Question Set B

cbse 12th Standard Chemistry Chemical Kinetics Important Questions And Answers Study Material - QB365

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Questions:

Multiple Choice Question

20 x 1 = 20

Compounds A and C in the following reaction are

(a)

identical

(b)

positional isomers

(c)

functional isomers

(d)

optical isomers

Of the following which is the product formed when cyclohexanone undergoes aldol condensation followed by heating?

(a)

(b)

(c)

(d)

In Arrhenius plot of Ink Vs \(\frac{1}{\mathrm{~T}}\) is a linear plot obtained with slope of -2 x 10⁴ k. Ea of reaction in kJ mol ^-1.

(a)

(b)

166

(c)

249

(d)

332 kJ mol ^-1

For a reaction taking place in three steps, the overall rate constant k \(=\frac{k_{1} k_{2}}{k_{3}}\) If Ea₁, Ea₂ and Ea₃ are the 40, 50 and 60 kJ mol^-1, the overall E_a is

(a)

(b)

(c)

(d)

Arrhenius equation may not be represented as

(a)

\( \ln \frac{A}{k}=\frac{E_{a}}{R T}\)

(b)

\(K=Ae^-Ea/RT\)

(c)

\(\log A=\log k+\frac{E_{\alpha}}{2303 R T}\)

(d)

\(\log k-\left(\frac{E_{a}}{R T}\right)=A\)

In Clemmensen reduction, carbonyl compound is treated with _____________ .

(a)

Zinc amalgam + HCI

(b)

Sodium amalgam + HCI

(c)

Zinc amalgam + nitric acid

(d)

Sodium amalgam + HNO₃

Which of the following compounds will give butanone on oxidation with alkaline KMnO₄ solution?

(a)

Butan - I - oI

(b)

Butan - 2 - ol

(c)

Both of these

(d)

None of these

Which of the following acids on heating loses a molecule of H2O to form an \(\alpha , \beta\) - unsaturated acid ?

(a)

CH₃CHOCOOH

(b)

HOCH₂COOH

(c)

CH₃CHOHCH₂COOH

(d)

HOCH₂CH₂CH₂COOH

The correct order of decreasing acid strength of trichloroacetic (A), trifluoroacetic acid (B), benzoic acid (C) and formic acid (D) is

(a)

A > B > C > D

(b)

A > C > B > D

(c)

B > A > D > C

(d)

B > A > C > D

10.

Trichloroacetaldehyde was subjected to Cannizaro's reaction by using NaOH. The mixture and another products contains sodium trichloroacetate and other compound. The other compound is

(a)

trichloromethanol

(b)

2,2,2-trichloropropanol

(c)

chloroform

(d)

2,2,2-trichloromethanol

11.

Iodofrom test is not given by

(a)

2-pentanone

(b)

3-pentanone

(c)

ethanal

(d)

ethanol

12.

Which one of the following is reduced with zinc and hydrochloric acid to give the corresponding hydrocarbon ?

(a)

ethyl acetate

(b)

acetic acid

(c)

acetamide

(d)

butan-2-one

13.

Methyl ketones are characterized through

(a)

Tollens' reagent

(b)

Iodoform test

(c)

Schiff's reagent

(d)

Fehling's solution

14.

The chemical that undergoes self-oxidation and self-reduction in the same reaction is

(a)

benzyl alcohol

(b)

acetone

(c)

formaldehyde

(d)

acetic acid

15.

Which of the following organic compounds answers both iodoform test and Fehling's test?

(a)

Ethanal

(b)

Propanone

(c)

Ethanol

(d)

Methanol

16.

For an endothermic reaction, where \(\triangle H\) represents the enthalpy of the reaction in kJ/mol. The minimum value for the energy of activation will be

(a)

less than \(\triangle H\)

(b)

zero

(c)

more than \(\triangle H\)

(d)

equal to \(\triangle H\)

17.

