CBSE Class 11 Chemistry Chemical Equilibrium MCQs

Question: Which of the following is not a general characteristic of equilibria involving physical processes ?

a) All the physical processes stop at equilibrium

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

c) All measurable properties of the system remain constant.

d) Equilibrium is possible only in a closed system at a given temperature.

Answer: All the physical processes stop at equilibrium

Question: The liquid which has a ____ vapour pressure is more volatile and has a_____boiling point.

a) Higher, lower

b) Higher , higher

c) Lower, lower

d) Lower, higher

Answer: Higher, lower

Question: Boiling point of the liquid depends on the atmospheric pressure. It depends on the altitude of the place; at high altitude the boiling point…………..

a) decreases

b) increases

c) either decreases or increases

d) remains same

Answer: decreases

Question: In an experiment three watch glasses containing separately 1mL each of acetone, ethyl alcohol, and water are exposed to atmosphere and the experiment with different volumes of the liquids in a warmer room is repeated, it is observed that in all such cases the liquid eventually disappears and the time taken for complete evaporation in each case was different. The possible reason is/are

a) All of the above

b) the temperature is different

c) the amount of the liquids is different

d) the nature of the liquids is different

Answer: All of the above

Question: A small amount of acetone is taken in a watch glass and it is kept open in atmosphere. Which statement is correct for the given experiment?

a) The rate of condensation from vapour to liquid state is much less than the rate of evaporation

b) The rate of condensation from vapour to liquid state is equal or less than the rate of evaporation.

c) The rate of condensation from vapour to liquid state is equal to the rate of evaporation

d) None of these

Answer: The rate of condensation from vapour to liquid state is much less than the rate of evaporation

Question: Reaction is said to be in equilibrium when

a) the rate of transformation of reactant to products is equal to the rate of transformation of products to the reactants.

b) 50% of the reactants are converted to products

c) the volume of reactants is just equal to the volume of the products

d) the reaction is near completion and all the reactants are converted to products

Answer: the rate of transformation of reactant to products is equal to the rate of transformation of products to the reactants.

Question: Which of the following is not true about a reversible reaction?

a) Number of moles of reactants and products is always equal

b) It can be attained only in a closed container

c) It cannot be influenced by a catalyst

d) The reaction does not proceed to completion

Answer: Number of moles of reactants and products is always equal

Question: If a system is at equilibrium, the rate of forward to the reverse reaction is

a) equal

b) less

c) high

d) at equilibrium

Answer: equal

Question: In a reversible chemical reaction having two reactants in equilibrium, if the concentration of the reactants are doubled then the equilibrium constant will

a) Remain the same

b) Be halved

c) Also be doubled

d) Become one-fourth

Answer: Remain the same

Question: On doubling P and V with constant temperature the equilibrium constant will

a) remain constant

b) become one-fourth

c) become double

d) None of these

Answer: remain constant

Question: The reaction quotient Q is used to

a) predict the direction of the reaction

b) calculate equilibrium concentrations

c) calculate equilibrium constant

d) predict the extent of a reaction on the basis of its magnitude

Answer: predict the direction of the reaction

Question: Which one of the following information can be obtained on the basis of Le Chatelier principle?

a) Shift in equilibrium position on changing value of a constraint

b) Equilibrium constant of a chemical reaction

c) Entropy change in a reaction

d) Dissociation constant of a weak acid

Answer: Shift in equilibrium position on changing value of a constraint

Question: Suitable conditions for melting of ice

a) high temperature and high pressure

b) high temperature and low pressure

c) low temperature and low pressure

d) low temperature and high pressure

Answer: high temperature and high pressure

Question: In an equilibrium reaction if temperature increases

a) any of the above

b) no effect

c) equilibrium constant decreases

d) equilibrium constant increases

Answer: any of the above

Question: What happens when an inert gas is added to an equilibrium keeping volume unchanged?

a) More product will form

b) Less product will form

c) More reactant will form

d) Equilibrium will remain unchanged

Answer: More product will form

Question: Which of the following is/are electrolytes?

