Equilibria MCQs PDF

1. Which of the following best de nes dynamic equilibrium? a) The forward reaction stops b) The rate of the forward reaction equals the rate of the reverse reaction c) Only the forward reaction occurs d) The concentrations of reactants increase...

1. Which of the following best de nes dynamic equilibrium? a) The forward reaction stops b) The rate of the forward reaction equals the rate of the reverse reaction c) Only the forward reaction occurs d) The concentrations of reactants increase Answer: b) The rate of the forward reaction equals the rate of the reverse reaction Explanation: Dynamic equilibrium is reached when the rates of the forward and reverse reactions are equal, and concentrations of reactants and products remain constant. 2. What happens when equilibrium is reached in a reversible reaction? a) The reactant concentration keeps increasing b) The product concentration keeps increasing c) Both reactants and products' concentrations remain constant d) The reaction stops completely Answer: c) Both reactants and products' concentrations remain constant Explanation: At equilibrium, the concentrations of reactants and products remain constant as the rate of the forward reaction equals the rate of the reverse reaction. 3. According to Le Chatelier's principle, what happens if the concentration of a reactant is increased? a) The equilibrium shifts to produce more products b) The equilibrium shifts to produce more reactants c) The equilibrium remains unchanged d) The reaction stops Answer: a) The equilibrium shifts to produce more products Explanation: Le Chatelier's principle states that if the concentration of a reactant is increased, the equilibrium shifts to counteract this change by producing more products. 4. Which conditions would favour the forward reaction in an exothermic reaction? a) Decrease temperature and decrease pressure b) Increase temperature and increase pressure c) Decrease temperature and increase pressure d) Increase temperature and decrease pressure Answer: c) Decrease temperature and increase pressure Explanation: Exothermic reactions release heat, so decreasing temperature favours the forward reaction. Increasing pressure would also favour the side with fewer moles of gas. 5. What e ect does adding a catalyst have on the position of equilibrium? a) Shifts the equilibrium to the right b) Shifts the equilibrium to the left c) Has no e ect on the equilibrium position d) Increases the amount of products Answer: c) Has no e ect on the equilibrium position Explanation: A catalyst speeds up both the forward and reverse reactions equally, hence it does not a ect the position of equilibrium. 6. What is the expression for the equilibrium constant (Kc) for the reaction \( aA + bB ⇌ cC + dD \)? a) \[ \frac{[A]^a [B]^b}{[C]^c [D]^d} \] b) \[ [A]^a [B]^b \] c) \[ \frac{[C]^c [D]^d}{[A]^a [B]^b} \] d) \[ [C]^c [D]^d \] ff ff ff ff fi  Answer: c) \[ \frac{[C]^c [D]^d}{[A]^a [B]^b} \] Explanation: The equilibrium constant, Kc, is expressed in terms of the concentrations of the products and reactants each raised to the power of their coe cients in the balanced equation. 7. In a dynamic equilibrium, how does temperature change a ect the value of Kc? a) Only increases b) Only decreases c) Remains constant d) Depends on the reaction's enthalpy change Answer: d) Depends on the reaction's enthalpy change Explanation: For endothermic reactions, increasing the temperature increases Kc, while for exothermic reactions, increasing the temperature decreases Kc. 8. Which principle predicts the shift in equilibrium when pressure is increased in a gaseous system? a) Hess's Law b) Le Chatelier's Principle c) Dalton's Law d) Avogadro's Law Answer: b) Le Chatelier's Principle Explanation: Le Chatelier's Principle explains how the equilibrium position shifts to counteract changes in concentration, temperature, and pressure. 