MCQ 81:
Which of the following will NOT shift the equilibrium position of a reaction at equilibrium?
A) Changing the concentration of reactants
B) Adding a catalyst
C) Changing the temperature
D) Changing the pressure
Answer: B) Adding a catalyst
Explanation: A catalyst speeds up the rate of both the forward and reverse reactions equally but does not change the position of the equilibrium.
MCQ 82:
What happens to the reaction rate if the activation energy is decreased?
A) The reaction rate decreases.
B) The reaction rate remains the same.
C) The reaction rate increases.
D) The reaction rate becomes zero.
Answer: C) The reaction rate increases.
Explanation: Lowering the activation energy makes it easier for reactants to collide effectively, thus increasing the reaction rate.
MCQ 83:
In which of the following cases will the reaction rate be the fastest?
A) High concentration of reactants
B) Low temperature
C) High viscosity
D) Low pressure
Answer: A) High concentration of reactants
Explanation: Higher concentrations increase the frequency of collisions between reactant molecules, leading to a faster reaction rate.
MCQ 84:
The rate law expression for a reaction is determined experimentally. What does it indicate?
A) The overall energy change of the reaction
B) The stoichiometry of the balanced equation
C) The relationship between the rate of the reaction and the concentrations of reactants
D) The temperature dependence of the reaction
Answer: C) The relationship between the rate of the reaction and the concentrations of reactants
Explanation: The rate law provides insight into how the rate of a reaction depends on the concentration of reactants.
MCQ 85:
What is a characteristic of a reversible reaction?
A) It proceeds in one direction only.
B) It can reach a state of dynamic equilibrium.
C) It always produces gases.
D) It is always exothermic.
Answer: B) It can reach a state of dynamic equilibrium.
Explanation: Reversible reactions can go in both forward and reverse directions, allowing them to reach dynamic equilibrium.
MCQ 86:
Which of the following factors affects the equilibrium constant (K) for a given reaction?
A) The concentration of products
B) The temperature
C) The pressure
D) The presence of a catalyst
Answer: B) The temperature
Explanation: The equilibrium constant (K) changes with temperature; it is not affected by concentration changes or catalysts.
MCQ 87:
For a reaction that is second-order with respect to a reactant, which of the following is true?
A) Doubling the concentration of the reactant will quadruple the rate.
B) The rate is independent of the concentration.
C) The rate decreases with time.
D) The half-life is constant regardless of concentration.
Answer: A) Doubling the concentration of the reactant will quadruple the rate.
Explanation: In a second-order reaction, the rate is proportional to the square of the concentration; thus, doubling the concentration quadruples the rate.
MCQ 88:
If a reaction is exothermic, which of the following is true regarding the enthalpy change (ΔH)?
A) ΔH is positive.
B) ΔH is negative.
C) ΔH is zero.
D) ΔH varies with temperature.
Answer: B) ΔH is negative.
Explanation: In exothermic reactions, energy is released, resulting in a negative enthalpy change (ΔH).
MCQ 89:
In an endothermic reaction, if the temperature is increased, the equilibrium position will shift:
A) To the left
B) To the right
C) Remain unchanged
D) To the top
Answer: B) To the right
Explanation: For an endothermic reaction, increasing the temperature favors the formation of products, shifting the equilibrium position to the right.
MCQ 90:
What does it mean if a reaction is said to be at “dynamic equilibrium”?
A) No products or reactants are present.
B) The concentrations of reactants and products are equal.
C) The forward and reverse reactions occur at equal rates.
D) The reaction has stopped completely.
Answer: C) The forward and reverse reactions occur at equal rates.
Explanation: Dynamic equilibrium refers to a state where the rates of the forward and reverse reactions are equal, leading to constant concentrations of reactants and products.
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