Council for the Indian School Certificate Examinations (CISCE / ICSE / ISC) Class 11 Chemistry: Heterogeneous Equilibria

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

1. Heterogeneous Equilibria

   1.

   Which of the following describes a heterogeneous equilibrium?

   1. (A)

      The reaction involves only solid reactants.

   2. (B)

      All reactants and products are in the gaseous state.

   3. (C)

      All reactants and products are in the liquid state.

   4. (D)

      Reactants and products are in different physical states.

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   Answer: (D)

   Reactants and products are in different physical states.

   A heterogeneous equilibrium involves reactants and products existing in different physical states, such as solid and gas or liquid and gas.

   Heterogeneous Equilibria · Easy

2. 2.

   For the reaction $CaCO_3(s) \rightleftharpoons CaO(s) + CO_2(g)$, which expression correctly represents the equilibrium constant $K_p$?

   1. (A)

      $K_p = P_{CaCO_3} \times P_{CO_2}$

   2. (B)

      $K_p = P_{CO_2}$

   3. (C)

      $K_p = \frac{[CaO][CO_2]}{[CaCO_3]}$

   4. (D)

      $K_p = \frac{P_{CaO} \times P_{CO_2}}{P_{CaCO_3}}$

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   Answer: (B)

   $K_p = P_{CO_2}$

   In heterogeneous equilibria, the concentrations or partial pressures of pure solids and liquids are considered constant and are not included in the equilibrium constant expression. Thus, $K_p$ only depends on the partial pressure of $CO_2$.

   Heterogeneous Equilibria · Medium

3. 3.

   Consider the equilibrium $C(s) + H_2O(g) \rightleftharpoons CO(g) + H_2(g)$. If the amount of solid carbon is doubled, how will the equilibrium position be affected?

   1. (A)

      The equilibrium will shift to the left.

   2. (B)

      The equilibrium constant will decrease.

   3. (C)

      The equilibrium will shift to the right.

   4. (D)

      The equilibrium position will remain unchanged.

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   Answer: (D)

   The equilibrium position will remain unchanged.

   Changing the amount of a pure solid or liquid reactant or product does not affect the equilibrium position in a heterogeneous equilibrium, as their concentrations are constant and do not appear in the equilibrium constant expression.

   Heterogeneous Equilibria · Medium

4. 4.

   Assertion (A): The concentration of a pure solid or liquid is constant and does not appear in the equilibrium constant expression for a heterogeneous equilibrium.Reason (R): Pure solids and liquids have fixed densities, so their molar concentrations remain constant regardless of the amount present.

   1. (A)

      A is false but R is true.

   2. (B)

      A is true but R is false.

   3. (C)

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

   4. (D)

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

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   Answer: (D)

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

   Both the assertion and reason are correct, and the reason provides a valid explanation for why the concentrations of pure solids and liquids are excluded from the equilibrium constant expression.

   Heterogeneous Equilibria · Hard

5. 5.

   In a closed container, solid iodine ($I_2(s)$) sublimes to form iodine vapor ($I_2(g)$) at a constant temperature. Which of the following statements is true at equilibrium?

   1. (A)

      The rate of sublimation is greater than the rate of deposition.

   2. (B)

      The concentration of solid iodine continuously decreases.

   3. (C)

      The partial pressure of iodine vapor remains constant.

   4. (D)

      The total pressure inside the container continuously increases.

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   Answer: (C)

   The partial pressure of iodine vapor remains constant.

   At equilibrium in a physical heterogeneous equilibrium like sublimation, the rates of the forward and reverse processes are equal, leading to no net change in the macroscopic properties, including the partial pressure of the vapor.

   Heterogeneous Equilibria · Medium

— End of the paper · updated 8 October 2026 —