Test: Collision Theory & Reaction Mechanism
22 Questions MCQ Test Topic-wise MCQ Tests for NEET | Test: Collision Theory & Reaction Mechanism
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Direction (Q. Nos. 1-14) This section contains 14 multiple choice questions. Each question has four choices (a), (b), (c) and (d), out of which ONLY ONE is correct.
A chemical reaction proceeds through the following steps :
Step I, 2A ⇌ X fast
Step II, X+B ⇌ Y slow
Step III, Y+B ⇌ Product fast
Q. The rate law for the overall reaction is
Step II, X+B ⇌ Y slow
Step III, Y+B ⇌ Product fast
By slow step II,
By reversible fast step
∴ 
∴
The following reaction obey rate law
It can follow mechanism
I. NO2 + O3 
NO3 + O2 ,
NO3+NO2 
N2O5
II. NO2 + O 
NO3
NO3+NO2 
N2O5
Select the correct mechanism.
NO3 + O2 , N2O5 NO3 N2O5 In I, slow step is
Thus,
∴ 
In fast reversible step,
∴
∴
A chemical reaction is said to take place through the various stages with ΔG° values indicated by the graph:
Stages I and II represent respectively
I is reaction intermediate while II is transition complex.
Following reaction takes place by mechanism:
Step I
Step II
Hence 
for the given reaction is
Slow step I is the rate-determining step.
By slow step II,
By fast step l,
∴
Net reaction is
Thus, rate law is based on the slow step.
For the reaction,
A + 2B → C+ D
The rate law is k [A] [B] .
Select the correct statement.
(a) Slow step is the rate-determining step, thus by
rate law = k[A][B]
Net reaction,
Thus, this mechanism is not consistent with the stoichiometry, but is consistent with rate law.
(b) By slow step,
Rate law = k3[A][B2]
By fast step,
∴ 
∴ 
Thus, this mechanism is consistent with the stoichiometry of the net reaction but not with the rate law.
Thus, (b) is correct.
For the reaction, 
Mechanism is given by
Rate law is true, if
If step II is fast and reversible, then
∴ 
∴ 
For the following SN reaction, 
Rate-determining step is
H2O is a weak nucleophile and cannot attack tertiary carbon of maximum electron density directly. Thus, rate-determining slow step is
step is
and rate law is 
and [H2O] is not involved.
It is SN1 reaction.
Reaction between nitric oxide and hydrogen takes place by the following mechanism:
Q.
Rate of the overall reaction in terms of the concentration of the reactants is
Slow step II is the rate-determining step.
...(1)
By step I in equilibrium,
∴ 
Put the value of [N2O2] in Eq. (i), we get
∴ 
Consider the following reaction,
The rate equation for this reaction is, rate = k[CI2] [H2S]
Which of these mechanisms is/are consistent with this rate equation?
[AIEEE2010]
Slow step is the rate-determining step.
and
∴ 
which is not the rate law.
The following mechanism has been proposed for the reaction,
It involves the following steps:
Q.
The order of the reaction w.r.t. NO(g) is
From slow step,
From equilibrium step,
∴ 
Consider the three following proposed mechanism for the overall equation.
Q.
Which mechanism predicts a third order reaction?
It is second order in A and first order in B thus, total order = 3.
II. 
∴ 
Thus, it is second order in A and first order in B.
Total order = 3
Thus, it is second order in A and first order in B.
Thus total order = 3
Consider the following proposed mechanism :
Based on the following steps:
Rate law is
Slow step (II) is the rate-determining step.
By fast step I in equilibrium.
∴ 
∴ 
Direction (Q. Nos. 15- 20) This section contains 3 paragraphs, each describing theory, experiments, data, etc., Six questions related to the paragraphs have been given. Each question has ONLY ONE correct answer among the four given options (a), (b), (c) and (d).
Passage I
The ozone in the earth’s ozone layer decomposes according to the equation,
It involves
(Time is in seconds and concentration in mol L-1)
Q.
Rate of disappearance of O3 is
Step / is fast and reversible
Step // is slow and rate-determining step.
∴ 
∴ 
∴ 
where, k1 keq
Passage I
The ozone in the earth’s ozone layer decomposes according to the equation,
It involves
(Time is in seconds and concentration in mol L-1)
Q.
What is the rate at a time of 50% decomposition of O3, when [O3]0 = 1.0 M?
Step / is fast and reversible
Step // is slow and rate-determining step.
∴ 
∴ 
∴
where, 
Passage II
N2O5 decomposes according to the following equation:
The following mechanism has been given:
Q.
Rate of formation of O2 is given by
Half-life period is independent of [N2O5]. Hence, it is first order reaction.
Passage II
N2O5 decomposes according to the following equation:
The following mechanism has been given:
Q.
Half-life period is independent of the concentration of N2O5. Thus,
Half-life period is independent of [N2O5]. Hence, it is first order reaction.
Passage III
is believed to proceed through the following three step mechanism:
Q.
Identify the false statement.
Molecularity of each step is two thus, true.
Thus, (a) is correct.
The limiting step of a complex reaction is always the slowest, thus (b) is correct.
It involves more than one elementary step, thus, it is a complex reaction. Thus, (d) is also correct.
HOCl appears in step I and disappears in step II, Thus it is an intermediate.
HOI appears in step II and disappears in step III. Thus, HOI is also an intermediate.
Thus, (c) is incorrect.
Slow step il is the rate-determining step.
Note H2O as reactant is not taken in equilibrium and rate expression.
Passage III
is believed to proceed through the following three step mechanism:
Q.
What is the rate equation of the reaction?
Molecularity of each step is two thus, true.
Thus, (a) is correct.
The limiting step of a complex reaction is always the slowest, thus (b) is correct.
It involves more than one elementary step, thus, it is a complex reaction. Thus, (d) is also correct.
HOCi appears in step I and disappears in step II, Thus it is an intermediate.
HOI appears in step II and disappears in step III. Thus, HOI is also an intermediate.
Thus, (c) is incorrect.
Slow step il is the rate-determining step.
Note H2O as reactant is not taken in equilibrium and rate expression.
Direction (Q. Nos. 21 and 22) This section contains 2 questions. When worked out will result in one integer from 0 to 9 (both inclusive).
Consider the following proposed mechanism:
(rate constant =k ) to describe the overall equations
Q.
What is the order predicted by the proposed mechanism?
Rate determining step is 
The reaction is third order in A and first order in B.
Total order = 3 + 1 = 4
For the overall reaction between A and 6 to yield C and D, two mechanisms are proposed.
Q.
At what concentration of A and/or B will the inherent rates be equal?
Thus, 
is fast and rate-determining step is
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