25Â°C is 3.7 x 103. What is the equilibrium constant for the reaction 2NOCl (g) 2NO (g) + Cl2 (g) ?
b) 7.3 x 10-6
70) In which of the following cases does the reaction go farthest to completion ?
71) 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
72) Increasing 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 rate as the case may be
d) Favours neither the forward nor backward rates
73) A chemical system is in equilibrium. The addition of a catalyst would result in
a) Increase in the rate of forward reaction only
b) Increase in the rate of backward reaction only
c) A new reaction pathway to the reaction
d) Increase the amount of heat evolved in the reaction
74) 3 volumes of hydrogen are required to combine completely with 1 volume of nitrogen to form 2 volumes of ammonia. If one mole of hydrogen and one mole of nitrogen are taken, how many moles of ammonia will be formed if the reaction is taken to completion ?
a) 1/3 moles
b) 2/3 moles
c) 3/2 moles
d) 2 moles
75) The reaction A + 2B C + D is at equilibrium. The concentrations of the reactants and products are : [A] = 0.20; [B] = 0.10; [C] = 0.30 and [D] = 0.50. The value of the equilibrium constant is
76) The chemical reaction in which the yield of the product cannot be increased by the application of high pressure is
77) For which reaction is Kp = Kc ?
78) If the initial concentration of N2, H2 and NH3 are 1, 2 and 3 respectively, their concentrations at equilibrium of the following reaction will be
N2 + 3H2 2NH3
a) (1 – x), (2 – 3x) and 2x
b) (l-x/3), (2-x) and 2x/3
c) (l-x), (2-x)and (3 + x)
d) (l-x), (2-3x) and (3 + 2x)
79) Consider the reaction, CH3COOH + C2H5OH CH3COOC2H5+ H2O. One mole each of CH3COOH and C2H5OH are heated in the presence of a little concentrated H2SO4. On equilibrium.
a) 1 mole of ethyl acetate is formed
b) 2 moles of ethyl acetate are formed
c) 1/2 mole of ethyl acetate is formed
d) cannot be predicted without knowing the equilibrium constant
80) In a reversible gaseous reaction, the molar concentration or active masses of reactants and products are proportional to the
a) Partial pressure
b) Total pressure
c) Amount of reactants and products
81) For an endothermic reaction where D H represents the enthalpy of the reaction in kJ/mole,the minimum value of energy of activation will be
82) The Habers process for the manufacture of ammonia is usually carried out at 450-500Â°C. If a temperature of 250Â° C was used instead of 450-500Â°C.
83) In the chemical reaction, N2 + 3H2 2NH3 at equilibrium,
c) Reaction has stopped
d) The rate of ammonia formation is equal to the rate of NH3 decomposition into N2 and H2
84) At a constant temperature the concentration of a reactant is increased at equilibrium. The equilibrium constant
c) Remains unchanged
d) First increases and then decreases
85) A higher value for the equilibrium constant K shows that
a) The reaction has gone to near completion towards the right
b) The reaction has not yet started
c) The reaction has gone to near completion towards the left
86) In the reaction, N2(g) + 3H2(g) 2NH3 (g), an increase in the H2 concentration at equilibrium
b) Does not affect the reaction
c) Increases the equilibrium constant
87) According to Le Chatelier`s principle, adding heat to an endothermic reaction, solid liquid, will cause the
a) Amount of solid to decrease
b) Amount of liquid to decrease
c) Temperature to rise
d) Temperature to decrease
88) The equilibrium, SO2Cl2(g) SO2(g) + Cl2(g) is attained at 25Â°C in a closed container and an inert gas helium is introduced. Which of the following statements are correct ?
b) More chlorine is formed
d) All are incorrect
89) When NaNO3 is heated in a closed vessel, oxygen is liberated and NaNO2 is left behind.
c) Increasing the temperature favours the forward reaction
d) Decreasing the pressure favours the reverse reaction
90) The equilibrium constants for the reactions
H3PO4 H+ +H2PO–4 ;K1
H2PO–4 H+ + HPO2-4 ;K2
HPO2-4 H+ + PO3-4 ;K3
The equilibrium constant for the reaction, H3PO4 3H+ +PO3-4 is,
91) For the reaction, PCl5 (g) PCl3(g) +Cl2(g), the forward reaction at constant temperature is favoured by.
a) Introducing an inert gas at constant volume
b) Introducing chlorine gas at constant volume
c) Introducing an inert gas at constant pressure
92) The reaction which proceeds in the forward direction is
d) 2Cul+l2 2Cu2++4I<sup-< sup=””>
93) In a vessel containing SO3, SO2 and O2 at equilibrium, some helium gas is introduced so that the total pressure increases while temperature and volume remain constant. According to LeChateliers principle, the dissociation of SO3
c) Remains unaltered
d) Changes unpredictable
94) For the gaseous phase reaction, 2NO N2 + O2; D H = – 43.5 k . cal mole-1, which statement is correct for N2(g) + O2(g) 2NO(g)?
a) K is independent of temperature
b) K increases as temperature decreases
c) K decreases as temperature decreases
d) K varies with addition of NO
95) The following equilibrium exists in aqueous solution. CH3COOH CH3COO– + H+. If dilute HCl is added without a change in temperature then
a) the conc. of CH3COO– will decrease
b) The equilibrium constant will increase
c) The equilibrium constant will decrease
d) the conc. of CH3COO– will increase
96) In a lime kiln, the reversible reaction, CaCO3(g) CaO(s) + CO2(g), proceeds to completion, because
a) Of high temperature
b) CO2 escapes
c) CaO is removed
d) Of low temperature
97) The numerical values of Kp and Kc for the equilibrium, 2NH3 N2 + 3H2 are related as :
d) Any of these
98) The equilibrium constant for the reaction 2 X (g) + Y (g) 2Z (g) is 2.25. What would be the concentration of Y at equilibrium with 2.0 moles of X and 3.0 moles of Z in a one litre vessel ?
a) 0.9 moles
b) 2.25 moles
c) 2.0 moles
d) 4.0 moles
99) Consider the reaction, CaCO3 (s) CaO(s) + CO2 (g) in a closed container at equilibrium. At a fixed temperature, what will be the effect of adding more CaCO3 on the equilibrium concentration of CO2?
a) It increases
b) It decreases
c) It remains same
d) Cannot be predicted
100) @ At constant temperature, in a litre vessel when the reaction 2SO3(g) 2SO2(g) + O2(g) is at equilibrium, the SO2 concentration is 0.6 mole. The initial concentration of SO3 is 1 mole. What is the equilibrium constant value ?