Here below some basic MCQ’s about “Order and Molecularity” with Answer which is explained in details. let’s check one by one which is given below.
Question 1
What is the order of a reaction if its rate is proportional to the concentration of one reactant raised to the power of 2?
A) 1
B) 2
C) 3
D) None of the above
Answer: B) 2
Explanation: The order of a reaction is determined by the sum of the powers of the concentration terms in the rate law. If the rate is proportional to the concentration of one reactant raised to the power of 2, the reaction is second-order with respect to that reactant.
Question 2
Which of the following statements is true regarding molecularity?
A) Molecularity can be a fractional value.
B) Molecularity refers to the number of molecules involved in the rate-determining step.
C) Molecularity is the sum of the orders of all reactants.
D) Molecularity can only be zero or a whole number.
Answer: B) Molecularity refers to the number of molecules involved in the rate-determining step.
Explanation: Molecularity is defined as the number of reactant molecules that collide simultaneously in an elementary reaction. It can only be a whole number (1, 2, 3, etc.) and cannot be fractional.
Question 3
A reaction has a rate law of Rate=k[A]1[B]2. What is the overall order of the reaction?
A) 1
B) 2
C) 3
D) 4
Answer: C) 3
Explanation: The overall order of the reaction is the sum of the exponents in the rate law. Here, it is 1+2=3.
Question 4
If a reaction is said to be zero-order, what does that imply about the concentration of the reactant?
A) The concentration of the reactant remains constant.
B) The reaction rate increases with the concentration of the reactant.
C) The reaction rate is dependent on the concentration of the reactant.
D) The reaction will stop once the concentration is zero.
Answer: A) The concentration of the reactant remains constant.
Explanation: In a zero-order reaction, the rate of reaction is constant and does not depend on the concentration of the reactants. Therefore, even if the concentration decreases, the rate remains the same until the reactants are depleted.
Question 5
Which of the following reactions is most likely to be bimolecular?
A) A → Products
B) A + B → Products
C) 2A → Products
D) A + B + C → Products
Answer: B) A + B → Products
Explanation: Bimolecular reactions involve two reactant molecules in the rate-determining step. The option A + B → Products indicates that two different molecules are involved, making it bimolecular. Option C could also be bimolecular if it involves two molecules of A colliding, but it is less clear than the direct two different reactants in option B.
Question 6
The molecularity of a reaction that involves the simultaneous collision of three reactant molecules is:
A) Unimolecular
B) Bimolecular
C) Trimolecular
D) Zero
Answer: C) Trimolecular
Explanation: Molecularity refers to the number of reactant molecules that participate in an elementary reaction. If three molecules collide simultaneously, the reaction is trimolecular.
Question 7
Which of the following rate laws indicates a first-order reaction?
A) Rate=k[A]0
B) Rate=k[A]1
C) Rate=k[A]2
D) Rate=k[A]3
Answer: B) Rate=k[A]1
Explanation: A first-order reaction has a rate that is directly proportional to the concentration of one reactant raised to the first power. Therefore, Rate=k[A]1 indicates a first-order reaction.
Question 8
In a reaction mechanism, which step is usually the slowest?
A) Fast step
B) Intermediate step
C) Rate-determining step
D) Catalytic step
Answer: C) Rate-determining step
Explanation: The rate-determining step is the slowest step in a reaction mechanism, which determines the overall rate of the reaction.
Question 9
What is the molecularity of a reaction represented by the equation 2A→Products?
A) 1
B) 2
C) 3
D) None of the above
Answer: B) 2
Explanation: In this reaction, two molecules of A are involved in the rate-determining step, making it bimolecular.
Question 10
Which of the following statements about zero-order reactions is true?
A) The reaction rate decreases as the reactant concentration decreases.
B) The reaction can proceed without any reactant.
C) The concentration of the reactant affects the rate.
D) The rate is constant regardless of the concentration of reactants.
Answer: D) The rate is constant regardless of the concentration of reactants.
Explanation: In a zero-order reaction, the rate is independent of the concentration of the reactants, remaining constant until the reactants are exhausted.
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