(i) Sugar solution (ii) Sodium chloride

(iii) Acetic acid      (iv) Starch solution

a) (ii) and (iii)

b) (i) and (iv)

c) (ii) and (iv)

d) (i) and (iii)

Answer: (ii) and (iii)

Question: Which of the following statements are correct regarding Arrhenius theory of acid and base?

a) Both

b) This theory was applicable to only aqueous solutions

c) This theory was applicable to all solutions

d) None of these

Answer: Both

Question: Would gaseous HCl be considered as an Arrhenius acid ?

a) No

b) Yes

c) Not known

d) Gaseous HCl does not exist

Answer: No

Question: A base, as defined by Bronsted theory, is a substance which can

a) accept protons

b) gain a pair of electrons

c) donate protons

d) lose a pair of electrons

Answer: accept protons

Question: BF₃ is an acid according to

a) Lewis Concept

b) Arrhenius concept

c) Bronsted-Lowry concept

d) None of these

Answer: Lewis Concept

Question: For the chemical reaction 3X(g) + Y(g) ⇌ X₃ Y(g),the amount of X₃ Y at equilibrium is affected by
a. Temperature and pressure
b. Temperature only
c. Pressure only
d. Temperature, pressure and catalyst
Answer : A

Question: In the reaction N₂ + 3H₂ → 2NH₃ , the product increases on:
a. Increasing temperature
b. Increasing pressure
c. Increasing temperature and pressure both
d. Decreasing temperature and pressure both
Answer : B

Question: In which of the following system, doubling the volume of the container cause a shift to the right:
a. H₂ (g) + Cl₂ (g) = 2HCl(g)
b. 2CO(g) + O₂ (g) = 2CO₂ (g)
c. N₂ (g) + 3H₂ (g) = 2NH₃ (g)
d. PCl₅ (g) ⇌ PCl₃ (g) + Cl₂ (g)
Answer : D

Question: The equilibrium SO₂ Cl_2(g) ⇌ SO_2(g) + Cl_2(g) is attained at 25°C in a closed container and an inert gas helium is introduced which of the following statement is correct:
a. More chlorine is formed
b. Concentration of SO₂ is reduced
c. More SO₂ Cl₂ is formed
d. Concentration of SO₂ Cl₂ , SO₂ and Cl₂ does not change
Answer : D

Question: Which of the following equilibria will shift to right side on increasing the temperature?

Answer : C

Question: h_2(g) + I_2(g) ⇌ 2HI_(g) ΔH = + q cal, then formation of HI:
a. Is favoured by lowering the temperature
b. Is favoured by increasing the pressure
c. Is unaffected by change in pressure
d. Is unaffected by change in temperature
Answer : C

Question: In which of the following equilibrium systems is the rate of the backward reaction favoured by increase of pressure?
a. PCl₅ ⇌ PCl₃ + Cl₂
b. 2SO₂ + O₂ ⇌ 2SO₃
c. N₂ + 3H₂ ⇌ 2NH₃
d. N₂ + O ⇌ 2NO
Answer : A

Question: Which of the following equilibrium is not shifted by increase in the pressure?
a. H_2(g) + I_2(g) ⇌ 2HI_(g)
b. N_2(g) + 3H_2(g) ⇌ 2NH_3(g)
c. 2CO(g) + O_2(g) ⇌ 2CO_2(g)
d. 2C_(S) + O_2(g) ⇌ 2CO_(g)
Answer : A

Question: According to Le–Chatelier’s principal adding heat to a solid and liquid in equilibrium with endothermic nature will cause the:
a. Temperature to rise
b. Temperature to fall
c. Amount of solid to decrease
d. Amount of liquid to decrease
Answer : C

Question: On addition of an inert gas at constant volume to the reaction N₂ + 3H ⇌ 2NH at equilibrium:
a. The reaction remains unaffected
b. Forward reaction is favoured
c. The reaction halts
d. Backward reaction is favoured
Answer : A

