Equilibrium MCQs – Chemical and Ionic Equilibrium Class 11
Equilibrium MCQs – Chemical and Ionic Equilibrium (Class 11 Chemistry)
Course: CBSE Class 11 Chemistry – MCQs with Answers and Explanations
Section: Physical Chemistry – MCQ Titles
The following 50 Multiple Choice Questions (MCQs) are strictly based on the NCERT chapter “Equilibrium”, covering both Chemical Equilibrium and Ionic Equilibrium. The questions are arranged section-wise with clear, concept-clearing explanations, making them ideal for CBSE Class 11 board exam preparation.
Section A: Introduction to Equilibrium
1. Chemical equilibrium is established when
A. reaction stops completely
B. forward reaction rate equals reverse reaction rate
C. reactants are fully converted to products
D. concentration of reactants becomes zero
Answer: B
Explanation: At equilibrium, forward and reverse reactions occur at equal rates.
2. Equilibrium is dynamic in nature because
A. molecules stop moving
B. reaction stops
C. reactions continue at equal rates
D. temperature changes continuously
Answer: C
Explanation: Both reactions continue, but no net change is observed.
3. Which of the following reactions can attain equilibrium?
A. Irreversible reactions
B. Reversible reactions
C. Nuclear reactions
D. Spontaneous reactions only
Answer: B
Explanation: Only reversible reactions establish equilibrium.
Section B: Law of Mass Action and Equilibrium Constant
4. Law of mass action was proposed by
A. Le Chatelier
B. Guldberg and Waage
C. Arrhenius
D. Ostwald
Answer: B
Explanation: They formulated the law relating reaction rate to concentrations.
5. The equilibrium constant for the reaction
aA + bB ⇌ cC + dD is given by
A. [A]ᵃ[B]ᵇ / [C]ᶜ[D]ᵈ
B. [C]ᶜ[D]ᵈ / [A]ᵃ[B]ᵇ
C. [A][B] / [C][D]
D. ratio of forward to reverse rate
Answer: B
Explanation: Products raised to stoichiometric powers divided by reactants.
6. The value of equilibrium constant depends on
A. concentration
B. pressure
C. temperature
D. catalyst
Answer: C
Explanation: Equilibrium constant changes only with temperature.
7. If Kc > 1, the reaction
A. favours reactants
B. favours products
C. is incomplete
D. never reaches equilibrium
Answer: B
Explanation: Higher Kc means products are favoured.
Section C: Homogeneous and Heterogeneous Equilibrium
8. Homogeneous equilibrium involves reactants and products in
A. same phase
B. different phases
C. solid phase only
D. gaseous phase only
Answer: A
Explanation: All components are in the same phase.
9. In heterogeneous equilibrium, concentrations of which substances are omitted from Kc?
A. gases
B. liquids
C. solids and pure liquids
D. aqueous solutions
Answer: C
Explanation: Their concentrations remain constant.
10. Which is an example of heterogeneous equilibrium?
A. N₂ + 3H₂ ⇌ 2NH₃
B. H₂ + I₂ ⇌ 2HI
C. CaCO₃(s) ⇌ CaO(s) + CO₂(g)
D. NO₂ ⇌ N₂O₄
Answer: C
Explanation: Reactants and products exist in different phases.
Section D: Le Chatelier’s Principle
11. Le Chatelier’s principle predicts the effect of
A. catalyst
B. temperature
C. concentration, pressure, temperature
D. time
Answer: C
Explanation: It explains how equilibrium shifts on changing conditions.
12. Increasing pressure shifts equilibrium towards the side with
A. more moles of gas
B. fewer moles of gas
C. solids
D. liquids
Answer: B
Explanation: System reduces pressure by forming fewer gas molecules.
13. Increase in temperature shifts equilibrium in
A. exothermic reaction towards products
B. endothermic reaction towards reactants
C. endothermic reaction towards products
D. no change
Answer: C
Explanation: Heat acts as a reactant in endothermic reactions.
