Council for the Indian School Certificate Examinations (CISCE / ICSE / ISC) Class 11 Chemistry: Equilibrium in Physical and Chemical Processes

Instructions. Answer all questions. Fill exactly one bubble per question on the OMR sheet.

1. Equilibrium in Physical and Chemical Processes

   1.

   Assertion (A): A system at equilibrium is dynamic.Reason (R): At equilibrium, the rates of forward and reverse reactions are equal, leading to no net change in concentrations.

   1. (A)

      A is true but R is false.

   2. (B)

      Both A and R are true but R is not the correct explanation of A.

   3. (C)

      Both A and R are true and R is the correct explanation of A.

   4. (D)

      A is false but R is true.

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   Answer: (C)

   Both A and R are true and R is the correct explanation of A.

   At equilibrium, reactions are still occurring but the forward and reverse rates are equal, meaning there is constant microscopic activity without any observable macroscopic change, confirming the dynamic nature explained by the equal rates.

   Equilibrium in Physical and Chemical Processes · Medium

2. 2.

   Which of the following describes a system in physical equilibrium?

   1. (A)

      Water vaporizing from a liquid at its boiling point in an open container.

   2. (B)

      Ice melting in a closed container at $0^ ext{o}C$ and 1 atm pressure.

   3. (C)

      The reaction between hydrogen and iodine to form hydrogen iodide.

   4. (D)

      The decomposition of calcium carbonate in a closed vessel.

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   Answer: (B)

   Ice melting in a closed container at $0^ ext{o}C$ and 1 atm pressure.

   Physical equilibrium involves a balance between two physical states of the same substance, such as solid and liquid water at $0^ ext{o}C$, where the rate of melting equals the rate of freezing.

   Equilibrium in Physical and Chemical Processes · Easy

3. 3.

   Consider a saturated solution of salt. If more salt is added, it does not dissolve. This indicates that the system has reached:

   1. (A)

      Dynamic equilibrium

   2. (B)

      Kinetic equilibrium

   3. (C)

      Static equilibrium

   4. (D)

      Chemical equilibrium

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   Answer: (A)

   Dynamic equilibrium

   A saturated solution is an example of dynamic equilibrium where the rate of dissolution of the solid equals the rate of crystallization, even though there's no net change in the amount of dissolved solute.

   Equilibrium in Physical and Chemical Processes · Medium

4. 4.

   When a chemical reaction reaches equilibrium, which statement is true?

   1. (A)

      The reverse reaction stops.

   2. (B)

      The concentrations of reactants and products become zero.

   3. (C)

      The rate of the forward reaction equals the rate of the reverse reaction.

   4. (D)

      The forward reaction stops.

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   Answer: (C)

   The rate of the forward reaction equals the rate of the reverse reaction.

   At chemical equilibrium, the forward and reverse reactions continue to occur, but their rates become equal, resulting in no net change in the concentrations of reactants and products over time.

   Equilibrium in Physical and Chemical Processes · Easy

5. 5.

   A sealed bottle of soda water contains dissolved carbon dioxide gas in equilibrium with carbon dioxide gas above the liquid. What happens when the bottle is opened?

   1. (A)

      The rate of carbon dioxide escaping from the liquid increases.

   2. (B)

      The system reaches a new equilibrium with less dissolved carbon dioxide.

   3. (C)

      The equilibrium shifts towards more dissolved carbon dioxide.

   4. (D)

      The pressure of carbon dioxide gas above the liquid increases.

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   Answer: (A)

   The rate of carbon dioxide escaping from the liquid increases.

   When the bottle is opened, the external pressure of carbon dioxide decreases significantly. This causes the rate of carbon dioxide escaping from the liquid to increase, as the system tries to re-establish equilibrium under the new, lower external pressure.

   Equilibrium in Physical and Chemical Processes · Hard

— End of the paper · updated 8 October 2026 —