Question 61
If the reaction rate is found to be constant over time, the reaction is most likely:
A) First-order
B) Second-order
C) Zero-order
D) Pseudo-first-order
Answer: C) Zero-order
Explanation: In a zero-order reaction, the rate remains constant regardless of the concentration of the reactants until they are depleted.
Question 62
The half-life of a zero-order reaction is:
A) Independent of initial concentration
B) Directly proportional to initial concentration
C) Inversely proportional to initial concentration
D) Constant
Answer: B) Directly proportional to initial concentration
Explanation: In a zero-order reaction, the half-life increases as the initial concentration increases.
Question 63
For the reaction 2A+B→C, if the rate law is Rate=k[A]2[B], what is the order of the reaction with respect to B?
A) 1
B) 2
C) 3
D) 4
Answer: A) 1
Explanation: The order with respect to B is given by the exponent in the rate law, which is 1.
Question 64
Which of the following factors will NOT affect the activation energy of a reaction?
A) Nature of the reactants
B) Temperature
C) Presence of a catalyst
D) Reaction pathway
Answer: B) Temperature
Explanation: While temperature affects the rate of reaction, it does not change the inherent activation energy of the reaction itself.
Question 66
For a reaction with an overall order of 3, which of the following rate laws is possible?
A) Rate=k[A]1[B]2
B) Rate=k[A]3
C) Rate=k[A]2[B]1
D) All of the above
Answer: D) All of the above
Explanation: All the given options represent valid rate laws that can sum to an overall order of 3.
Question 67
The molecularity of a reaction is always a whole number. This is because:
A) It represents the stoichiometry of the overall reaction.
B) It describes the concentration of reactants.
C) It reflects the number of molecules involved in an elementary step.
D) It is derived from the rate constant.
Answer: C) It reflects the number of molecules involved in an elementary step.
Explanation: Molecularity refers to the number of reactant molecules in the elementary step, which must be a whole number.
Question 68
If a reaction is second order in respect to A and zero order in respect to B, which of the following rate laws is correct?
A) Rate=k[A]2[B]1
B) Rate=k[A]2[B]0
C) Rate=k[A]1[B]2
D) Rate=k[A]0[B]0
Answer: B) Rate=k[A]2[B]0
Explanation: The rate law must reflect the orders correctly; since B is zero-order, it contributes nothing to the rate.
Question 69
In a second-order reaction, if the half-life of the reaction is known, it can be expressed as:
A) 0.693kk0.693
B) 1k[A]0k[A]01
C) 2kk2
D) 12k2k1
Answer: B) 1k[A]0k[A]01
Explanation: The half-life of a second-order reaction is inversely proportional to the initial concentration of the reactant.
Question 70
Which of the following is true regarding molecularity?
A) It can be a fraction.
B) It can be zero.
C) It is determined from the rate law.
D) It refers only to the slowest step in a mechanism.
Answer: D) It refers only to the slowest step in a mechanism.
Explanation: Molecularity is specifically defined for elementary reactions, reflecting the number of molecules involved in the rate-determining step.
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