Chemical Kinetics Test

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Chemical Kinetics Test - 6

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Question 1
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Direction : Each question has four choices (a), (b), (c) and (d), out of which ONLY ONE is correct.

For a given reaction,

A →Product,

rate = 1 x 10^-4 Ms^-1 at [A] = 0.01 M
rate = 1.41 x 10^-4 Ms^-1 at [A] = 0.02 M

Hence, rate law is

A

B

C

D

Solution

Let rate law be

1 x 10^-4 = K(0.01)ⁿ

1.41 x 10^-4 = K(0.02)ⁿ

∴1.41 = (2)ⁿ

(2)^1/2 = (2)ⁿ (Since, √2 = 1.41)

∴n= 1/2

Thus rate law is
Question 2
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The rate law for a reaction between the substances A and 8 is given by
rate = k[A]ⁿ [B]^m
If concentration of A is doubled and that of B is halved, the new rate as compared to the earlier rate would be

A

B
(m + n)

C
(n - m)

D
2^(n-m)

Solution
Question 3
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The rate equation for the reaction,
2A + B → C
is found to be, rate = k[A] [B]
Q. The correct statement in relation to this reaction is that the

A
unit of k must be s^-1

B
t_1/2 is constant

C
rate of formation of C is half of the rate of disappearance of A

D
value of k is independent of the initial concentration of A and 8

Solution

Rate = k (A)[B]
The given reaction is first order in A and first order is B.
Thus, total order = 2
(a) Unit of k = cone ^{1 - n} time ^-1 = conc^-1 time^-1 Thus, (a) is false.
(b) of second-order reaction, thus (b) is false.
Thus, (c) is correct.

Thus, value of k is dependent on the concentration of A and B. Thus, (d) is false.
Question 4
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For the reaction,
2 A+B →Product
The half-life period was independent of concentration of B. On doubling the concentration A, rate increases two times. Thus, unit of rate constant for this reaction is

A
L mol^-1 s^-1

B
mol L^-1 s^-1

C
unitless

D
S^-1

Solution

t₅₀ is independent of concentration of B then w.r.t. B, (n - 1) = 0. Thus, n = 1
Thus, order w.r.t. B = 1
Also, if concentration is made m-times, rate becomes, mⁿ -times.
Hence, w.r.t.A
m = 2, mⁿ = 2
∴ 2ⁿ = 2 = 2¹
Thus n = 1
Thus, order w.r.t. A = 1
Thus, total order = 2 = n
Unit of n th order reaction = conc^(1-n) time^-1
conc in mol L^-1 and time in seconds.
Then,
Question 5
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Which of the following statements appears to the first order reaction?
2N₂ O₅ (CCl₄ ) → 4NO₂ (CCl₄ ) + O₂ (g)

A
I, II and V

B
I, II and VI

C
II, V and VI

D
I, II and III

Solution

(a)
I, II, V - represent first order equation
III, VI - zeroth order equation
IV - second order equation
Question 6
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For a reaction, time of 75% reaction is thrice of time of 50% reaction. Thus, order of the reaction is

A
0

B
1

C
3

D
2

Solution

For n^th order reaction (n >1)

This equation is true, if n = 2
Question 7
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For nth order reaction,
Graphs between log (rate) and log[A₀ ] are of the type ([A₀ ] is the initial concentration)
Lines P, Q, R and S are for the order

A

B

C

D

Solution

n = order of the reaction =slope of the line
Larger the value of the slope of the line, larger the order.
Thus, P = 3, Q = 2, R = 1, S = 0.
Question 8
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nA → Product
For the reaction, rate constant and rate of the reaction are equal, then on doubling the concentration of A, rate becomes,

A
doubled

B
four times

C
halved

D
constant

Solution

Thus, order = zero Rate is independent of concentration of A.
Thus, rate remains constant.
Question 9
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For the simple reaction,
A →B
When [A] was changed from 0.502 mol dm^-3 to 1.004 mol dm^-3 half-life dropped from 52 s to 26 s at 300 K. Thus, order of the reaction is

A
0

B
1

C
2

D
3

Solution

For nth order reaction,
(T₅₀ ) is t_{1 ,} at [A] = a₁ and is t₂ at [A] = a₂
∴
(2) = (2)^n-1
∴n - 1 = 1, n = 2
Question 10
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For the following reaction,
Variation of T50 with [A] is shown
Q.
After 10 min volume of N₂ (g) is 10 L and after complete reaction, volume of N₂ (g) is 50 L. Thus, T₅₀ is

A
10 min

B
20 min

C
31 min

D
41 min

Solution

T₅₀ is independent of concentration of [A], Thus, it follows first order kinetics.
Question 11
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Kinetics of the following reaction,
can be studied by

A
measurement of pH

B
titration with hypo after adding Kl

C
titration with AgNO₃ solution

D
All of the above

Solution

Cl-atom attached to N-atom, is an oxidising agent and can oxidise Kl to l₂ .

l₂ can be titrated using hypo in iodometric titration.

Cl-atom attached to benzene nucleus is not an oxidising agent.
Question 12
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Graph between [B] and time t of the reaction of the type I for the reaction, A →B
Hence, graph between and time t will be of the type

A

B

C

D

Solution

A →B

[B] increases uniformly with time t. Order is zero. Thus, at every point, = constant