Chemistry XII+ - Chemical Kinetics 04

Question : 1

(skipped)

Rate constant for the hydrolysis of ester in acidic medium is calculated by the formula

Options:

Solution :

(4)

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Question : 2

(skipped)

Which is incorrect regarding pseudo first order reaction?

Options:

	It follows first order kinetics
	One of the reactants is present in large excess
	Its molecularity is also one
	Inversion of cane sugar is pseudo first order reaction

Solution :

(3)

Molecularity of pseudo 1st order reaction
is not one.

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Question : 3

(skipped)

For the reaction, 2H₂O₂  2H₂O + O₂ . The mechanism given is

H₂O₂ + I⁽⁻⁾ H₂O + IO⁻

H₂O₂ + IO⁻  H₂O +I⁻ + O₂

The rate equation for the above reaction is given as

Options:

	Rate = k [H2O2]2
	Rate = k [H2O2]2[I−]1
	Rate = k [H2O2] [I−]
	Rate = k [I−]

Solution :

(3)

Slow step is rate determining step .
∴ Rate = k [H₂O₂][I^–]

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Question : 4

(skipped)

If for the reaction 2N₂O₅ →4NO₂ + O₂, experimentally found that it is first order w.r.t. N₂O₅ then the mechanism which is followed correctly

Options:

	N2O5 NO2 +NO3 N2O5 +NO3 3NO2 + O2
	N2O5 NO2 +NO3 N2O5 +NO3 3NO2 + O2
	One step reaction 2N2O5 →4NO2 + O2
	Both (1) & (2)

Solution :

(2)

As order w.r.t N₂O₅ is one

Hence, for slow
N₂O₅ NO₂ +NO₃
Rate ∝ [N₂O₅]

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Question : 5

(skipped)

Consider a reaction,
 A → B +  C + D
(g)   (g)   (g)   (g)

If at the end of 20 min, pressure of the system is 170 torr and on complete dissociation of (A) it becomes 270 torr. Then the initial pressure of the system and pressure of B after 20 min is respectively

Options:

	170, 90 torr
	170, 50 torr
	90, 40 torr
	90, 50 torr

Solution :

(3)

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Question : 6

(skipped)

For the reaction
 2X→ 2Y +  Z
 (g)     (g)   (g)
If initial pressure of x is P_i and after time t the total pressure becomes P_t, then the correct expression for rate constant is

Options:

Solution :

(2)

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Question : 7

(skipped)

For the reaction, 2O₃ →3O₂
Mechanism given is

(a)O₃ O₂ +O (fast)

( b)O₃ + O  2O₂

Then overall order of above reaction is

Options:

	–1
	1
	2
	3

Solution :

(2)

Rate = k [O₃][O]
As [O] is intermediate

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Question : 8

(skipped)

For inversion of sucrose, the correct rate expression is

Options:

	Rate = k [C12H22O11] [H2O]
	Rate = k [C12H22O11]
	Rate = k [H2O]
	Rate = k [C12H22O11]2

Solution :

(2)

H₂O is present in excess, Hence, Rate =
k [C₁₂H₂₂O₁₁]

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Question : 9

(skipped)

For a complex reaction, which is true?

Options:

	Slow step is rate determining step
	Molecularity has no meaning
	Molecularity of slow step is same as order of overall reaction
	All of these

Solution :

(4)

All statements are correct

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Question : 10

(skipped)

If for hydrolysis of ester, Rate = k′ [ester] [H₂O], [H₂O] is taken constant, the equation becomes Rate = k [ester]. Therefore k is

Options:

	k = k′ [H2O]
	k′ = k[H2O]
	k = k′ [ester]
	Both (1) & (3)

Solution :

(1)

Fact.