Question 71
In an elementary reaction, if two reactant molecules collide, the reaction is classified as:
A) Unimolecular
B) Bimolecular
C) Trimolecular
D) Zero-order
Answer: B) Bimolecular
Explanation: A bimolecular reaction involves the collision of two molecules in the rate-determining step.
Question 72
A catalyst works by:
A) Increasing the activation energy
B) Providing an alternative pathway with lower activation energy
C) Changing the equilibrium constant
D) Reacting with the products
Answer: B) Providing an alternative pathway with lower activation energy
Explanation: Catalysts lower the activation energy, allowing reactions to proceed more quickly without being consumed in the process.
Question 73
If a first-order reaction has a half-life of 10 minutes, what will be the concentration after 20 minutes?
A) Half of the initial concentration
B) One-fourth of the initial concentration
C) One-eighth of the initial concentration
D) One-sixteenth of the initial concentration
Answer: B) One-fourth of the initial concentration
Question 74
For the reaction 3A→B, the molecularity is:
A) 1
B) 2
C) 3
D) None of the above
Answer: C) 3
Explanation: The molecularity refers to the number of molecules involved in the reaction, so for this reaction, it is three (3A).
Question 75
The rate of a reaction is influenced by:
A) Concentration
B) Temperature
C) Presence of a catalyst
D) All of the above
Answer: D) All of the above
Explanation: All these factors can influence the rate of a chemical reaction.
Question 76
In the reaction mechanism, which of the following steps is usually the slowest?
A) Fast step
B) Rate-determining step
C) Catalytic step
D) Intermediate step
Answer: B) Rate-determining step
Explanation: The rate-determining step is the slowest step and limits the overall rate of the reaction.
Question 77
The overall order of the reaction is:
A) The sum of the molecularities of the reactants
B) The sum of the exponents in the rate law
C) The average of the exponents in the rate law
D) Always a whole number
Answer: B) The sum of the exponents in the rate law
Explanation: The overall order of the reaction is calculated by summing the powers of the concentrations in the rate law.
Question 78
For a reaction that is zero-order in respect to a reactant, what happens to the rate if the concentration is increased?
A) The rate increases.
B) The rate decreases.
C) The rate remains unchanged.
D) The rate becomes negative.
Answer: C) The rate remains unchanged.
Explanation: In a zero-order reaction, the rate is constant and does not depend on the concentration of the reactants.
Question 79
In a bimolecular reaction, if the concentration of one reactant is doubled, how does this affect the reaction rate?
A) The rate is unchanged.
B) The rate doubles.
C) The rate triples.
D) The rate quadruples.
Answer: B) The rate doubles.
Explanation: If the reaction is bimolecular and the concentration of one reactant is doubled, the reaction rate will double as well.
Question 80
The reaction 2A+B→C has a rate law of Rate=k[A]1[B]2 What is the order of the reaction with respect to A and B?
A) 1 for A and 2 for B
B) 2 for A and 1 for B
C) 1 for A and 3 for B
D) 3 for both
Answer: A) 1 for A and 2 for B
Explanation: The orders with respect to A and B are indicated by the exponents in the rate law.
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