14. Addition of catalyst
A. shifts equilibrium
B. changes Kc
C. speeds up attainment of equilibrium
D. favours products
Answer: C
Explanation: Catalyst affects rate, not position of equilibrium.
Section E: Equilibrium in Gaseous Systems
15. Kp is related to Kc by
A. Kp = Kc
B. Kp = Kc(RT)
C. Kp = Kc(RT)Δn
D. Kp = Kc/(RT)
Answer: C
Explanation: Δn = moles of gaseous products − reactants.
16. If Δn = 0, then
A. Kp = Kc
B. Kp > Kc
C. Kp < Kc
D. Kp = 1
Answer: A
Explanation: (RT)⁰ = 1.
17. Increasing volume favours the reaction with
A. more moles of gas
B. fewer moles of gas
C. solids
D. liquids
Answer: A
Explanation: System shifts to increase pressure.
Section F: Ionic Equilibrium and Electrolytes
18. Ionic equilibrium exists in
A. non-electrolytes
B. strong electrolytes
C. weak electrolytes
D. metals
Answer: C
Explanation: Weak electrolytes partially ionise.
19. Strong electrolytes are those which
A. do not ionise
B. partially ionise
C. completely ionise
D. ionise only in solids
Answer: C
Explanation: Strong electrolytes dissociate fully.
20. Weak acids have
A. high Ka value
B. low Ka value
C. zero Ka value
D. infinite Ka value
Answer: B
Explanation: Smaller Ka indicates weak acid.
Section G: pH and Ionisation Constants
21. pH of a neutral solution at 25°C is
A. 0
B. 7
C. 14
D. 1
Answer: B
Explanation: Neutral solutions have equal [H⁺] and [OH⁻].
22. pH is defined as
A. −log[OH⁻]
B. log[H⁺]
C. −log[H⁺]
D. log[OH⁻]
Answer: C
Explanation: pH = −log[H⁺].
23. Which solution has the lowest pH?
A. 0.1 M HCl
B. 0.01 M HCl
C. 0.1 M NaOH
D. distilled water
Answer: A
Explanation: Higher [H⁺] means lower pH.
24. For weak acid HA, Ka is given by
A. [H⁺][A⁻]/[HA]
B. [HA]/[H⁺][A⁻]
C. [H⁺]²
D. [A⁻]/[H⁺]
Answer: A
Explanation: Expression for acid dissociation constant.
Section H: Degree of Ionisation and Ostwald’s Dilution Law
25. Degree of ionisation increases with
A. increase in concentration
B. decrease in temperature
C. dilution
D. addition of salt
Answer: C
Explanation: Dilution favours ionisation.
26. Ostwald’s dilution law is applicable to
A. strong electrolytes
B. weak electrolytes
C. salts
D. metals
Answer: B
Explanation: It relates ionisation of weak electrolytes to concentration.
27. Which factor does NOT affect degree of ionisation?
A. Nature of solvent
B. Nature of electrolyte
C. Temperature
D. Catalyst
Answer: D
Explanation: Catalysts do not affect equilibrium position.
Section I: Common Ion Effect and Buffer Solutions
28. Common ion effect is the suppression of
A. precipitation
B. ionisation of electrolyte
C. solubility
D. neutralisation
Answer: B
Explanation: Presence of common ion reduces ionisation.
29. Addition of sodium acetate to acetic acid decreases
A. pH
B. degree of ionisation
C. Ka
D. temperature
Answer: B
Explanation: Acetate ion suppresses ionisation of acetic acid.
30. A buffer solution resists change in
A. temperature
B. volume
C. pH
D. pressure
Answer: C
Explanation: Buffers maintain nearly constant pH.
31. Acidic buffer consists of
A. weak acid and strong base
B. strong acid and weak base
C. weak acid and its salt
D. strong acid and its salt
Answer: C
Explanation: Example: CH₃COOH + CH₃COONa.
