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Equilibrium ISC Class 11 MCQ & Practice Questions

Practice Equilibrium MCQs for ISC Class 11 Chemistry with answers, explanations, chapter revision and related ChemNexa mock tests.

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Equilibrium Revision Guide for ISC Class 11 Chemistry

Equilibrium covers reversible chemical processes and the quantitative relationship between reactants and products at equilibrium. It also includes acid-base, ionic and solubility equilibria in many syllabi.

For ISC Class 11 Chemistry, build confidence with equilibrium constants, reaction quotient, Le Chatelier principle, pH calculations, buffer concepts and solubility product.

Important Topics

  • Dynamic chemical equilibrium
  • Kc, Kp and reaction quotient
  • Le Chatelier principle
  • Acid-base equilibrium and pH
  • Buffer solutions
  • Solubility product and common-ion effect

Important Formulae & Relationships

  • Kp = Kc(RT)^Δn
  • pH = −log[H+]
  • pOH = −log[OH−]
  • pH + pOH = 14 at 25°C
  • Ka × Kb = Kw for a conjugate pair

Use formulas only after checking the required units, sign convention and assumptions for the question.

What to practise in Equilibrium

Concept Revision

Revise definitions, principles, equations, trends and core ideas from Equilibrium before attempting MCQs.

Exam-style MCQs

Use chapter-focused multiple-choice practice to improve accuracy, recall and application for ISC Class 11 Chemistry.

Performance Practice

Attempt ChemNexa tests, review results and return to weak areas for another round of targeted revision.

Top 20 Equilibrium MCQs with Answers

These public questions are selected from the exact Equilibrium chapter, screened for topic relevance and deduplicated so repeated versions of the same MCQ are not shown publicly. Use them for quick revision, then sign in to attempt the complete test experience with more questions, results and performance review.

ISC Class 11 Chemistry · Equilibrium · Very Hard

1. For gaseous equilibrium, Kp and Kc are related by:

  • A. Kp = Kc(RT)^Δn
  • B. Kp = Kc/RT always
  • C. Kp = Kc + RT
  • D. KpKc = RT
Answer: A
Explanation: For ideal gases, Kp=Kc(RT)^Δn where Δn is gaseous product moles minus gaseous reactant moles.

ISC Class 11 Chemistry · Equilibrium · Very Hard

2. A catalyst added to a system already at equilibrium:

  • A. Decreases K
  • B. Shifts equilibrium only to products
  • C. Does not change K or equilibrium composition
  • D. Increases K
Answer: C
Explanation: A catalyst speeds forward and reverse reactions similarly and does not alter the thermodynamic equilibrium constant.

ISC Class 11 Chemistry · Equilibrium · Very Hard

3. Increasing pressure shifts a gaseous equilibrium toward the side with:

  • A. Higher molecular masses only
  • B. Fewer moles of gas
  • C. More moles of gas
  • D. More solids
Answer: B
Explanation: Le Chatelier's principle predicts a shift that tends to reduce the imposed pressure.

ISC Class 11 Chemistry · Equilibrium · Very Hard

4. For an exothermic forward reaction, increasing temperature generally shifts equilibrium:

  • A. Toward products
  • B. Nowhere
  • C. Only if a catalyst is present
  • D. Toward reactants
Answer: D
Explanation: Heat behaves like a product in an exothermic reaction; heating favours the reverse direction.

ISC Class 11 Chemistry · Equilibrium · Very Hard

5. The conjugate base of H2CO3 is:

  • A. OH-
  • B. HCO3-
  • C. CO3^2-
  • D. H3O+
Answer: B
Explanation: Removal of one proton from H2CO3 gives HCO3-.

ISC Class 11 Chemistry · Equilibrium · Very Hard

6. For aA + bB ⇌ cC + dD, Kc is:

  • A. Sum of product concentrations
  • B. [C]^c[D]^d/[A]^a[B]^b
  • C. [A]^a[B]^b/[C]^c[D]^d
  • D. [C][D]/[A][B] irrespective of coefficients
Answer: B
Explanation: The law of mass action raises equilibrium concentrations to their stoichiometric coefficients.

ISC Class 11 Chemistry · Equilibrium · Very Hard

7. If Δn = 0 for a gaseous reaction:

  • A. Kp = KcRT
  • B. Kp = Kc/(RT)
  • C. Kp is always zero
  • D. Kp = Kc
Answer: D
Explanation: When Δn=0, (RT)^0=1.

ISC Class 11 Chemistry · Equilibrium · Very Hard

8. For an endothermic forward reaction, increasing temperature generally:

  • A. Leaves equilibrium constant unchanged
  • B. Stops the reaction
  • C. Favours products
  • D. Favours reactants
Answer: C
Explanation: Heat acts like a reactant, so increasing temperature favours the endothermic direction.

