Question 31
If the rate of a reaction doubles when the concentration of reactant A is doubled, the reaction is:
A) Zero-order
B) First-order
C) Second-order
D) Third-order
Answer: B) First-order
Explanation: A reaction is first-order if doubling the concentration of one reactant results in a doubling of the rate.
Question 32
In an elementary reaction, which of the following describes the relationship between molecularity and order?
A) Molecularity and order are always equal.
B) Molecularity can be fractional, but order cannot.
C) Molecularity is always greater than order.
D) They are not necessarily related.
Answer: D) They are not necessarily related.
Explanation: Molecularity refers to the number of molecules in an elementary step, while order is based on the rate law and can be influenced by various factors.
Question 33
If a catalyst is added to a reaction, what is the likely effect on the activation energy?
A) It increases.
B) It decreases.
C) It remains the same.
D) It becomes undefined.
Answer: B) It decreases.
Explanation: Catalysts provide an alternative reaction pathway with a lower activation energy, thereby increasing the rate of the reaction.
Question 34
Which of the following is a characteristic of a first-order reaction?
A) Rate is constant
B) Half-life is dependent on initial concentration
C) Rate doubles with concentration doubling
D) Molecularity can be zero
Answer: C) Rate doubles with concentration doubling
Explanation: In first-order reactions, the rate is directly proportional to the concentration of the reactant, so doubling the concentration doubles the rate.
Question 35
In a reaction that is third order overall, which of the following could be a possible rate law?
A) Rate=k[A]3
B) Rate=k[A][B]
C) Rate=k[A]2[B]
D) All of the above
Answer: D) All of the above
Explanation: All the given options can sum to an overall order of 3 depending on the combinations of reactants involved.
Question 36
Which of the following reactions would likely be unimolecular?
A) A+B→C
B) 2A→Products
C) A→Products
D) A+2B→C
Answer: C) A→Products
Explanation: A unimolecular reaction involves only one reactant molecule in the rate-determining step.
Question 37
For a reaction to be classified as bimolecular, it must involve:
A) One molecule
B) Two molecules colliding
C) Three molecules
D) Any number of molecules
Answer: B) Two molecules colliding
Explanation: Bimolecular reactions involve the simultaneous collision of two reactant molecules in the rate-determining step.
Question 38
Which of the following scenarios could represent a second-order reaction?
A) 2A→Products
B) A+B→Products
C) A+A→Products
D) Both A and C
Answer: D) Both A and C
Explanation: Both 2A→Products and A+A→Products are examples of reactions that could be second-order, involving two molecules of A.
Question 39
If a reaction’s rate is described by Rate=k[A]3[B]0, what can be concluded about reactant B?
A) It is involved in the reaction.
B) It has no effect on the reaction rate.
C) It is a catalyst.
D) It is in excess.
Answer: B) It has no effect on the reaction rate.
Explanation: The exponent of B is 0, meaning that changes in the concentration of B do not affect the rate of the reaction.
Question 40
The reaction A+2B→Products has a rate law of Rate=k[A]1[B]2. What is the overall order?
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: 1+2=3.
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