Equilibrium Constant Kc and Kp - UNSOLVED PRACTICE SET

Q7. Write the expressions for Kc and Kp for the reaction: 2NO(g) + O₂(g) ⇌ 2NO₂(g). What are the units of Kc and Kp for this reaction?

Q8. For the reaction H₂(g) + I₂(g) ⇌ 2HI(g), Kc = 54.3 at 700 K. What does this value tell you about the position of equilibrium? Does Kc have units in this case?

Q9. Explain why the equilibrium constant has a fixed value at a given temperature, even though the initial concentrations of reactants may vary.

Q10. A reaction has Kc = 1.0 × 10⁻⁵ at 298 K. Is the forward reaction favoured at this temperature? Explain your answer.

Q11. For the decomposition of PCl₅: PCl₅(g) ⇌ PCl₃(g) + Cl₂(g), write expressions for Kc and Kp. How are they related?

Q12. Can the equilibrium constant Kc ever be negative? Explain with reasoning.

Section C: Long Answer Questions

Q13. (a) Define equilibrium constant Kc and Kp. For what type of reactions is Kp used instead of Kc?

(b) Derive the relationship between Kp and Kc for a general gaseous reaction.

(c) For the reaction N₂(g) + O₂(g) ⇌ 2NO(g), Kp = 4.0 × 10⁻⁴ at 2000 K. Calculate Kc at the same temperature. (R = 0.0821 L·atm/K·mol)

Q14. (a) Explain the significance of the magnitude of the equilibrium constant. How does the value of K help predict the extent of a reaction?

(b) For the reaction: H₂(g) + CO₂(g) ⇌ H₂O(g) + CO(g), Kc = 4.40 at 2000 K. In a 2.0 L container, 0.20 mol of H₂ and 0.20 mol of CO₂ are mixed. Calculate the equilibrium concentrations of all species.

(c) What happens to the value of Kc if a catalyst is added to the system? Explain.

Q15. (a) Explain why the equilibrium constant is independent of:

(i) Initial concentrations

(ii) Presence of a catalyst

(iii) Pressure (for reactions where Δn = 0)

(b) For the reaction: 2NO₂(g) ⇌ N₂O₄(g), Kp = 6.8 at 298 K. Calculate Kc for this reaction.

(c) A student claims that if the volume of the container is doubled, the value of Kc will decrease by half. Is the student correct? Explain your answer.

Q16. For the reaction: CO(g) + H₂O(g) ⇌ CO₂(g) + H₂(g)

At 700 K, Kc = 5.10. Initially, 1.00 mol of CO and 1.00 mol of H₂O are placed in a 2.00 L container.

(a) Set up an ICE table for this equilibrium.

(b) Calculate the equilibrium concentrations of all species.

(c) Calculate the value of Kp at 700 K.

(d) What percentage of CO has been converted to CO₂ at equilibrium?

Q17. The dissociation of phosphorus pentachloride is given by:

PCl₅(g) ⇌ PCl₃(g) + Cl₂(g)

At 250°C, Kp = 1.80 atm.

(a) Calculate Kc for this reaction at 250°C.

(b) If 0.20 mol of PCl₅ is placed in a 1.0 L flask, calculate the degree of dissociation (α) at equilibrium.

(c) Calculate the partial pressures of all species at equilibrium.

(R = 0.0821 L·atm/K·mol)

Q18. In India, the production of ammonia via the Haber process is crucial for fertiliser manufacturing:

N₂(g) + 3H₂(g) ⇌ 2NH₃(g)

At 500 K, Kp = 1.5 × 10⁻⁵.

(a) Calculate Kc at 500 K.

(b) In an industrial reactor, the initial partial pressures are: P_N₂ = 50 atm, P_H₂ = 150 atm, P_NH₃ = 0. Calculate the equilibrium partial pressure of NH₃ if the total pressure is maintained at 200 atm.

(c) The industrial process operates at 450-500°C and 200 atm. Explain why a compromise temperature is chosen, considering both thermodynamic (Kp) and kinetic factors.

(d) A student suggests operating at 800 K to increase the reaction rate. What would happen to the equilibrium yield of ammonia? Calculate Kc at 800 K if Kp = 2.5 × 10⁻⁷ at this temperature, and comment on the feasibility.