For a first order reaction, the time taken to reduce the initial concentration by a factor of \(\frac {1}{4}\) is 20 minutes. The time required to reduce initial concentration by a factor of 1/16 is

(a)

20 min

(b)

10 min

(c)

80 min

(d)

40 min

(e)

5 min

18.

Which of the following statements is not correct about order of a reaction ?

(a)

The order of a reaction can be a fractional number

(b)

Order of a reaction is experimentally determined quantity.

(c)

The order of a reaction is always equal to the sum of the stoichiometric coeffecients of reactants in the balanced chemnical equation for reaction.

(d)

The order of a reaction is the sum of the powers of molar concentration of the reaction in the rate law expression.

19.

Rate constant of a reaction (k) is 175 litre² mol^-2 sec^-1. What is the order of reaction?

(a)

first

(b)

second

(c)

third

(d)

zero

20.

Time required for 100 percent completion of a zero order reaction is

(a)

\(\frac {2k}{a}\)

(b)

\(\frac {a}{2k}\)

(c)

\(\frac {a}{k}\)

(d)

a k

Assertion and reason

20 x 1 = 20

21.

Assertion: According to steady state hypothesis, in a multistep reaction, the change in concentration with time for reactive intermediates is zero.
Reason: The intermediates are so reactive that after a brief initial period their concentrations rise from zero to a small value and remains constant for most of the duration of the reaction.
Codes:
A) If both assertion and reason are true and the reason is the correct explanation of the assertion.
B) If both assertion and reason are true but reason is not the correct explanation of the assertion.
C) If assertion is true but reason is false.
D) If the assertion and reason both are false.
E) If assertion is false but reason is true.

22.

Assertion: If the activation energy of a reaction is zero, temperature will have no effect on the rate constant.
Reason: Lower the activation energy, faster is the reaction.
Codes:
A) If both assertion and reason are true and the reason is the correct explanation of the assertion.
B) If both assertion and reason are true but reason is not the correct explanation of the assertion.
C) If assertion is true but reason is false.
D) If the assertion and reason both are false.
E) If assertion is false but reason is true.

23.

Assertion: Benzoic acid does not undergo Freidel Crafts reaction.
Reason: The carboxyl group in benzoic acid donates electrons into the ring through resonance
Codes:
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but the reason is not the correct explanation of the assertion.
(c) If the assertion is true but the reason is false.
(d) If the assertion is false but the reason is true.
(e) If the assertion and reason both are false

24.

Assertion: Isobutanal does not give an iodoform test.
Reason: It does not have ∝-hydrogen.
Codes:
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but the reason is not the correct explanation of the assertion.
(c) If the assertion is true but the reason is false.
(d) If the assertion is false but the reason is true.
(e) If the assertion and reason both are false

25.

Assertion : Compounds containing –CHO group are easily oxidised to corresponding carboxylic acids.
Reason : Carboxylic acids can be reduced to alcohols by treatment with LiAlH₄
Codes:
(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
(b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
(c) If the Assertion is correct but Reason is incorrect.
(d) If both the Assertion and Reason are incorrect.

26.

Assertion (A) Fomaldehyde is a planar molecule.
Reason (R) It contains sp²-hybridised carbon atom.
(a) Both (A) and (R) are correct and (R) is the correct explanation of (A).
(b) Both (A) and (R) are correct but (R) is not the correct explanation of(A).
(c) (A) is correct but (R) is incorrect.
(d) (A) is incorrect but (R) is correct.

27.

Assertion: The \(\alpha\)-hydrogen atom in carbonyl compounds is less acidic.
Reason: The anion formed after the loss of \(\alpha\)-hydrogen atom is resonance stabilised.
Codes:
(a) Assertion and reason both are correct and reason is correct explanation of assertion.
(b) Assertion and reason both are wrong statements.
(c) Assertion is correct but reason is wrong statement.
(d) Assertion is wrong but reason is correct statement.
(e) Assertion and reason both are correct statements but reason is not correct explanation of assertion.

28.