ISC Class 11 Chemistry · Equilibrium · Very Hard

9. Physical equilibrium between liquid and vapour is dynamic because:

  • A. All molecular motion stops
  • B. Only evaporation occurs
  • C. Only condensation occurs
  • D. Evaporation and condensation continue at equal rates
Answer: D
Explanation: At equilibrium both opposing processes continue at equal rates.

ISC Class 11 Chemistry · Equilibrium · Very Hard

10. The conjugate acid of NH3 is:

  • A. NH4+
  • B. NH2-
  • C. N2H4
  • D. HNO3
Answer: A
Explanation: Addition of one proton to NH3 gives NH4+.

ISC Class 11 Chemistry · Equilibrium · Very Hard

11. pOH is defined as:

  • A. -log10[OH-]
  • B. log10[OH-]
  • C. 14-pKw
  • D. [OH-]/[H+]
Answer: A
Explanation: pOH is the negative base-10 logarithm of hydroxide-ion concentration/activity.

ISC Class 11 Chemistry · Equilibrium · Very Hard

12. At 25°C for dilute aqueous solutions:

  • A. pH × pOH = 14
  • B. pH = pOH always
  • C. pH + pOH = 7
  • D. pH + pOH = 14
Answer: D
Explanation: Because pKw=14 at 25°C, pH+pOH=pKw.

ISC Class 11 Chemistry · Equilibrium · Very Hard

13. If

  • A. 11
  • B. 3
  • C. 7
  • D. 14
Answer: A
Explanation: pOH=3 and pH=14-3=11.

ISC Class 11 Chemistry · Equilibrium · Very Hard

14. For conjugate acid-base pair HA/A- in water:

  • A. Ka/Kb = Kw always
  • B. Ka = Kb always
  • C. Ka × Kb = Kw
  • D. Ka + Kb = Kw
Answer: C
Explanation: The dissociation constants of a conjugate pair multiply to Kw.

ISC Class 11 Chemistry · Equilibrium · Very Hard

15. The common ion effect generally:

  • A. Always increases ionisation
  • B. Changes atomic number
  • C. Destroys equilibrium
  • D. Suppresses ionisation of a weak electrolyte
Answer: D
Explanation: Adding an ion already present shifts the ionisation equilibrium toward the unionised form.

ISC Class 11 Chemistry · Equilibrium · Very Hard

16. A buffer solution primarily resists changes in:

  • A. Mass
  • B. pH
  • C. Temperature
  • D. Pressure
Answer: B
Explanation: Buffers consume modest added acid or base, limiting pH changes.

ISC Class 11 Chemistry · Equilibrium · Very Hard

17. A basic buffer commonly contains:

  • A. A strong base and strong acid
  • B. Only a weak acid
  • C. Only a neutral salt
  • D. A weak base and its salt with a strong acid
Answer: D
Explanation: A weak base and its conjugate acid form a basic buffer.

ISC Class 11 Chemistry · Equilibrium · Very Hard

18. At dynamic equilibrium in a reversible reaction:

  • A. Both reactions stop
  • B. Only the forward reaction continues
  • C. Forward and reverse reaction rates are equal
  • D. Reactant and product concentrations are equal
Answer: C
Explanation: Dynamic equilibrium means equal forward and reverse rates, not necessarily equal concentrations.

ISC Class 11 Chemistry · Equilibrium · Very Hard

19. The numerical value of an equilibrium constant changes primarily with:

  • A. Reaction vessel colour
  • B. Temperature
  • C. Catalyst concentration
  • D. Initial concentration alone
Answer: B
Explanation: For a specified reaction, K is a function of temperature.

ISC Class 11 Chemistry · Equilibrium · Very Hard

20. In a heterogeneous equilibrium, pure solids are generally:

  • A. Omitted from the equilibrium expression
  • B. Raised to zero concentration
  • C. Always placed in numerator
  • D. Treated as gases
Answer: A
Explanation: Activities of pure solids and pure liquids are effectively constant and absorbed into K.

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Equilibrium Practice Tests

Equilibrium Frequently Asked Questions

What is the difference between Q and K?

The reaction quotient Q uses the current composition; K describes the equilibrium composition at a fixed temperature. Comparing Q with K predicts the direction of shift.

Does a catalyst change the equilibrium constant?

No. A catalyst changes the rate at which equilibrium is reached but does not change the equilibrium constant at a given temperature.

How should I practise ionic equilibrium?

Work systematically with species, approximations, charge or mass balance when needed, and verify that the final concentration or pH is chemically reasonable.

Continue with another chapter to build connected concepts and strengthen your overall Chemistry preparation.

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