practice equilibrium questions and answers in chemistry

Q.1. Mention the factors that affect equilibrium constant.

• Answer 1:Temperature, pressure, catalyst and molar concentration of reactants and products.

Q.2. Write relationship between K_p and K_c for the gaseous reaction: N₂ + O₂ ⇌ 2NO

• Answer 2: K_p = K_c as Δn is zero for the above said reaction.

Q.3. Write Kc for the gaseous reaction: N₂ + 3H₂ ⇌ 2NH₃

• Answer 3: K_c = [𝑁𝐻₃]² /[𝑁₂] [𝐻₂]³

Q.4. What is effect of catalyst on equilibrium constant K_c?

• Answer 4: A catalyst does not affect equilibrium constant because it speeds up both forward and backward reactions to the same extent.

Q.5. State Le Chatelier’s principle.

• Answer 5: It states that a change in any of the factors that determine the equilibrium conditions of a system will cause the system to change in such a manner so as to reduce or to counteract the effect of the change.

Q.6. Explain homogeneous and heterogeneous equilibrium giving examples.

• Answer 6: If all the reactants and products present in an equilibrium mixture are in same phase → homogeneous equilibrium.
  Example: 𝑁₂(𝑔) + 3𝐻₂ (𝑔) ⇌ 2𝑁𝐻₃ (𝑔)
  If all the reactants and products present in an equilibrium mixture are indifferent phase → heterogeneous equilibrium.
  Example: 𝐶𝑎𝐶𝑂₃ (𝑠) ⇌ 𝐶𝑎𝑂(𝑠) +𝐶𝑂₂(𝑔)

Q.7. Describe the effect of a) addition of H₂
b) addition of CH₃OH
c) removal of CO
d) removal of CH₃OH on the equilibrium of the reaction: 2H₂ (g) + CO (g ) ⇌ CH₃OH (g)

• Answer 7: a) addition of H₂ equilibrium will shift on RHS.
  b) addition of CH₂OH equilibrium will shift on LHS.
  c) removal of CO equilibrium will shift on LHS.
  d) removal of CH₃OH equilibrium will shift on RHS.
  

Q.8. For the equilibrium, 2NOCl(g) ⇌ 2NO(g) + Cl₂(g) the value of the equilibrium constant, K_c is 3.75×10^–6 at 1069 K. Calculate the K_p for the reaction at this temperature?

• Answer 8: We know that, K_p = K_c (RT)^Δn
  For the above reaction,
  Δn = (2+1) – 2 = 1
  Using, K_p = K_c (RT)^Δn
  Kp = 3.75 ×10–6 (0.0831 × 1069)
  Kp = 0.033.
  

Q.9. Hydrolysis of sucrose gives, Sucrose + H₂O → Glucose + Fructose
Equilibrium constant K_c for the reaction is 2 × 10¹³ at 300 K. Calculate ΔG⁰ at 300 K.

• Answer 9: ΔG⁰ = – RT lnK_c
  ΔG⁰ = – 8.314 × 300 × ln( 2×10₁₃ )
  ΔG⁰ = – 7.64 ×104 J/mol.
  

Q.10. At 473 K, equilibrium constant Kc for decomposition of phosphorus pentachloride, PCl₅ is 8.3 ×10^–3.
If decomposition is depicted as, PCl₅ (g) ⇌ PCl₃(g) + Cl₂ (g) Δ_rH⁰ = 124.0 kJ mol–1
a) Write an expression for Kc for the reaction.
b) What is the value of K_c for the reverse reaction at the same temperature?
c) What would be the effect on K_c if
(i) more PCl₅is added
(ii) pressure is increased
(iii) the temperature is increased ?

• Answer 10: a) 𝐾_c=[𝑃𝐶𝑙₃][𝐶𝑙₂][𝑃𝐶𝑙₅] b) 120.48 c) (i) equilibrium will shift on RHS.
  (ii) equilibrium will shift on LHS.
  (iii) equilibrium will shift on RHS.
  

Q.11. Dihydrogen gas is obtained from natural gas by partial oxidation with steam As per following endothermic reaction:
CH₄ (g) + H₂O (g) ⇌ CO (g) + 3H₂ (g)
(a) Write as expression for K_p for the above reaction.
(b) How will the values of K_p and composition of equilibrium mixture be Affected by
(i) increasing the pressure
(ii) increasing the temperature
(iii) using a catalyst?

• Answer 11: (a) 𝐾_𝑝=[𝐶𝑂][𝐻₂]³/[𝐶𝐻₄][𝐻₂𝑂]
  (b) (i) Value of K_p will not change, equilibrium will shift in backward direction.
  (ii) Value of K_p will increase and reaction will proceed in forward direction.
  (iii) No effect.