9. According to Le Chatelier's principle, what happens in an endothermic reaction if the temperature is increased? a) Equilibrium shifts to the left b) Equilibrium shifts to the right c) Equilibrium remains unchanged d) Reaction speed increases without equilibrium shift Answer: b) Equilibrium shifts to the right Explanation: For endothermic reactions, increasing the temperature supplies additional energy, shifting the equilibrium to the right to absorb the added heat. 10. Calculate the value of Kc for the reaction \( N_2 + 3H_2 ⇌ 2NH_3 \) given the equilibrium concentrations: [N₂] = 0.2 M, [H₂] = 0.5 M, [NH₃] = 0.4 M. a) 0.128 b) 4.0 c) 0.8 d) 1.28 Answer: b) 4.0 Explanation: Kc = \[ \frac{[NH₃]^2}{[N₂][H₂]^3} \] = \[ \frac{(0.4)^2}{(0.2)(0.5)^3} \] = \[ \frac{0.16} {0.025} \] = 4.0. 11. Which direction will the equilibrium shift if the volume of the reaction vessel is decreased for the reaction \( N₂(g) + 3H₂(g) ⇌ 2NH₃(g) \)? a) To the right b) To the left c) No shift d) Randomly shifts Answer: a) To the right Explanation: Decreasing volume increases pressure, and the system shifts towards the side with fewer gas moles. Here, it shifts to the right producing fewer gas molecules (2NH₃ versus 4 reactants). ff ffi  12. What does a Kc value greater than 1 indicate about the position of equilibrium? a) Equilibrium favours the reactants b) Equilibrium favours the products c) Equilibrium lies perfectly in the middle d) Reaction is non-reversible Answer: b) Equilibrium favours the products Explanation: If Kc > 1, the equilibrium lies to the right, favouring the formation of products. 13. For the reaction \( 2SO₂ + O₂ ⇌ 2SO₃ \), what is the e ect of increasing pressure on the yield of SO₃? a) Increases b) Decreases c) Remains constant d) Depends on catalyst presence Answer: a) Increases Explanation: Increasing pressure favours the side with fewer gas moles. There are fewer moles of gas on the product side (2 moles of SO₃) than on the reactant side (3 moles; 2SO₂ + O₂). 14. Why is the value of Kc una ected by the presence of a catalyst? a) Catalyst reacts with reactants b) Catalyst changes the number of moles c) Catalyst speeds up reaction rates equally d) Catalyst alters the equilibrium concentration Answer: c) Catalyst speeds up reaction rates equally Explanation: A catalyst increases the rates of both the forward and reverse reactions equally, thus it does not a ect the equilibrium position or Kc value. 15. In the reaction: \( PCl₅ ⇌ PCl₃ + Cl₂ \), what e ect does increasing the concentration of Cl₂ have on the equilibrium? a) Shifts to the right b) Shifts to the left c) No e ect d) Increases Cl₂ concentration only Answer: b) Shifts to the left Explanation: Le Chatelier's principle states that increasing the concentration of a product will shift the equilibrium to the left to decrease the added product's concentration. 16. Which equilibrium expression is correct for \( 2NO₂ ⇌ N₂O₄ \)? a) Kc = \[ \frac{[NO₂]^2}{[N₂O₄]} \] b) Kc = \[ \frac{[N₂O₄]}{[NO₂]^2} \] c) Kc = \[ \frac{[N₂O₄]^2}{[NO₂]} \] d) Kc = \[ \frac{[NO₂]}{[N₂O₄]^2} \] Answer: b) Kc = \[ \frac{[N₂O₄]}{[NO₂]^2} \] Explanation: Kc is calculated using the concentrations of products over reactants each raised to their respective coe cients in the balanced equation. 17. For the reaction \( CO + 2H₂ ⇌ CH₃OH \), if the pressure is increased, what happens? a) Yield of CO increases b) Yield of CH₃OH increases c) No change in yield d) Reaction stops ff ff ffi ff ff ff  Answer: b) Yield of CH₃OH increases Explanation: Increasing pressure favours the side with fewer gas molecules, here the right side with one mole of CH₃OH versus 3 moles of reactants. 18. Calculate the concentration of \( H_2 \) at equilibrium if \( K_{c} \) is given for the reaction \ ( N_2 + 3H_2 ⇌ 2NH_3 \) with equilibrium concentrations \([ N_2 ] = 0.5 \, mol/dm^3 \), \([ NH_3] = 2.0 \, mol/dm^3 \). a) 0.25 b) 1.5 c) 2.0 d) 3.0 Answer: d) 3.0 Explanation: Use Kc to nd \([ H_2] \). Kc = \([ NH_3]^2 / ([N_2][H_2]^3)\). Rearrange to nd \ ([H_2]\). Careful substitution and solving achieves this solution. 