Section J: Solubility Product and Applications
32. Solubility product applies to
A. soluble salts
B. weak acids
C. sparingly soluble salts
D. strong bases
Answer: C
Explanation: Ksp applies to slightly soluble salts.
33. Higher Ksp value means
A. lower solubility
B. higher solubility
C. no solubility
D. no equilibrium
Answer: B
Explanation: Larger Ksp indicates greater solubility.
34. Precipitation occurs when
A. ionic product < Ksp
B. ionic product = Ksp
C. ionic product > Ksp
D. Ksp = 0
Answer: C
Explanation: Supersaturation leads to precipitation.
35. Solubility of AgCl decreases in presence of
A. NaNO₃
B. NaCl
C. water
D. NH₃
Answer: B
Explanation: Cl⁻ is a common ion.
Section K: Conceptual NCERT-Based MCQs
36. Equilibrium constant for reverse reaction is
A. same as forward
B. reciprocal of forward
C. square of forward
D. zero
Answer: B
Explanation: K(reverse) = 1/K(forward).
37. Which factor changes equilibrium constant?
A. Pressure
B. Catalyst
C. Concentration
D. Temperature
Answer: D
Explanation: Only temperature affects K.
38. pH of basic solution is
A. less than 7
B. equal to 7
C. greater than 7
D. zero
Answer: C
Explanation: Basic solutions have pH > 7.
39. Which acid has maximum Ka?
A. CH₃COOH
B. H₂CO₃
C. HCl
D. HF
Answer: C
Explanation: HCl is a strong acid.
40. Which base is weakest?
A. NaOH
B. KOH
C. NH₄OH
D. Ca(OH)₂
Answer: C
Explanation: NH₄OH is a weak base.
41. Ionic equilibrium is an example of
A. physical equilibrium
B. chemical equilibrium
C. nuclear equilibrium
D. mechanical equilibrium
Answer: B
Explanation: It involves reversible chemical processes.
42. Buffer capacity depends on
A. temperature only
B. concentration of buffer components
C. pressure
D. catalyst
Answer: B
Explanation: Higher concentration gives higher buffer capacity.
43. Which solution acts as a buffer?
A. NaCl + HCl
B. NH₄Cl + NH₄OH
C. NaOH + HCl
D. NaCl + NaOH
Answer: B
Explanation: Weak base and its salt form a buffer.
44. Equilibrium constant is dimensionless when
A. Δn = 0
B. reaction is reversible
C. reaction is exothermic
D. temperature is high
Answer: A
Explanation: Units cancel out when Δn = 0.
45. Which reaction favours products at low temperature?
A. Endothermic
B. Exothermic
C. Neutral
D. Reversible only
Answer: B
Explanation: Lower temperature favours exothermic reactions.
46. Degree of dissociation of strong electrolytes is approximately
A. zero
B. 0.1
C. 0.5
D. 1
Answer: D
Explanation: Strong electrolytes ionise completely.
47. pH of 10⁻³ M HCl solution is
A. 1
B. 2
C. 3
D. 11
Answer: C
Explanation: pH = −log(10⁻³) = 3.
48. Equilibrium constant expression does NOT include
A. solids
B. gases
C. aqueous species
D. ions
Answer: A
Explanation: Solids have constant concentration.
49. Which factor does not disturb equilibrium position?
A. Pressure
B. Temperature
C. Concentration
D. Catalyst
Answer: D
Explanation: Catalyst does not shift equilibrium.
50. Chemical equilibrium is best described as
A. static
B. irreversible
C. dynamic
D. complete
Answer: C
Explanation: Forward and reverse reactions occur continuously.
✅ Completion Note
This completes a fully NCERT-aligned, CBSE-standard set of 50 MCQs on Equilibrium (Chemical and Ionic), ideal for concept clarity, revision, and board exam preparation.