Chemical Kinetics MCQs From NCERT [Difficult level:Easy]

 

 Question: | NEET   From NCERT    ||| [Difficult level:Easy] Helpful? Yes. Share and spread a word. 

.A zero order reaction is one:

1. in which reactants do not react

2. in which one of the reactants is in large excess

3. whose rate does not change with time

4. whose rate increases with time

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.Subtopic:  Order,Molecularity and Mechanism |

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 Answer ▽ ✅Verified 

3. whose rate does not change with time

In some reactions, the rate is apparently independent of the reactant concentration. The rates of these zero-order reactions do not vary with increasing nor decreasing reactants concentrations. This means that the rate of the reaction is equal to the rate constant, k, of that reaction. This also means whose rate does not change with time.

 Example: (1) Thermal decompostion of HI on gold surface. (2) Decomposition of ammonia on hot platinum surface

Why zero order reaction is a multistep reaction?

Zero order reactions means the rate of the reaction does not depend on the reactant concentration. But the reactants are converted to product. So this reaction takes place in multiple steps.

Is zero order reaction a single step reaction?

No, a zero order reaction can't be a single step reaction as the no. Of reactants participated into an elementary reaction is only the order of reaction.

Is zero order reaction are complex reaction?

Zero order reactions are complex reactions.

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 Question:  From NCERT  | NEET   ||| [Difficult level:Easy] Helpful? Yes. Share and spread a word. 

.For A+B→C+D, ∆H = -20 kJmol-1 the activation energy of the forward reaction is 85 kJ mol-1. The activation energy for backward reaction is...... kJ mol-1

1. 105

2. 85

3. 40

4. 65

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.Subtopic:  Arrhenius Equation |

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 Answer ▽ ✅Verified 

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 Question:  From NCERT  | NEET   ||| [Difficult level:Easy] Helpful? Yes. Share and spread a word. 

.For the elementary reaction M→ N, the rate of disappearance of M increases by a factor of 8 upon doubling the concentration of M. The order of the reaction with respect to M is-

1. 4

2. 3

3. 2

4. 1

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.Subtopic:  First Order Reaction Kinetic

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 Answer ▽ ✅Verified 

2. 3

Order of reaction is the sum of power of concentration or pressure terms raised in the rate law expression. It can be 0,1,2,3 etc. It can be fractional or negative. It is determined experimentally. Rate of reaction means the speed of reaction with which it takes place.

The elementary reaction M → N for this reaction rate can be written as :-

Rate=[M]n$$$$

Rate =K[M]1− − − Eqn1$$$$

As given in question when concentration of Mbecomes double, the rate of reaction becomes 8 times, then the reaction rate becomes:- 

8 × Rate =k[2M]n− − − −Eqn2$$$$

Now if we divide equation 1 by equation 2
Rate8Rate=K[M]1K[2M]n

Now rate by rate get cancelled and K by k cancel from Numerator and Denominator
After simplify the equation we get
18=12n

2n=8

⇒n=3

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 Question:  From NCERT  | NEET   ||| [Difficult level:Easy] Helpful? Yes. Share and spread a word. 

.K for a zero order reaction is 2 x10-2 mol L-1 sec-1. If the concentration of the reactant after 25 sec is 0.5 M, the initial concentration must have been:

1. 0.5 M

2. 1.25 M

3. 12.5M

4. 1.0 M

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.Subtopic:  Order,Molecularity and Mechanism

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 Answer ▽ ✅Verified 

4. 1.0 M

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 Question:  From NCERT  | NEET   ||| [Difficult level:Easy] Helpful? Yes. Share and spread a word. 

.The rate constant for a second order reaction is 8x10-5 M-1 min-1 . How long will it take a 1M solution to be reduced to 0.5M?

1. 8.665 x 103 minute

2. 8 x 10-5 minute

3. 1.25 x 104 minute

4. 4x10-5 minute

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 Answer ▽ ✅Verified 

3. 1.25 x 104 minute

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 Question:  From NCERT  | NEET   ||| [Difficult level:Easy] Helpful? Yes. Share and spread a word. 

.Select the intermediate in the following reaction mechanism:

O3(g) $\rightleftharpoons$ O2(g) +O(g)

O(g) +O3(g) $\to$ 2O2(g)

1. O3(g)

2. O(g)

3. O2(g)

4. none of these

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 Answer ▽ ✅Verified 

2. O(g)

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.A reactant with initial concentration 1.386 mol litre-1 showing first order change takes 40 minute to become half. If it shows zero order change taking 20 minute to becomes half under the similar conditions, the ratio, K1/K0 for first order and zero order kinetics will be:

1. 0.5 mol-1 litre

2. 1.0 mol/litre

3. 1.5 mol/litre

4. 2.0 mol-1 litre

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 Answer ▽ ✅Verified 

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 Question:  From NCERT  | NEET   ||| [Difficult level:Easy] Helpful? Yes. Share and spread a word. 