Assertion: Aromatic aldehydes and formaldehyde undergo Cannizzaro reaction.
Reason: Aromatic aldehydes are almost as reactive as formaldehyde.
Codes:
(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.

29.

Assertion: Nitration of benzoic acid gives m-nitrobenzoic acid.
Reason: Carboxyl group increases the electron density at the meta-position.
Codes:
(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.

30.

Assertion: Acetic acid in vapour state shows a molecular mass of 120.
Reason: It undergoes intermolecular hydrogen bonding.
Codes:
(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.

31.

Assertion: Benzaldehyde undergoes aldol condensation.
Reason: Aldehydes having a- hydrogen atom undergo aldol condensation.
Codes:
(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.

32.

Assertion: Aldol condensation can be catalysed both by acids and bases.
Reason: \(\beta\)-Hydroxy aldehydes or ketones readily undergo acid catalysed dehydration.
Codes:
(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.

33.

Assertion : Kinetics explains the reaction mechanism.
Reason : Kinetics explains the formation of products.
Codes :
(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.

34.

Assertion : Chemical kinetics deals with the rate of reaction, the factors affecting the rates of the reactions and the mechanism by which the reaction proceed.
Reason : Nature of reactants, concentration of reactants, products and catalyst affect the rate of reaction.
Codes :
(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.

35.

Assertion : Hydrolysis of cane sugar is a pseudo first order reaction.
Reason : Water is present in large excess during hydrolysis.
Codes :
(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.

36.

Assertion : For the reaction, \(2 \mathrm{~N}_{2} \mathrm{O}_{5} \rightarrow 4 \mathrm{NO}_{2}+\mathrm{O}_{2}\)
Rate = k [N₂O₅]
Reason : Rate of decomposition of \(\mathrm{N}_{2} \mathrm{O}_{5}\) is determined by slow step.
Codes :
(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.

37.

Assertion : The decomposition of NH3 on finely divided platinum surface is first order when the concentration is low, however at higher concentration, the reaction becomes zero order.
Reason : In first order reaction, the rate of reaction is proportional to the first power of the concentration of the reactant
Codes :
(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.

38.

In the following questions. an Assertion (A) is followed by a corresponding Reason (R) Use the following keys to choose the appropriate answer.
Assertion (A) Carboxylic acids have higher boiling liquids than aldehydes, ketones and even alcohols of comparable molecular masses.
Reason (R) More extensive association of carboxylic acid molecules through intermolecular hydrogen bonding is responsible for the high boiling point of carboxylic acid.
Codes:
(a) Both (A) and (R) are correct, (R) is the correct explanation of (A).
(b) Both (A) and (R) are correct, (R) is not the correct explanation of (A). .
(c) (A) is correct; (R) is incorrect.
(d) (A) is incorrect; (R) is correct.

39.

In the following questions. an Assertion (A) is followed by a corresponding Reason (R) Use the following keys to choose the appropriate answer.
Assertion (A) \(\alpha\)-hydrogen atoms of carbonyl compounds are acidic.
Reason (R) The strong electron releasing effect of the carbonyl group make the stabilisation of the conjugate base by the resonance.
Codes:
(a) Both (A) and (R) are correct, (R) is the correct explanation of (A).
(b) Both (A) and (R) are correct, (R) is not the correct explanation of (A). .
(c) (A) is correct; (R) is incorrect.
(d) (A) is incorrect; (R) is correct.

40.

In the following questions. an Assertion (A) is followed by a corresponding Reason (R) Use the following keys to choose the appropriate answer.
Assertion (A) A positive catalyst increases the rate of reaction.
Reason (R) A catalyst increases the rate of reaction by making available a new and more efficient mechanism.
Codes:
(a) Both (A) and (R) are correct, (R) is the correct explanation of (A).
(b) Both (A) and (R) are correct, (R) is not the correct explanation of (A).
(c) (A) is correct; (R) is incorrect.
(d) (A) is incorrect; (R) is correct.

