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Ncert Solutions Chemistry Class 12th

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Ncert Solutions Chemistry Class 12th Chemical Kinetics

Consider the graph given in Fig. 4.2. Which of the following options does not show instantaneous rate of reaction at 40^t^hsecond?

I. $\frac{V_{5} - V_{2}}{50 - 30}$

II. $\frac{V_{4} - V_{2}}{50 - 30}$

III. $\frac{V_{3} - V_{2}}{40 - 30}$

IV. $\frac{V_{3} - V_{1}}{40 - 20}$

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alok kumar singh

Contributor-Level 10

This is a Fill in the blanks Type Question as classified in NCERT Exemplar

Ans: Correct option B

Reaction occurring at the smallest time interval is known as instantaneous rate of reaction. For e.g the instantaneous rate of reaction at 40s is the rate of reaction during a small interval of time close to 40s. Volume changes during a small-time interval close to the 40s.

Instantaneous rate can be determined graphically by drawing a tangent on the curve

Instantaneous reaction= $\frac{C h a n g e i n C o n c e n t r a t i o n}{C h a n g e i n t i m e}$

Option B is incorrect since the line travels through the graph but does not link to any of the Y axis lines. As a result, option B is incorrect.

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Ncert Solutions Chemistry Class 12th Chemical Kinetics

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 coefficients of reactants in the balanced chemical equation for a reaction.

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

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alok kumar singh

Contributor-Level 10

This is a Fill in the blanks Type Question as classified in NCERT Exemplar

Ans: Correct option C

Option (c) is the only one of the four assertions that is incorrect. In rate law expression, the order of reaction is equal to the sum of the power of concentration of the reactants.

xA + yB→zC

r = k (A)^x (B)^y

Order x + y

The order of the reactions can also be a fraction. In a balanced chemical equation, the order of reaction may or may not be equal to the total of the stoichiometric coefficients of the reactants.

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Ncert Solutions Chemistry Class 12th Chemical Kinetics

A graph of volume of hydrogen released vs time for the reaction between zinc and dil. HCl is given in Fig. 4.2. Based on this mark the correct option

(I) Average rate upto 40s is $\frac{V_{3} - V_{2}}{40}$

(II) Average rate upto 40 seconds is $\frac{V_{3} - V_{2}}{40 - 30}$

(III) Average rate upto 40 seconds is $\frac{V_{3}}{40}$

(IV) Average rate upto 40 seconds is $\frac{V_{3} - V_{1}}{40 - 20}$

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alok kumar singh

Contributor-Level 10

This is a Fill in the blanks Type Question as classified in NCERT Exemplar

Ans: Correct option C

In the given graph V is the volume in the Y axis and time is in X axis

Zn + dil.HCl→ZnCl₂ + H₂↑

Average rate = 40s

Average rate of reaction = $\frac{C h a n g e i n C o n c e n t r a t i o n o f H_{2}}{C h a n g e i n t i m e}$

$\frac{F i n a l C o n c e n t r a t i o n - I n i t i a l C o n c e n t r a t i o n}{F i n a l t i m e - I n i t i a l T i m e}$

Analyzing the graph line where time and volume intersect.

$\frac{V_{3} - 0}{40 - 0}$

$\frac{V_{3}}{40}$

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Ncert Solutions Chemistry Class 12th Chemical Kinetics

Consider the Arrhenius equation given below and mark the correct option.

k = Ae

A. Rate constant increases exponentially with increasing activation energy and decreasing temperature.

B. Rate constant decreases exponentially with increasing activation energy and decreasing temperature.

C. Rate constant increases exponentially with decreasing activation energy and decreasing temperature.

D. Rate constant increases exponentially with decreasing activation energy and increasing temperature.

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alok kumar singh

Contributor-Level 10

This is a Fill in the blanks Type Question as classified in NCERT Exemplar

Ans: Correct option D

k = Ae - $\frac{E a}{R T}$

From this equation

Kα $\frac{1}{E a}$

When Activation energy Ea decreases, rate constant k

increases.

Hence, Rate constant increases exponentially with decreasing activation energy and increasing temperature.

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Ncert Solutions Chemistry Class 12th Chemical Kinetics

According to Arrhenius equation rate constant k is equal to A^e - . Which of the following options represents the graph of in k vs .

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alok kumar singh

Contributor-Level 10

This is a Fill in the blanks Type Question as classified in NCERT Exemplar

Ans: Correct option A

Arrhenius equation Ae - $\frac{E a}{R T}$

K = rate constant

A= frequency factor

Ea= Activation Energy

R= gas constant

T= temperature

ln k = lnA - $\frac{E a}{R T}$

When the temperature rises, ln falls.