Question: N₂ O₄ ⇌ 2NO₂ ,K_c = 4. This reversible reaction is studied graphically as shown in the figure. Select the correct statements:

a. Reaction quotient has maximum value at point A
b. Reaction proceeds left to right at a point when [N₂ O₄ ] = [NO₂] = 0.1M
c. K_c = Q when point D or F is reached
d. Reaction quotient has minimum value at a point B
Answer : B, C, D

Question: Two gases A and B in the molar ratio 1:2 were admitted to an empty vessel and allowed to reach equilibrium at  400ºC and 8 atm pressure as A(g) + 2B(g) ⇌ 2C(g). The mole fraction of ‘C’ at equilibrium is 0.4. The correct statements are:
a. Equilibrium constant K_p 5/8 atm⁻¹
b. The pressure at equilibrium when mole fraction of A is 0.1 is 196 atm
c. Partial pressure of ‘C’ is 16/5 atm
d. Partial pressure of A is 4/5 atm
Answer : A, B, C

Question: For the dissociation N₂ O₅ (g) ⇌ 2NO₂ (g) + (1/2) O₂ (g)  if, M = Molecular mass of N₂ O₅ (g) D = Vapour density of equilibrium mixture P_o = Initial pressure of N₂ O₅ (g) Identify the ‘true’ statements:
a. Equilibrium pressure can be expressed as P⁰M/2D
b. Equilibrium pressure can be expressed as 2 P⁰D/M
c. Degree of dissociation can be expressed as P⁰ (M-2D)/3D
d. Increase in temperature will lower the magnitude of D
Answer : A, D

Question: Consider the exothermic reaction: [Consider initially only CoCl²⁻_{4 (aq)} will increase]
a. If HCl is added to above equilibrium then concentration of CoCl²⁻_{4 (aq)} will increase
b. On dilution with water, the concentration of CoCl²⁻_{4 (aq)} will decrease
c. On doubling the volume of solution by addition of water the final concentration of [Co (H₂ O) ₆]2+ will be more than before equilibrium concentration
d. On increasing temperature the concentration of  CoCl²⁻_{4 (aq)} will decrease
Answer : A, B

Question: For the gas phase reaction carried out in vessel, the equilibrium concentration of C₂H₄ can be increased by:
a. Increasing the temperature
b. Decreasing the pressure
c. Adding some H₂
d. Adding some C₂ H₆
Answer : A, B, D

Question: For the reaction 2SO₃ ⇌ 2SO₂ + O₂ The forward reaction at constant temperature is favoured by:
a. Introducing an inert gas at constant volume
b. Introducing SO2 gas at constant volume
c. Increasing the volume of the container
d. Introducing SO3 at constant volume
Answer : C, D

Question: For the given reversible endothermic reactions taking place in a closed vessel
Reaction I         Reaction II       Reaction II
   A  ⇌   B           A  ⇌    C           B   ⇌   C
Equilibrium constants are K₁ , K₂ , K₃ respectively:
a. ΔH is higher for the reaction III
b. Concentration of B increases with increase in temperature at constant volume
c. Mole fraction of A at equilibrium is 1 / 1 + K₁ + K₂
d. With increase in temperature the ratio [B]/[C] decreases
Answer : C, D

Question: When NaNO₃ is heated in a closed vessel, O₂ is liberated and NaNO₂ is left behind. At equilibrium?
a. Addition of NaNO₃ favours forward reaction
b. Addition of NaNO₂ favours reverse reaction
c. Increasing pressure favours reverse reaction
d. Increasing temperature favours forward reaction
Answer : ALL

Question: The formation of NO₂ in the reaction 2NO + O₂ ⇌ 2NO₂ + heat is favoured by:
a. Low pressure
b. High pressure
c. Low temperature
d. Reduction in the mass of
Answer : B, C

Question: Two gaseous equilibria SO_2(g) + (1/2) O_2(g) ⇌ SO_3(g) and 2SO_3(g) ⇌ 2SO_2(g) +O_2(g) have equilibrium constants K₁ and K₂ respectively at 298K.Which of the following relationships between K₁ and K₂is correct?
a. K₁ = K₂
b. K₂ = K²₁
c. K₂ = 1/K²₁
d. K₂ = 1/K₁
Answer : C

