Question 21
If the rate of a reaction quadruples when the concentration of one reactant is doubled, what is the order of the reaction with respect to that reactant?
A) 1
B) 2
C) 3
D) 4
Answer: B) 2
Explanation: If doubling the concentration of a reactant results in a fourfold increase in the rate, the reaction is second order with respect to that reactant, since (22)=4
Question 22
In a first-order reaction, which of the following is true?
A) The half-life is dependent on the initial concentration.
B) The half-life is constant and independent of concentration.
C) The rate decreases linearly with time.
D) The reaction must have a catalyst to proceed.
Answer: B) The half-life is constant and independent of concentration.
Explanation: In first-order reactions, the half-life remains constant regardless of the initial concentration of the reactants.
Question 23
A reaction has a molecularity of 1. This means the reaction is:
A) Bimolecular
B) Unimolecular
C) Trimolecular
D) None of the above
Answer: B) Unimolecular
Explanation: A reaction with a molecularity of 1 involves only one reactant molecule in the rate-determining step, making it unimolecular.
Question 24
What is the unit of the rate constant kk for a second-order reaction?
A) M/s
B) M²/s
C) 1/M·s
D) M/s²
Answer: C) 1/M·s
Explanation: For a second-order reaction, the rate constant
k has units of 1/(M·s), reflecting that the rate depends on the concentration squared.
Question 25
Which of the following factors does NOT affect the rate of a chemical reaction?
A) Temperature
B) Concentration of reactants
C) Presence of a catalyst
D) Color of the reactants
Answer: D) Color of the reactants
Explanation: The color of the reactants does not influence the rate of a chemical reaction. The rate is affected by temperature, concentration, and catalysts.
Question 26
In a reaction where the rate is Rate=k[A]2[B], the overall order of the reaction is:
A) 1
B) 2
C) 3
D) 4
Answer: C) 3
Explanation: The overall order is the sum of the exponents in the rate law: 2+1=3
Question 27
If a reaction has a molecularity of 3, it is most likely:
A) Unimolecular
B) Bimolecular
C) Termolecular
D) Zero order
Answer: C) Termolecular
Explanation: A reaction with a molecularity of 3 involves three reactant molecules and is referred to as termolecular.
Question 28
Which of the following is an example of a zero-order reaction?
A) A→Products
B) A+B→Products
C) 2A→Products
D) None of the above
Answer: A) A→Products
Explanation: A zero-order reaction can proceed without any dependence on the concentration of reactants, making it consistent with the scenario provided.
Question 30
A reaction with a half-life that depends on the initial concentration is most likely:
A) Zero-order
B) First-order
C) Second-order
D) Third-order
Answer: C) Second-order
Explanation: In second-order reactions, the half-life is inversely proportional to the initial concentration, meaning it changes as the concentration changes.
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