Question 81
In the reaction mechanism, if an intermediate is formed, it will:
A) Appear in the final products
B) Not appear in the final reaction equation
C) Be consumed in the same step it is produced
D) Be a catalyst
Answer: B) Not appear in the final reaction equation
Explanation: Intermediates are produced and consumed in the reaction mechanism but do not appear in the overall balanced equation.
Question 82
The rate constant kk for a reaction is affected by:
A) Temperature only
B) Concentration only
C) Pressure only
D) Temperature and concentration
Answer: A) Temperature only
Explanation: The rate constant kk is dependent on temperature; changes in temperature can significantly alter kk.
Question 83
In a first-order reaction, if the rate constant kk is 0.1 s−1−1, what will be the half-life?
A) 6.93 s
B) 10 s
C) 20 s
D) 0.693 s
Answer: A) 6.93 s
Question 84
If a reaction’s rate is given as Rate=k[A]1[B]1[C]1, the overall reaction order is:
A) 1
B) 2
C) 3
D) 4
Answer: C) 3
Explanation: The overall order is the sum of the exponents: 1+1+1=3
Question 85
Which of the following is a characteristic feature of second-order reactions?
A) The rate is independent of concentration.
B) The half-life is dependent on the initial concentration.
C) The rate increases linearly with time.
D) The concentration of the reactants decreases exponentially.
Answer: B) The half-life is dependent on the initial concentration.
Explanation: For second-order reactions, the half-life increases as the initial concentration decreases.
Question 86
What will happen to the rate of a reaction if the temperature is increased?
A) It will always decrease.
B) It will remain the same.
C) It will increase due to more energetic collisions.
D) It will fluctuate unpredictably.
Answer: C) It will increase due to more energetic collisions.
Explanation: Increasing temperature generally increases molecular energy, leading to more frequent and effective collisions.
Question 87
In a reaction that is third-order overall, which of the following is NOT a valid rate law?
A) Rate=k[A]3
B) Rate=k[A]2[B]1
C) Rate=k[A]1[B]2[C]0
D) Rate=k[A]1[B]1[C]1
Answer: D) Rate=k[A]1[B]1[C]1
Explanation: The option D adds up to an order of 3, but it requires three different reactants which can be misleading in a third-order context.
Question 88
Which of the following would NOT typically be classified as a reaction intermediate?
A) A product formed in an early step
B) A reactant that appears in the rate-determining step
C) A species that is formed and consumed in subsequent steps
D) A catalyst
Answer: D) A catalyst
Explanation: A catalyst is not consumed in the reaction and facilitates the process but does not appear as an intermediate.
Question 89
For a reaction that is second-order with respect to reactant A, what is the relationship between concentration and rate?
A) Linear
B) Exponential
C) Quadratic
D) Logarithmic
Answer: C) Quadratic
Explanation: In second-order reactions, the rate is proportional to the square of the concentration of A, leading to a quadratic relationship.
Question 90
In the reaction A+B→CA+B→C, if the rate law is Rate=k[A]1[B]2Rate=k[A]1[B]2, which reactant is in excess?
A) A
B) B
C) C
D) None of the above
Answer: B) B
Explanation: Since B has a higher order in the rate law, it suggests that it is likely present in excess to maintain the rate.
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