MCQ 41:
A reaction where the rate decreases as the reaction proceeds is typically:
A) First-order
B) Second-order
C) Zero-order
D) A pseudo-first-order reaction
Answer: A) First-order
Explanation: In a first-order reaction, the rate decreases as the concentration of the reactant decreases over time.
MCQ 42:
Which of the following factors is least likely to influence the rate of a reaction involving solid reactants?
A) Surface area
B) Temperature
C) Presence of a catalyst
D) Color of the reactants
Answer: D) Color of the reactants
Explanation: The color of solid reactants does not affect the rate of the reaction, while surface area, temperature, and catalysts do have significant impacts.
MCQ 43:
In a reaction mechanism, the elementary steps are:
A) Single events that occur in a multi-step reaction.
B) The overall reaction.
C) Irreversible by nature.
D) Not influenced by catalysts.
Answer: A) Single events that occur in a multi-step reaction.
Explanation: Elementary steps are individual steps in a reaction mechanism that describe distinct changes in reactants to products.
MCQ 44:
The transition state of a reaction is best described as:
A) The final product of the reaction.
B) A high-energy state during the reaction.
C) The starting material.
D) An intermediate product.
Answer: B) A high-energy state during the reaction.
Explanation: The transition state is a temporary, high-energy state that occurs during the conversion of reactants to products.
MCQ 45:
Which of the following statements about reaction rates is correct?
A) All reactions occur at the same rate.
B) Reaction rates can be influenced by temperature and concentration.
C) Increasing the activation energy decreases the reaction rate.
D) Catalysts decrease the rate of reaction.
Answer: B) Reaction rates can be influenced by temperature and concentration.
Explanation: Reaction rates are affected by several factors, including temperature, concentration of reactants, and the presence of catalysts.
MCQ 46:
The rate of a reaction is doubled by doubling the concentration of a reactant. What is the order of the reaction with respect to that reactant?
A) Zero-order
B) First-order
C) Second-order
D) Third-order
Answer: B) First-order
Explanation: If doubling the concentration of a reactant doubles the rate of reaction, it indicates a first-order dependence on that reactant.
MCQ 47:
In a reaction where the rate is unaffected by changes in concentration, the reaction is classified as:
A) Zero-order
B) First-order
C) Second-order
D) Pseudo-first-order
Answer: A) Zero-order
Explanation: A zero-order reaction exhibits a constant rate that does not depend on the concentration of reactants.
MCQ 48:
What does the rate constant (k) indicate about a reaction?
A) The concentration of products at equilibrium
B) The speed of the reaction under specific conditions
C) The amount of energy released
D) The nature of the reactants
Answer: B) The speed of the reaction under specific conditions
Explanation: The rate constant (k) is a proportionality constant that relates the rate of reaction to the concentration of reactants at a given temperature.
MCQ 49:
If a catalyst increases the rate of reaction, what happens to the activation energy?
A) It increases.
B) It decreases.
C) It remains the same.
D) It becomes negative.
Answer: B) It decreases.
Explanation: A catalyst lowers the activation energy required for a reaction, allowing it to proceed more quickly.
MCQ 50:
Which of the following conditions is necessary for a successful collision between reactant molecules?
A) High pressure
B) Sufficient energy and proper orientation
C) Low temperature
D) High concentration
Answer: B) Sufficient energy and proper orientation
Explanation: For a collision to result in a reaction, molecules must collide with sufficient energy and in the correct orientation to break bonds and form new products.
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