Question: For the reaction: A + B + Q ⇌ C+ D, if the temperature is increased, then concentration of the products will:
a. Increase
b. Decrease
c. Remain same
d. Become Zero
Answer : A

Question: H_2(g) I_2(g) ∂ ⇌ 2HI_(g) In this reaction when pressure increases, the reaction direction:
a. Does not change
b. Forward
c. Backward
d. Decrease
Answer : A

Question: The rate of reaction of which of the following is not affected by pressure?
a. PCl₃ + Cl₂ ⇌ PCl₅
b. N₂ + 3H₂ ⇌ 2NH₃
c. N₂ + O₂ ⇌ 2NO
d. 2 2 3 2SO +O ⇌ 2SO₃
Answer : C

Question: The formation of nitric oxide by contact process N₂ + O₂ ⇌ 2NO. Δ H = 43.200 kcal is favoured by:
a. Low temperature and low pressure
b. Low temperature and high pressure
c. High temperature and high pressure
d. High temperature and excess reactants concentration
Answer : D

Question: Which reaction is not effected by change in pressure?
a. H₂ + I₂ ⇌ 2HI
b. 2C + O₂ ⇌ 2CO
c. N₂ + 3H₂ ⇌ 2NH₃
d. PCl₅ ⇌ PCl₃ + CI₂
Answer : A

Assertion and Reason

Note: Read the Assertion (A) and Reason (R) carefully to mark the correct option out of the options given below:
a. If both assertion and reason are true and the reason is the correct explanation of the assertion.
b. If both assertion and reason are true but reason is not the correct explanation of the assertion.
c. If assertion is true but reason is false.
d. If the assertion and reason both are false.
e. If assertion is false but reason is true.

Question: Assertion: K_p = K_c for all reaction.
Reason: At constant temperature, the pressure of the gas is proportional to its concentration.
Answer : E

Question: Assertion: On cooling a freezing mixture, colour of the mixture turns to pink from deep blue for a reaction. Co(H₂ O)²⁺_{6 (aq)} + 4Cl⁻_(aq) ⇌ CoCl^2-_4(aq) − + 6H₂ O_(l) .
Reason: Reaction is endothermic so on cooling, the reaction moves to backward direction.
Answer : A

Question: Assertion: If Qc (reaction quotient) < KC (equilibrium constant) reaction moves in direction of reactants.
Reason: Reaction quotient is defined in the same way as equilibrium constant at any stage of the reaction.
Answer : E

Question: Assertion: NaCl solution can be purified by passage of hydrogen chloride through brine.
Reason: This type of purification is based on Lehaterlier's principle.
Answer : C

Question: Assertion: Equilibrium constant has meaning only when the corresponding balanced chemical equation is given.
Reason: Its value changes for the new equation obtained by multiplying or dividing the original equation by a number.
Answer : A

Question: Assertion: Catalyst affects the final state of the equilibrium.
Reason: It enables the system to attain a new equilibrium state by complexing with the reagents.
Answer : D

Question: Assertion: For the reaction, 2NH₃ (g) ⇌ N₂ (g) +3H₂ (g), the unit of K_p will be atm.
Reason: Unit of K_p is (atm)Δn.
Answer : E

Question: Assertion: Effect of temperature of K_c or K_p depends on enthalpy change.
Reason: Increase in temperature shifts the equilibrium in exothermic direction and decrease in temperature shifts the equilibrium position in endothermic direction.
Answer : C

Question: Assertion: For a gaseous reaction, xA + yB ⇌ lC + mD, K_p = K_C.
Reason: Concentration of gaseous reactant is taken to be unity. 
Answer : D

Question: Assertion: SO₂ (g) + 1/2 O₂ (g) ⇌ SO₃ (g) + heat. Forward reaction is favoured at high temperature and low pressure.
Reason: Reaction is exothermic.
Answer : E

Comprehension Based

Paragraph-I

Decomposition of ammonium chloride is an endothermic reaction. The equilibrium may be represented as: NH₄ Cl(s) ⇌ NH₃ (g) + HCl(g) A 6.250 g sample of NH₄ Cl is placed in an evaculated 4.0. L container at 27°C. After equilibrium the total pressure inside the container is 0.820 bar and some solid remains in the container. Answer the followings.

