Chapter 6: Equilibrium Assertion-Reason Questions | chemistry Class 11 CBSE

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 1

Logic Check

Assertion (A): Equilibrium can only be established in a closed system. Reason (R): In an open system, molecules of vapour escape into the surroundings, so the rate of condensation never equals the rate of evaporation.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 2

Logic Check

Assertion (A): The equilibrium constant Kc for a given reaction is independent of initial concentrations of reactants and products. Reason (R): At a given temperature, Kc has a unique constant value determined only by temperature.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 3

Logic Check

Assertion (A): Adding an inert gas at constant pressure to a gaseous equilibrium mixture shifts the equilibrium toward the side with more moles of gas. Reason (R): At constant pressure, adding an inert gas increases the total volume, thereby decreasing the partial pressures of all reacting species.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 4

Logic Check

Assertion (A): A catalyst does not change the equilibrium constant Kc of a reaction. Reason (R): A catalyst increases the rate of both the forward and reverse reactions equally by lowering the activation energy by the same amount for both.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 5

Logic Check

Assertion (A): For the reaction H2(g) + I2(g) ⇌ 2HI(g), Kp equals Kc. Reason (R): When the number of moles of gaseous products equals the number of moles of gaseous reactants (Δn = 0), Kp = Kc(RT)0 = Kc.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 6

Logic Check

Assertion (A): Strong acids have very weak conjugate bases. Reason (R): When a strong acid dissociates completely, the resulting anion (conjugate base) has very little tendency to accept a proton back.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 7

Logic Check

Assertion (A): The equilibrium constant for the reverse reaction is equal to the equilibrium constant for the forward reaction. Reason (R): Reversing a reaction means products become reactants, which gives a new expression that is the reciprocal of the original Kc.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 8

Logic Check

Assertion (A): Increasing the temperature of an exothermic reaction at equilibrium decreases the value of Kc. Reason (R): Increasing temperature shifts the equilibrium toward the endothermic (reverse) direction, resulting in a smaller ratio of products to reactants at the new equilibrium.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 9

Logic Check

Assertion (A): The pH of 0.1 M HCl is lower than the pH of 0.1 M CH3COOH. Reason (R): HCl is a strong acid that completely dissociates, giving a higher [H+] than CH3COOH, which only partially ionizes.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 10

Logic Check

Assertion (A): For the reaction N2(g) + 3H2(g) ⇌ 2NH3(g), increasing pressure increases the yield of NH3. Reason (R): Increasing pressure shifts equilibrium toward the side with fewer moles of gas, which is the product side (2 moles vs. 4 moles of reactants).

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 11

Logic Check

Assertion (A): The solubility of AgCl decreases significantly when NaCl is added to the solution. Reason (R): NaCl provides Cl− ions (common ion), which shifts the dissolution equilibrium AgCl(s) ⇌ Ag+(aq) + Cl−(aq) to the left.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 12

Logic Check

Assertion (A): Water can act both as a Brønsted-Lowry acid and a base. Reason (R): Water has a lone pair of electrons on the oxygen atom, making it a Lewis base only.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 13

Logic Check

Assertion (A): The pH of a buffer solution does not change on dilution. Reason (R): On dilution, the ratio of [salt]/[acid] in a buffer remains constant, so pH = pKa + log([A−]/[HA]) remains unchanged.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 14

Logic Check

Assertion (A): The solubility of a sparingly soluble salt of a weak acid increases at lower pH. Reason (R): At lower pH, the concentration of H+ increases, which protonates the anion X−, reducing [X−] and shifting the dissolution equilibrium to the right.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 15

Logic Check

Assertion (A): For the thermal decomposition CaCO3(s) ⇌ CaO(s) + CO2(g), adding more solid CaCO3 at constant temperature does not change the equilibrium. Reason (R): The molar concentration of a pure solid is constant and independent of the amount present, so it is excluded from the equilibrium constant expression.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 16

Logic Check

Assertion (A): Kp > Kc for the reaction N2O4(g) ⇌ 2NO2(g). Reason (R): Δn = 2 − 1 = +1 for this reaction, and Kp = Kc(RT)Δn; since RT > 1 at temperatures above 12 K, Kp > Kc.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 17

Logic Check

Assertion (A): A solution of ammonium chloride (NH4Cl) is acidic. Reason (R): NH4+ ion undergoes hydrolysis to give NH4OH and H+ ions; since NH4OH is a weak base that remains mostly un-ionized, H+ accumulates in solution.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 18

Logic Check

Assertion (A): Degree of ionization of a weak acid increases on dilution. Reason (R): Dilution decreases the concentration c, and since α = √(Ka/c), a decrease in c leads to an increase in α.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 19

Logic Check

Assertion (A): Removing ammonia from the Haber process reaction vessel increases the yield of ammonia. Reason (R): Removing ammonia increases Kc, causing more N2 and H2 to react.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 20

Logic Check

Assertion (A): In the contact process, very high temperature (above 700°C) is avoided even though it increases the reaction rate. Reason (R): The reaction 2SO2 + O2 ⇌ 2SO3 is exothermic; very high temperature shifts equilibrium toward reactants, decreasing the yield of SO3.

