Question 51
In a reaction mechanism, the step with the highest activation energy is known as:
A) The fast step
B) The rate-determining step
C) The intermediate step
D) The catalytic step
Answer: B) The rate-determining step
Explanation: The rate-determining step is the slowest step with the highest activation energy, which limits the overall reaction rate.
Question 52
If the rate of a reaction is found to be dependent on the concentration of two different reactants, it indicates that the reaction is:
A) Unimolecular
B) Bimolecular
C) Trimolecular
D) Zero-order
Answer: B) Bimolecular
Explanation: A bimolecular reaction involves two reactant molecules in the rate-determining step, reflecting that the rate is dependent on the concentrations of both.
Question 53
The activation energy for a reaction can be lowered by:
A) Increasing the temperature
B) Increasing the concentration
C) Adding a catalyst
D) Decreasing the volume
Answer: C) Adding a catalyst
Explanation: Catalysts lower the activation energy barrier for a reaction, increasing the reaction rate without being consumed in the process.
Question 54
For a zero-order reaction, what is the relationship between concentration and time?
A) Linear
B) Exponential
C) Inversely proportional
D) Quadratic
Answer: A) Linear
Explanation: In a zero-order reaction, the concentration decreases linearly over time, as the rate is constant regardless of the concentration.
Question 55
If the rate law of a reaction is Rate=k[A]1[B]1, what is the overall order of the reaction?
A) 1
B) 2
C) 3
D) 4
Answer: B) 2
Explanation: The overall order is the sum of the exponents: 1+1=2.
Question 56
What effect does a catalyst have on the equilibrium constant of a reaction?
A) Increases it
B) Decreases it
C) Does not affect it
D) Changes it based on concentration
Answer: C) Does not affect it
Explanation: Catalysts speed up the rate at which equilibrium is reached but do not change the position of equilibrium or the equilibrium constant.
Question 57
In a reaction where the rate is given by Rate=k[A]2, if the concentration of A is halved, the rate will:
A) Stay the same
B) Halve
C) Quarter
D) Double
Answer: C) Quarter
Explanation: If the concentration of A is halved, the rate will decrease by a factor of (1/2)2=1/4
Question 58
A reaction mechanism that has two elementary steps, where the first step is fast and the second step is slow, is known as:
A) An overall mechanism
B) A complex mechanism
C) A simple mechanism
D) A chain mechanism
Answer: B) A complex mechanism
Explanation: A mechanism with multiple steps, particularly where one is slow, is considered complex because it involves interactions between multiple species.
Question 59
Which of the following would be classified as a unimolecular reaction?
A) A+B→C
B) A→Products
C) 2A+B→C
Answer: B) A→Products
Explanation: A unimolecular reaction involves only one reactant molecule in the rate-determining step.
Question 60
In a first-order reaction, the half-life is defined as the time required for the concentration of the reactant to:
A) Decrease to zero
B) Double
C) Decrease to half its initial value
D) Increase to double its value
Answer: C) Decrease to half its initial value
Explanation: The half-life of a first-order reaction is the time it takes for the concentration of the reactant to reduce to half of its initial concentration.
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