250+ TOP MCQs on Reaction Order and Elementary Rate Law and Answers

Chemical Reaction Engineering Multiple Choice Questions & Answers on “Reaction Order and Elementary Rate Law”.

1. Molecularity refers to an elementary reaction.
A. True
B. False
Answer: A
Explanation: Elementary reaction occurs in single reaction step with no intermediates and molecularity is the number of particles involved in the reaction.

2. Molecularity is ___________ value and order is ___________ value.
A. an integer, a fractional
B. a fractional, an integer
C. both fractional
D. both integers
Answer: A
Explanation: Order is empirical, hence can be a fractional value but molecularity refers to the mechanism and is applicable only for elementary reactions.

3. The overall order of reaction for –r_A = kC_A^0.7C_B^1.3 is _______
A. 0
B. 1
C. 2
D. 3
Answer: C
Explanation: Order w.r.t A is 0.7 and B is 1.3.Hence, Overall order is 2.

4. What is the relative rate of reaction for the given reaction.
2A + 9B → 7C + 4D
A. –r_A = -9rB=7rC=–4rD
B. –r_A =-rB/9=rC/7=rD/4
C. –r_A =-rB/9=7rC=4rD
D. –r_A = 9rB=-7rC=–4rD
Answer: B
Explanation: Relative rate of reaction can be obtained from the ratio of stoichiometric co -efficient.

5. The units of rate constant of n^th order is ___________
A. time^-1
B. concentration^(n-1)
C. time^-1 concentration^(1-n)
D. time^-1 concentration^(n-1)
Answer: C
Explanation: General expression for the rate constant is time^-1 concentration^(1-n).

6. The unit for concentration equilibrium constant for the following reaction is _________
2A + 9B ←→7C + 4D
A. ((frac{mol}{dm^3}))²
B. ((frac{mol}{dm^3}))⁹
C. ((frac{mol}{dm^3}))^-4
D. ((frac{mol}{dm^3}))^-3
Answer: D
Explanation: Concentration eqm constant for a reversible reaction is
aA + bB → cC + dD is
K = (frac{cC^c cD^d}{cA^a cB^b}) unit is ((frac{mol}{dm^3}))^c+d-a-b when it is applied to the above equation we get -3.

7. The overall reaction order for A + B → C + D is two. It implies that ______
A. reaction may be non-elementary and molecularity is two
B. reaction may be elementary and molecularity is two
C. reaction is non-elementary and molecularity is two
D. reaction is elementary and molecularity is two
Answer: D
Explanation: Order is equal to molecularity when reaction is elementary.

8. Reaction corresponding to stoichiometric equation is called __________
A. Non-elementary
B. Elementary
C. Heterogeneous
D. Homogeneous
Answer: B
Explanation: Elementary reactions are the ones with single reaction step and the reaction rate corresponds to stoichiometric equation.

9. The rate constant for a first order reaction depends on _____________
A. Pressure
B. Temperature
C. Concentration
D. Time
Answer: B
Explanation: The reaction rate constant depends on temperature only.

10. The mlecularity of the following single step reaction is ___________
aA + bB → pP
A. a+b-p
B. a+b+p
C. a+b
D. a-p
Answer: C
Explanation: The above single step reaction is an elementary reaction. Molecularity is the number of molecules participating in the reaction.

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