NCERT Intext Questions 3.1 to 3.9 from Chapter 4 – Chemical Kinetics (Class 12)

 

NCERT Intext Questions 3.1 to 3.9 from Chapter 4 – Chemical Kinetics (Class 12) along with their correct and detailed answers:

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NCERT Class 12 Chemistry – Chapter 4: Chemical Kinetics

Intext Questions (Q3.1 to Q3.15)

Q3.1
From the rate expressions, determine the order of reaction and the dimensions of the rate constant.

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Q3.2
For the reaction $2A + B \rightarrow A_2B$ with rate = $k[A][B]^2$ and $k = 2.0\times10^{-6}\ \text{mol}^{-2}\ \text{L}^2\ \text{s}^{-1}$, calculate the rate when:

• (i) [A] = 0.1 mol/L and [B] = 0.2 mol/L

• (ii) [A] = 0.06 mol/L and [B] = 0.2 mol/L

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Q3.3
Ammonia decomposition (zero-order): $2NH_3 \rightarrow N_2 + 3H_2$
Given: $k = 2.5 \times 10^{-4}\ \text{mol L}^{-1} \text{s}^{-1}$.
Calculate the rate of decomposition of NH₃, and the rates of formation of N₂ and H₂.

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Q3.4
The decomposition of CH₃OCH₃ follows:
$\text{Rate} = k[P_{CH_3OCH_3}]^{3/2}$.
If pressure is expressed in bar and time in minutes, what will be the units of rate constant $k$?

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Q3.5
List the factors affecting the rate of a chemical reaction.

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Q3.6
For a second-order reaction ($\text{Rate} \propto [R]^2$):
(i) What happens to the rate if [R] is doubled?
(ii) What happens to the rate if [R] is halved?

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Q3.7
Explain the effect of temperature on rate constant using the Arrhenius equation.

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Q3.8
For a pseudo first-order reaction, calculate the average rate from $t = 30 \, \text{s}$ to $t = 60 \, \text{s}$ given:
$[A]_{30} = 0.31 \, \text{mol/L}, \ [A]_{60} = 0.17 \, \text{mol/L}$.

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Q3.9
Given: Rate = $k[A]^1[B]^2$
(i) Write the rate law expression.
(ii) If [B] is tripled, by what factor does the rate change?
(iii) If [A] and [B] both are doubled, by what factor does the rate change?

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Q3.10
From the following data, determine the order of reaction with respect to A and B:

[A] (mol/L)	[B] (mol/L)	Initial Rate (mol L⁻¹ s⁻¹)
0.20	0.30	5.07 × 10⁻⁵
0.20	0.10	5.07 × 10⁻⁵
0.40	0.05	1.43 × 10⁻⁴

Q3.11
From the following data, determine the order of reaction with respect to A and B and calculate the rate constant:

Exp.	[A] (mol/L)	[B] (mol/L)	Rate (mol L⁻¹ min⁻¹)
I	0.1	0.1	6.0 × 10⁻³
II	0.3	0.2	7.2 × 10⁻²
III	0.3	0.4	2.88 × 10⁻¹
IV	0.4	0.1	2.40 × 10⁻²

Q3.12
A reaction is first-order in A and zero-order in B. Complete the following table:

Exp.	[A]	[  B]	Rate
I	0.1	0.1	2.0 × 10⁻²
II	0.2	0.2	?
III	0.4	0.4	?
IV	0.1	0.2	?

Q3.13
For a first-order reaction, calculate the half-life period $t_{1/2}$ for:
(i) $k = 200 \, \text{s}^{-1}$.
(ii) $k = 2 \, \text{min}^{-1}$.
(iii) $k=4{\text{yr}}^{-\mathrm{1 \; }}$

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Q3.14
A radioactive sample of $^{14}C$ has a half-life of 5730 years. Calculate the age of a sample in which only 80% of the original $^{14}C$ is left undecayed.

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Q3.15
For the decomposition of $N_2O_5$, data of concentration vs time is given.
(i) Plot $[N_2O_5]$ vs time.
(ii) Determine the half-life.
(iii) Plot $\log [N_2O_5]$ vs time and comment.
(iv) Write the rate law of the reaction.