Reasoning Options

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Chapter sections

Chapter 6: Equilibrium | Assertion-Reason

Assertion (A): Equilibrium can only be established in a closed system. Reason (R): In an open system, molecules of vapour escape into the surroundings, so the rate of condensation never equals the rate of evaporation.

Assertion (A): The equilibrium constant Kc for a given reaction is independent of initial concentrations of reactants and products. Reason (R): At a given temperature, Kc has a unique constant value determined only by temperature.

Assertion (A): Adding an inert gas at constant pressure to a gaseous equilibrium mixture shifts the equilibrium toward the side with more moles of gas. Reason (R): At constant pressure, adding an inert gas increases the total volume, thereby decreasing the partial pressures of all reacting species.

Assertion (A): A catalyst does not change the equilibrium constant Kc of a reaction. Reason (R): A catalyst increases the rate of both the forward and reverse reactions equally by lowering the activation energy by the same amount for both.

Assertion (A): For the reaction H2(g) + I2(g) ⇌ 2HI(g), Kp equals Kc. Reason (R): When the number of moles of gaseous products equals the number of moles of gaseous reactants (Δn = 0), Kp = Kc(RT)0 = Kc.

Assertion (A): Strong acids have very weak conjugate bases. Reason (R): When a strong acid dissociates completely, the resulting anion (conjugate base) has very little tendency to accept a proton back.

Assertion (A): The equilibrium constant for the reverse reaction is equal to the equilibrium constant for the forward reaction. Reason (R): Reversing a reaction means products become reactants, which gives a new expression that is the reciprocal of the original Kc.

Assertion (A): Increasing the temperature of an exothermic reaction at equilibrium decreases the value of Kc. Reason (R): Increasing temperature shifts the equilibrium toward the endothermic (reverse) direction, resulting in a smaller ratio of products to reactants at the new equilibrium.

Assertion (A): The pH of 0.1 M HCl is lower than the pH of 0.1 M CH3COOH. Reason (R): HCl is a strong acid that completely dissociates, giving a higher [H+] than CH3COOH, which only partially ionizes.

Assertion (A): For the reaction N2(g) + 3H2(g) ⇌ 2NH3(g), increasing pressure increases the yield of NH3. Reason (R): Increasing pressure shifts equilibrium toward the side with fewer moles of gas, which is the product side (2 moles vs. 4 moles of reactants).

Assertion (A): The solubility of AgCl decreases significantly when NaCl is added to the solution. Reason (R): NaCl provides Cl− ions (common ion), which shifts the dissolution equilibrium AgCl(s) ⇌ Ag+(aq) + Cl−(aq) to the left.

Assertion (A): Water can act both as a Brønsted-Lowry acid and a base. Reason (R): Water has a lone pair of electrons on the oxygen atom, making it a Lewis base only.

Assertion (A): The pH of a buffer solution does not change on dilution. Reason (R): On dilution, the ratio of [salt]/[acid] in a buffer remains constant, so pH = pKa + log([A−]/[HA]) remains unchanged.

Assertion (A): The solubility of a sparingly soluble salt of a weak acid increases at lower pH. Reason (R): At lower pH, the concentration of H+ increases, which protonates the anion X−, reducing [X−] and shifting the dissolution equilibrium to the right.

Assertion (A): Kp > Kc for the reaction N2O4(g) ⇌ 2NO2(g). Reason (R): Δn = 2 − 1 = +1 for this reaction, and Kp = Kc(RT)Δn; since RT > 1 at temperatures above 12 K, Kp > Kc.

Assertion (A): A solution of ammonium chloride (NH4Cl) is acidic. Reason (R): NH4+ ion undergoes hydrolysis to give NH4OH and H+ ions; since NH4OH is a weak base that remains mostly un-ionized, H+ accumulates in solution.

Assertion (A): Degree of ionization of a weak acid increases on dilution. Reason (R): Dilution decreases the concentration c, and since α = √(Ka/c), a decrease in c leads to an increase in α.

Assertion (A): Removing ammonia from the Haber process reaction vessel increases the yield of ammonia. Reason (R): Removing ammonia increases Kc, causing more N2 and H2 to react.

Assertion (A): In the contact process, very high temperature (above 700°C) is avoided even though it increases the reaction rate. Reason (R): The reaction 2SO2 + O2 ⇌ 2SO3 is exothermic; very high temperature shifts equilibrium toward reactants, decreasing the yield of SO3.

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