.In a first order reaction, the concentration of the reactant is decreased from 1.0 M to 0.25M in 20 minute. The rate constant of the reaction would be:

1. 10min-1

2. 6.931 min-1

3. 0.6931 min-1

4. 0.06931 min-1

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 Answer ▽ ✅Verified 

3. 0.6931 min-1

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 Question:  From NCERT  | NEET   ||| [Difficult level:Easy] Helpful? Yes. Share and spread a word. 

.The rate constant of a first order reaction is 4x10-3 sec-1. At a reactant concentration of 0.02 M, the rate of reaction would be:

1. 8 x 10-5 M sec-1

2. 4 x 10-3 M sec-1

3. 2 x 10-1 M sec-1

4. 4 x 10-1 M sec-1

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 Answer ▽ ✅Verified 

1. 8 x 10-5 M sec-1

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.If concentration of reactants is increased by 'X', the rate constant K becomes:

1. eK/X

2. K/X

3. K

4. X/K

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 Answer ▽ ✅Verified 

3. K

When the concentration of reactants is increased by 'X', the rate constant K becomes K. Rate constant has no relation with the concentration of the reactant. Rate constant is a characteristic constant for a given reaction.

Concentration of reactants is related with rate of reaction. If concentration of reactants is increased, rate of reaction also increases.

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 Question:  From NCERT  | NEET   ||| [Difficult level:Easy] Helpful? Yes. Share and spread a word. 

.For a chemical reaction, A→  products, the rate of reaction doubles when the concentration of A is increased by 4 times. The order of the reaction is 

1. 4

2. 0

3. 1/2

4. 1

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 Answer ▽ ✅Verified 

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 Question:  From NCERT  | NEET   ||| [Difficult level:Easy] Helpful? Yes. Share and spread a word. 

.The activation energy of a reaction is zero. The rate constant of the reaction is :

(1) increases with increase in temperature

(2) decreases with decrease in temperature

(3) decreases with increase in temperature

(4) is nearly independent of temperature

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 Answer ▽ ✅Verified 

4) is nearly independent of temperature

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 Question:  From NCERT  | NEET   ||| [Difficult level:Easy] Helpful? Yes. Share and spread a word. 

.For a first-order reaction, the time required for 99.9% of the reaction to take place is nearly :

(1) 10 times that required for half of the reaction

(2) 100 times that required for two-third of the reaction

(3) 10 times that required for one-fourth of the reaction

(4) 20 times that required for half of the reaction

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 Answer ▽ ✅Verified 

1) 10 times that required for half of the reaction

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 Question:  From NCERT  | NEET   ||| [Difficult level:Easy] Helpful? Yes. Share and spread a word. 

.The rate constant for a chemical reaction that takes place at 500 K, is expressed as K = A e-1000. The activation energy of the reaction is-

1. 100 cal/mol

2. 1000 kcal/mol

3. 104 kcal/mol

4. 106 kcal/mol

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 Answer ▽ ✅Verified 

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 Question:  From NCERT  | NEET 2017   ||| [Difficult level:Easy] Helpful? Yes. Share and spread a word. 

.A first order reaction has a specific reaction rate of 10-2s-1. How much time will it take for 20 g of the reactant to reduce to 5 g?

(a) 238.6 s     

 (b) 138.6 s       

 (c) 346.5  s     

   (d) 693.0 s

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 Answer ▽ ✅Verified 

b) 138.6 s     

$t=\frac{2.303}{k}log\left(\frac{a}{a-x}\right)$

$t=\frac{2.303}{10^{-2}/s}log\left(\frac{20g}{5g}\right)$

$t=138.6$ sec

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 Question:  From NCERT  | NEET 2015   ||| [Difficult level:Easy] Helpful? Yes. Share and spread a word. 

.The activation energy of a reaction can be determined from the slope of the graph between : 

1. ln K vs T

2. ln $\frac{K}{T}$ vs T

3. ln K vs $\frac{1}{T}$

4. $\frac{T}{\ln K}vs\frac{1}{T}$

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 Answer ▽ ✅Verified 

3. ln K vs $\frac{1}{T}$

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