Question: The value of K_p for the reaction at 300 K is:
a. 16.2
b. 0.168
c. 1.68
d. 32.4
Answer : B

Question: The amount of solid NH₄ Cl left behind in the container at equilibrium is:
a. 2.856
b. 28.56
c. 0.2856
d. 1.320
Answer : A

Question: If the volume of container were doubled at constant temperature, then what would happen to the amount of solid in the container?
a. Decrease
b. Increases
c. Remain unchanged
d. None
Answer : A

Question: The extent of decomposition can be increased by:
a. Increasing the temperature
b. Decreasing the temperature
c. Adding more NH₄ Cl
d. Removing HCl(g)
Answer : A

Question: The value of K_p for the reaction decreases with:
a. Increase in volume
b. Decrease in temperature
c. Decrease in pressure
d. Increase in temperature
Answer : B

Integer

Question: When PCl5 is heated it dissociates into PCl₃ and Cl₂. The density of the gas mixture at 200ºC and at 250ºC is 70.2 and 57.9 respectively. Find the degree of dissociation at 200ºC and 250ºC:
Answer : 1

Question: The degree of dissociation of PCl₅ is 60%, then find out the observed molar mass of the mixture:
Answer : 129

Question: At 444ºC 15g mole of hydrogen are mixed with 5.2g mole of I₂ vapour. When equilibrium was established,10g mole of HI was formed. Calculate the equilibrium constant for the reaction?
Answer : 50

Question: The degree of dissociation is 0.4 at 400K and 1 atm for the gaseous reaction PCl₅ ⇌ PCl₃ + Cl₂ Assuming ideal behaviour of all the gases, calculate the density of equilibrium mixture at 400K and 1 atm pressure: (Atomic mass of P =31 and Cl =35.5)
Answer : 5

Question: The value of K_p for the reaction 2H₂ O(g) + 2Cl₂ (g) ⇌ 4HCl(g) + O₂ (g) is 0.035 atm at 400°C, when the partial pressures are expressed in atmosphere. Calculate c K for the reaction, (1/2) O₂ (g) 2HCl(g) ⇌ Cl₂ (g) + H₂ O(g) ?
Answer : 40

Match the Column

Question: The section questions each with two columns I and II.
Match the items given in column I with that of column II.
      Column I                   Column II
(A) Q = K                 1. Reaction is nearer to com-pletion
(B) Q < K Q < K       2. Reaction is not at equilibrium
(C) Q > K                 3. Reaction is fast in forward direction
(D) K >>> l               4. Reaction at equilibrium
                                 5. Reaction proceeds in back-ward direction
a. A→4; B→2-3; C→2-5; D→1
b. A→2; B→4; C→3; D→1
c. A→1; B→3; C→2; D→4
d. A→4; B→1; C→3; D→2
Answer : A

Question: Match the statement of Column I with those in Column II:
                     Column I                             Column II
(A) CaCO₃ (s) ⇌ CaO(s) + CO₂ (g)      1. moL⁻¹
(B) NH₄ Cl(g) ⇌ NH₃ (g) + HCl(g)         2. Unitless
(C) H₂ (g) + I₂ (g) ⇌ 2HI(g)                    3. atm
(D) N₂ (g) + 3H₂ (g) ⇌ 2NH₃ (g)            4. atm⁻²
a. A→1-3; B→1-3; C→2; D→4
b. A→2; B→4; C→3; D→1
c. A→1; B→3; C→2; D→4
d. A→4; B→1; C→3; D→2
Answer : A

Question: Match the statement of Column I with those in Column II:
                Column I                        Column II
(A) Reaction is reversed .               1. (K)^{1 / 2}
(B) Reaction is divided by 2            2. K²
(C) Reaction is multiplied by 2        3. 1 / K
a. A→3; B→1; C→2
b. A→2; B→4; C→3
c. A→1; B→3; C→2
d. A→3; B→1; C→3
Answer : A