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Answers Key:

Multiple Choice Question

20 x 1 = 20

(b)
positional isomers

(b)
166

(a)
30

(d)
\(\log k-\left(\frac{E_{a}}{R T}\right)=A\)

(a)
Zinc amalgam + HCI

(b)
Butan - 2 - ol

10.

(d)
2,2,2-trichloromethanol

11.

(b)
3-pentanone

12.

(d)
butan-2-one

13.

Methyl ketones are characterized by iodoform test

14.

15.

(a)
Ethanal

16.

(a)
less than \(\triangle H\)

17.

(d)
40 min

18.

(c)
The order of a reaction is always equal to the sum of the stoichiometric coeffecients of reactants in the balanced chemnical equation for reaction.

19.

20.

Assertion and reason

20 x 1 = 20

21.

A) If both assertion and reason are true and the reason is the correct explanation of the assertion.

22.

B) If both assertion and reason are true but reason is not the correct explanation of the assertion.
Explanation:
According to Arrhenius equation, K=Ae−Ea/RT
when
Ea=0, K=A

23.

24.

25.

(b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.

26.

(a) The carbon-oxygen bond is carbonyl group is composed of one sigma (\(\sigma\)) and one pi (\(\pi\)) bond. The carbon in carbonyl group is sp²-hybridised. Therefore, the three bonds in the carbonyl carbon are planar and trigonal with bond angle of 120°. (A) and (R) both are correct and (R) is the correct explanation of (A).

27.

(d) Assertion is wrong but reason is correct statement.

28.

(c): Aromatic aldehydes and formaldehyde do not contain \(\alpha\)- hydrogen and thus undergo Cannizzaro reaction. Formaldehyde is more reactive than aromatic aldehydes.

29.

(c): Carboxyl group only marginally decreases the electron density at m - position relative to 0 - and p - positions.

30.

(a) : Assertion and reason both are correct statements and reason is correct explanation for assertion.

31.

(d): Aldehydes having a methyl or methylene group in the a-position or more correctly having atleast one hydrogen atom in the \(\alpha\)-position undergo dimerisation in presence of a base at low temperature to form \(\beta\)-hydroxy aldehydes called aldols. As benzaldehyde does not have any \(\alpha\)-hydrogen hence it does not undergoes aldol condensation.

32.

(b): Both carbanions (formed in presence of base) and enol form (formed in presence of an acid) act as nucleophiles and hence add on the carbonyl group of aldehydes and ketones to give aldols.

33.

(a) : Kinetics deals with the reaction mechanism i.e., how the atoms rearrange themselves in the reactant molecules in a single step or a number of steps, finally leading to the product molecules.

34.

(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.

35.

(a) : Hydrolysis of cane sugar is pseudo first order reaction. Since, water is always in excess, rate of reaction does not depend appreciably on its concentration, thus it is an example of pseudo unimolecular reactions.

36.

(a) : Rate of any reaction is equal to the rate of its slowest step and here rate of given reaction = k [N₂O₅ ] because the slowest step has only one N₂O₅ molecule involved.

37.

(b) : In a heterogeneous system, the reactant is absorbed on the surface of a solid catalyst. The fraction of the surface of the catalyst covered by the reactant is proportional to its concentration at low values and the rate of reaction is first order. However at higher concentration, the surface of catalyst is fully covered and the reaction rate becomes independent of concentration and it becomes zero order reaction.

38.

(a) Carboxylic acids are higher boiling liquids than aldehydes, ketones and even alcohols of comparable molecular masses. This is due to more extensive association of carboxylic acid molecules through intermolecular hydrogen bonding. Hence, both (A) and (R) are correct and (R) is the correct explanation of (A).

39.

(c) The acidity of \(\alpha\)-hydrogen atoms of carbonyl compounds is due to the strong electron withdrawing effect of the carbonyl group and resonance stabilisation of the conjugate base.

Hence, (A) is correct but (R) is incorrect.

40.

(a) A positive catalyst increases rate of reaction by making a new and more efficient mechanism. Thus, both (A) and (R) are correct and (R) is the correct explanation of (A).