Important MCQs Related to LAW OF MASS ACTION and EQUILIBRIUM CONSTANT AND ITS UNITS || 10th chemistry
Q.1: What does the Law of Mass Action state?
A) The rate of a reaction is inversely proportional to its active mass.
B) The rate at which a substance reacts is directly proportional to its active mass.
C) The rate of reaction depends only on the products.
D) The rate of a reaction is constant.
Q.2: Who proposed the Law of Mass Action?
A) Dalton and Boyle
B) Guldberg and Waage
C) Avogadro and Gay-Lussac
D) Le Chatelier and Haber
Q.3: What is active mass considered as?
A) Mass of reactants in grams
B) Molar concentration in mol dm<sup>-3</sup>
C) Total mass of products
D) None of the above
Q.4: How is the equilibrium constant represented?
A) K
B) Kc
C) Kf
D) Kr
Q.5: What does Kf represent?
A) Rate constant for the reverse reaction
B) Rate constant for the forward reaction
C) Equilibrium constant
D) Concentration of reactants
Q.6: What happens at equilibrium?
A) The reaction stops completely.
B) The rate of the forward reaction equals the rate of the reverse reaction.
C) Only the forward reaction occurs.
D) The concentration of reactants increases.
Q.7: Which of the following is true about the equilibrium constant Kc?
A) It depends on the initial concentrations of reactants.
B) It remains constant at a given temperature.
C) It changes with pressure.
D) It has units in all cases.
Q.8: What is the equilibrium expression based on?
A) Mass of products only
B) Number of moles in the balanced equation
C) Temperature changes
D) Pressure changes
Q.9: How do you express the equilibrium constant for the reaction: A + B ⇌ C + D?
A) Kc = [A][B] / [C][D]
B) Kc = [C][D] / [A][B]
C) Kc = [A][C] / [B][D]
D) Kc = [B][D] / [A][C]
Q.10: What does a double arrow (⇌) indicate in a chemical reaction?
A) An irreversible reaction
B) A reaction that goes to completion
C) A reversible reaction
D) No reaction
Q.11: Which of the following does not affect the value of Kc?
A) Concentration of reactants
B) Temperature
C) Presence of a catalyst
D) Pressure of gases
Q.12: What is the unit of Kc if the number of moles of products equals the number of moles of reactants?
A) mol dm<sup>-3</sup>
B) No unit
C) mol<sup>2</sup> dm<sup>-6</sup>
D) dm<sup>3</sup>
Q.13: In the reaction H2 + I2 ⇌ 2HI, what is the expression for Kc?
A) Kc = [HI]<sup>2</sup> / [H2][I2]
B) Kc = [H2][I2] / [HI]<sup>2</sup>
C) Kc = [I2] / [H2]
D) Kc = [HI] / [H2]
Q.14: Which statement is true about dynamic equilibrium?
A) All reactions stop.
B) The rates of forward and reverse reactions are equal.
C) Only the forward reaction occurs.
D) Concentrations of products only change.
Q.15: When the concentration of reactants decreases, what happens to the rate of the forward reaction?
A) It increases.
B) It decreases.
C) It remains the same.
D) It stops.
Q.16: What is the equilibrium constant expression for the reaction 2A ⇌ B + C?
A) Kc = [A]<sup>2</sup> / [B][C]
B) Kc = [B][C] / [A]<sup>2</sup>
C) Kc = [C] / [B][A]
D) Kc = [A] / [B][C]
Q.17: If the concentration of products increases, what happens to the rate of the reverse reaction?
A) It increases.
B) It decreases.
C) It remains the same.
D) It stops.
Q.18: What happens to Kc if the temperature increases for an exothermic reaction?
A) Kc increases.
B) Kc decreases.
C) Kc remains the same.
D) Kc becomes zero.
Q.19: In which system does equilibrium occur?
A) Open system
B) Closed system
C) Isolated system
D) Any system
Q.20: What happens to the concentrations of reactants and products at equilibrium?
A) They both increase indefinitely.
B) They both decrease indefinitely.
C) They remain constant.
D) They fluctuate wildly.
Q.21: What is the unit of Kc when the moles of products are greater than moles of reactants?
A) No unit
B) mol dm<sup>-3</sup>
C) mol<sup>2</sup> dm<sup>-6</sup>
D) dm<sup>3</sup>
Q.22: How is the equilibrium constant affected by a catalyst?
A) It increases.
B) It decreases.
C) It remains unchanged.
D) It becomes zero.
Q.23: In the reaction N2 + 3H2 ⇌ 2NH3, what is the expression for Kc?
A) Kc = [NH3]<sup>2</sup> / [N2][H2]<sup>3</sup>
B) Kc = [N2][H2]<sup>3</sup> / [NH3]<sup>2</sup>
C) Kc = [NH3] / [N2][H2]
D) Kc = [N2] / [H2]<sup>3</sup>
Q.24: What is the equilibrium expression for the reaction H2 + I2 ⇌ 2HI?
A) Kc = [HI]<sup>2</sup> / [H2][I2]
B) Kc = [H2][I2] / [HI]<sup>2</sup>
C) Kc = [I2] / [H2]
D) Kc = [HI] / [H2]
Q.25: What does it mean when Kc is greater than 1?
A) Products are favored at equilibrium.
B) Reactants are favored at equilibrium.
C) No reaction occurs.
D) Reaction goes to completion.
Q.26: What does it mean when Kc is less than 1?
A) Products are favored at equilibrium.
B) Reactants are favored at equilibrium.
C) No reaction occurs.
D) Reaction goes to completion.
Q.27: What happens to equilibrium when the concentration of a reactant is increased?
A) The equilibrium shifts towards products.
B) The equilibrium shifts towards reactants.
C) The equilibrium does not shift.
D) The reaction stops.
Q.28: What is represented by the square brackets [ ] in chemical expressions?
A) Temperature
B) Active mass (molar concentration)
C) Pressure
D) Volume
Q.29: Which of the following reactions is reversible?
A) Combustion of fuels
B) Rusting of iron
C) Dissolution of sugar in water
D) Formation of water from hydrogen and oxygen
Q.30: What is a characteristic of a closed system in terms of equilibrium?
A) Substances can escape.
B) No substances can enter or leave.
C) Only reactants are present.
D) The reaction occurs slowly.
CORRECT ANSWER