19. Which principle is used to predict the outcome of changing conditions for equilibrium reactions in industry? a) Dalton's Law b) Boyle's Law c) Bohr's Principle d) Le Chatelier's Principle Answer: d) Le Chatelier's Principle Explanation: Le Chatelier's Principle is applied to predict how changes in concentration, temperature, and pressure will in uence equilibrium positions in industrial reactions】. 20. In the exothermic reaction \( 2SO₂ + O₂ ⇌ 2SO₃ \), how does reducing the temperature a ect the equilibrium? a) Increases SO₃ production b) Decreases SO₃ production c) No e ect d) Increases SO₂ production Answer: a) Increases SO₃ production Explanation: For exothermic reactions, reducing temperature favours the forward reaction, hence increasing the output of SO₃. 21. Given Kc < 1, which side is favoured in the reaction at equilibrium? a) Product side b) Reactant side c) Neither side d) Both sides equally Answer: b) Reactant side Explanation: Kc less than 1 signi es that the equilibrium favours the reactants, leading to a higher concentration of reactants than products at equilibrium. 22. How do catalysts a ect Le Chatelier's principle? a) Shifts equilibrium right b) Shifts equilibrium left c) A ects yield but not equilibrium d) No e ect Answer: d) No e ect Explanation: Catalysts increase rates for both the forward and reverse reactions equally, establishing equilibrium faster but without shifting its position. 23. What is the e ect of decreasing the concentration of products in a dynamic equilibrium? ff ff ff ff ff ff fi fl fi fi ff  a) Shifts equilibrium to the right b) Shifts equilibrium to the left c) No change d) Slows down the reaction Answer: a) Shifts equilibrium to the right Explanation: Decreasing product concentration causes the equilibrium to shift right to produce more products compensating for the decrease. 24. For \( H₂ + I₂ ⇌ 2HI \), what happens when the pressure is increased? a) Equilibrium shifts to left b) Equilibrium shifts to right c) No e ect d) Reaction pauses Answer: c) No e ect Explanation: The number of gas moles on both sides of the equation is equal (2 moles each side), so changes in pressure have no e ect on the equilibrium shift. 25. What is meant by equilibrium position? a) Concentration of catalysts b) Pressure within reaction vessel c) Relative amounts of reactants and products d) Net reaction energy Answer: c) Relative amounts of reactants and products Explanation: The equilibrium position refers to the ratio of concentrations of reactants and products once equilibrium is established. 26. What e ect does removing reactants have on equilibrium in \( A + B ⇌ C + D \)? a) Shifts right b) Shifts left c) No e ect d) Equilibrium halts Answer: b) Shifts left Explanation: According to Le Chatelier’s principle, removing reactants shifts equilibrium to left attempting to replace the removed reactants. 27. What is the relationship between temperature changes and Kc in exothermic reactions? a) Increasing temperature decreases Kc b) Increasing temperature increases Kc c) Temperature has no e ect d) Temperature change only a ects product concentration Answer: a) Increasing temperature decreases Kc Explanation: For exothermic reactions, temperature increase provides heat shifting equilibrium left, decreasing the value of Kc. 28. What is the unit of the equilibrium constant (Kc) for the reaction \( 2NO₂ ⇌ N₂O₄ \)? a) mol^3 dm^-3 b) dm^3 mol^-1 c) mol dm^-3 d) no unit Answer: b) dm^3 mol^-1 Explanation: This reaction's Kc units are calculated based on the ratio of product to reactant concentrations raised to their coe cients in the equation. ff ff ff ff ff ff ffi ff 29. For the reaction \( 2SO₂ + O₂ ⇌ 2SO₃ \) how is Kc calculated from given concentrations? a) \[ \frac{[SO₃]^2}{[SO₂]^2[O₂]} \] b) \[ \frac{[SO₂][O₂]}{[SO₃]^2} \] c) \[ \frac{[SO₂]^2[O₂]}{[SO₃]^2} \] d) \[ \frac{[SO₃]}{[SO₂][O₂]} \] Answer: a) \[ \frac{[SO₃]^2}{[SO₂]^2[O₂]} \] Explanation: Kc is determined using the concentrations of products over reactants raised to the power of their stoichiometric coe cients. ffi