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

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

1. Homogeneous Equilibria

   1.

   For the homogeneous reaction $2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$, which of the following expressions correctly represents the equilibrium constant $K_c$?

   1. (A)

      $K_c = \frac{[SO_2]^2[O_2]}{[SO_3]^2}$

   2. (B)

      $K_c = \frac{2[SO_3]}{2[SO_2][O_2]}$

   3. (C)

      $K_c = \frac{[SO_3]}{[SO_2][O_2]}$

   4. (D)

      $K_c = \frac{[SO_3]^2}{[SO_2]^2[O_2]}$

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   Answer: (D)

   $K_c = \frac{[SO_3]^2}{[SO_2]^2[O_2]}$

   The equilibrium constant $K_c$ is defined as the ratio of the product of the molar concentrations of products to the product of the molar concentrations of reactants, each raised to the power of their stoichiometric coefficients.

   Homogeneous Equilibria · Easy

2. 2.

   Consider the reaction $H_2(g) + I_2(g) \rightleftharpoons 2HI(g)$. If the reaction is carried out in a closed vessel, how does the equilibrium constant $K_p$ relate to $K_c$?

   1. (A)

      $K_p = K_c(RT)^2$

   2. (B)

      $K_p = K_c$

   3. (C)

      $K_p = K_c/(RT)$

   4. (D)

      $K_p = K_c(RT)$

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   Answer: (B)

   $K_p = K_c$

   For the given reaction, the change in the number of moles of gas, $\Delta n_g = (2) - (1+1) = 0$. Since $K_p = K_c(RT)^{\Delta n_g}$, when $\Delta n_g = 0$, then $K_p = K_c(RT)^0 = K_c$.

   Homogeneous Equilibria · Medium

3. 3.

   Assertion (A): All reactants and products in a homogeneous equilibrium are in the same physical state.Reason (R): In homogeneous equilibrium, the equilibrium constant can be expressed using either concentrations ($K_c$) or partial pressures ($K_p$).

   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: (B)

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

   Assertion (A) is true by definition of homogeneous equilibrium. Reason (R) is also true, as both $K_c$ and $K_p$ are valid ways to express equilibrium constants for gaseous homogeneous reactions. However, R does not explain why A is true; it describes a consequence of the nature of homogeneous equilibria.

   Homogeneous Equilibria · Medium

4. 4.

   For a homogeneous equilibrium, if the reaction is exothermic in the forward direction, how will an increase in temperature affect the value of the equilibrium constant $K_c$?

   1. (A)

      $K_c$ will decrease.

   2. (B)

      The effect on $K_c$ cannot be determined without more information.

   3. (C)

      $K_c$ will remain unchanged.

   4. (D)

      $K_c$ will increase.

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   Answer: (A)

   $K_c$ will decrease.

   For an exothermic reaction, an increase in temperature shifts the equilibrium to the left (towards reactants) to absorb the added heat, thus decreasing the concentration of products and increasing the concentration of reactants, which results in a decrease in the value of $K_c$.

   Homogeneous Equilibria · Hard

5. 5.

   Consider the reaction $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$ occurring in a sealed container. Initially, 1 mole of $N_2$ and 3 moles of $H_2$ are mixed. At equilibrium, 0.5 moles of $NH_3$ are formed. If the total volume is 1 L, what is the equilibrium concentration of $N_2$?

   1. (A)

      0.25 M

   2. (B)

      0.5 M

   3. (C)

      1.0 M

   4. (D)

      0.75 M

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   Answer: (D)

   0.75 M

   From the stoichiometry, 0.5 moles of $NH_3$ formed means 0.25 moles of $N_2$ reacted (since 2 moles $NH_3$ require 1 mole $N_2$). Initial $N_2$ was 1 mole. So, equilibrium $N_2 = 1 - 0.25 = 0.75$ moles. Since volume is 1 L, the concentration is 0.75 M.

   Homogeneous Equilibria · Hard

— End of the paper · updated 8 October 2026 —