∴ ln kv/s $\frac{1}{T}$ , is a negative slope.

ln A is intercepted by k, and its magnitude decreases with time.

∴ Negative slope is obtained.

When compared to the other possibilities, T is increasing over time, which is incorrect.

ln k = $\frac{- E a}{R}$ $\frac{1}{T}$ + lnA

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Ncert Solutions Chemistry Class 12th Chemical Kinetics

Consider a first order gas phase decomposition reaction given below:

A(g) → B(g) + C(g)

The initial pressure of the system before decomposition of A waspt . After lapse of time 't', total pressure of the system increased by x units and became 't' the rate constant k for the reaction is given as _________.

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alok kumar singh

Contributor-Level 10

This is a Fill in the blanks Type Question as classified in NCERT Exemplar

Ans: Correct option B

Given:

A (g) → B (g) + C (g)

p_i= Initial pressure

(Time) t = 0

A (g) → B (g) + C (g)

p_i→0atm + 0atm

t, (p_i - x)atm

p_t = (p_i - x)atm + x + x = p_i + x

p_A = (p_i- x)

The value of x changes when it is substituted.

p_A = p_i- (p_t - p_i) = 2p_i- p_t

K = $\frac{2.303}{t}$ log $\frac{p_{i}}{2 p_{i} - p_{t}}$

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Ncert Solutions Chemistry Class 12th Chemistry NCERT Exemplar Solutions Class 12th Chapter Ten

Assertion- Nitration of chlorobenzene leads to the formation of m-nitrochlorobenzene

Reason :−NO₂ group is a m-directing group.

(i) Assertion and reason both are correct and reason is correct explanation of assertion.

(ii) Assertion and reason both are wrong statements.

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

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

(v) Assertion and reason both are correct statements but reason is not correct explanation of assertion.

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Payal Gupta

Contributor-Level 10

This is a assertion and reason answer type question as classified in NCERT Exemplar

Because m-nitrochlorobenzene is not a stable molecule, the -NO₂ group is a meta-directing group, and the reactions' products include nitro groups at the o- and p- positions.

Correct Answer: Option (iv)

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Ncert Solutions Chemistry Class 12th Chemistry NCERT Exemplar Solutions Class 12th Chapter Ten

Assertion : Hydrolysis of (−)−2-bromooctane proceeds with inversion of configuration.

Reason : This reaction proceeds through the formation of a carbocation.

(i) Assertion and reason both are correct and reason is correct explanation of assertion.

(ii) Assertion and reason both are wrong statements.

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

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

(v) Assertion and reason both are correct statements but reason is not correct explanation of assertion.

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Payal Gupta

Contributor-Level 10

This is a assertion and reason answer type question as classified in NCERT Exemplar

The S_N² mechanism is demonstrated by the hydrolysis of alkyl halides with inversion of configuration. This is a one-step method that does not need the production of carbocation.

Correct Answer: Option (iii)

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Ncert Solutions Chemistry Class 12th Chemistry NCERT Exemplar Solutions Class 12th Chapter Ten

Assertion- It is difficult to replace chlorine by −OH in chlorobenzene in comparison to that in chloroethane.

Reason: Chlorine-carbon (C−Cl) bond in chlorobenzene has a partial double bond character due to resonance.

(i) Assertion and reason both are correct and reason is correct explanation of assertion.

(ii) Assertion and reason both are wrong statements.

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

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

(v) Assertion and reason both are correct statements but reason is not correct explanation of assertion.

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Payal Gupta

Contributor-Level 10

This is a assertion and reason answer type question as classified in NCERT Exemplar

Due to resonance, a partial double bond character occurs in the bond between the C and Cl atoms in chlorobenzene, and we all know that changing a partial double bond character is more difficult than replacing a single bond as in the C - Cl bond in chloroethane.

Correct Answer: Option (i)

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Ncert Solutions Chemistry Class 12th Chemistry NCERT Exemplar Solutions Class 12th Chapter Ten

Assertion: Aryl iodides can be prepared by reaction of arenes with iodine in the presence of an oxidising agent.

Reason : Oxidising agent oxidises I₂ into HI.

(i) Assertion and reason both are correct and reason is correct explanation of assertion.

(ii) Assertion and reason both are wrong statements.

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

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

(v) Assertion and reason both are correct statements but reason is not correct explanation of assertion.

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Payal Gupta

Contributor-Level 10

This is a assertion and reason answer type question as classified in NCERT Exemplar

Oxidising chemicals such as HIO₃ oxidise HI to I₂ because the presence of HI causes the aryl iodides to revert to arenes in their absence.

Correct Answer: Option (iii)

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