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Equilibrium MCQs

Class 11 Chemistry — questions with answers and worked explanations.

20 free questions Class 11 Chemistry Answers + explanations No sign-up

These questions are drawn from the Pariksha Sutra question bank for Equilibrium, part of the Class 11 Chemistry syllabus. Each one shows the correct answer and, where a method helps, the working behind it.

Read the question, decide your answer before looking, then check the explanation — that is what turns practice into marks. If a question catches you out, the explanation is the part worth re-reading.

Questions

Question 1
In a closed vessel, liquid water and its vapour reach equilibrium. At this point, which statement is correct?
  1. No molecules move between phases
  2. Condensation stops completely
  3. Evaporation stops completely
  4. Rate of evaporation equals rate of condensation
Answer: Rate of evaporation equals rate of condensation
Question 2
For the reaction A <=> B, at equilibrium [A] = 0.5 mol/L and [B] = 1.5 mol/L. The value of Kc is:
  1. 1.5
  2. 0.33
  3. 3
  4. 0.75
Answer: 3
Question 3
The conjugate base of HCO3- is:
  1. H2CO3
  2. CO2
  3. OH-
  4. CO3 2-
Answer: CO3 2-
Question 4
If [H+] = 1 x 10^-5 mol/L, the pH of the solution is:
  1. 5
  2. 7
  3. 9
  4. 3
Answer: 5
Question 5
The Ka of acetic acid is 1.8 x 10^-5. The Kb of acetate ion is:
  1. 5.6 x 10^-10
  2. 1.8 x 10^-5
  3. 5.6 x 10^-5
  4. 1.8 x 10^-9
Answer: 5.6 x 10^-10
Question 6
If Kc for A <=> B is 4, then Kc for the reverse reaction B <=> A is:
  1. 16
  2. 4
  3. 2
  4. 0.25
Answer: 0.25
Question 7
In the reaction NH3 + H2O <=> NH4+ + OH-, water acts as a:
  1. Bronsted acid
  2. Bronsted base
  3. Lewis base
  4. Neutral spectator
Answer: Bronsted acid
Question 8
The pH of a 0.01 mol/L NaOH solution is:
  1. 7
  2. 12
  3. 2
  4. 10
Answer: 12
Question 9
For a conjugate acid-base pair, the relation between Ka and Kb at 25 degree C is:
  1. Ka/Kb = Kw
  2. Ka x Kb = 1
  3. Ka x Kb = Kw
  4. Ka + Kb = Kw
Answer: Ka x Kb = Kw
Question 10
For the sparingly soluble salt AgCl <=> Ag+ + Cl-, the solubility product Ksp equals:
  1. [AgCl]/[Ag+][Cl-]
  2. [Ag+][Cl-]
  3. [Ag+]/[Cl-]
  4. [Ag+]^2[Cl-]
Answer: [Ag+][Cl-]
Question 11
For the equilibrium H2O(l) <=> H2O(g) at constant temperature, which quantity remains constant?
  1. Volume of liquid
  2. Rate of condensation only
  3. Number of gas molecules
  4. Vapour pressure
Answer: Vapour pressure
Question 12
A very large value of the equilibrium constant (K >> 1) indicates that at equilibrium:
  1. Reactants predominate
  2. Equal amounts of both
  3. Products predominate
  4. No reaction occurs
Answer: Products predominate
Question 13
The conjugate acid of NH3 is:
  1. NH4+
  2. OH-
  3. NH2-
  4. N2H4
Answer: NH4+
Question 14
A solution has pH = 4. Its hydrogen ion concentration is:
  1. 1 x 10^4 mol/L
  2. 4 mol/L
  3. 1 x 10^-10 mol/L
  4. 1 x 10^-4 mol/L
Answer: 1 x 10^-4 mol/L
Question 15
The pKa of an acid with Ka = 1 x 10^-5 is:
  1. 9
  2. 5
  3. 10
  4. -5
Answer: 5
Question 16
Chemical equilibrium in a reversible reaction is best described as:
  1. A state with only products present
  2. Dynamic and reached from either direction
  3. Static and reached from one side only
  4. A state where the reaction stops
Answer: Dynamic and reached from either direction
Question 17
Adding a catalyst to a reaction at equilibrium:
  1. Decreases the value of Kc
  2. Increases the value of Kc
  3. Shifts equilibrium toward products
  4. Does not change Kc but hastens attainment of equilibrium
Answer: Does not change Kc but hastens attainment of equilibrium
Question 18
Which of the following can act as a Lewis acid?
  1. NH3
  2. OH-
  3. H2O
  4. BF3
Answer: BF3
Question 19
A solution with pH = 9.5 at 25 degree C is:
  1. Basic
  2. Acidic
  3. Cannot be determined
  4. Neutral
Answer: Basic
Question 20
Among acids with pKa values 2, 4, 6 and 8, the strongest acid has pKa:
  1. 6
  2. 4
  3. 2
  4. 8
Answer: 2

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