12th Chemistry - Book Back Answers - Unit 7 Chemical Kinetics - English Medium Guides

  

 

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Tamil Nadu Board 12th Standard Chemistry - Unit 7: Book Back Answers and Solutions

    This post covers the book back answers and solutions for Unit 7 from the Tamil Nadu State Board 12th Standard Chemistry textbook. These detailed answers have been carefully prepared by our expert teachers at KalviTips.com.

    We have explained each answer in a simple, easy-to-understand format, highlighting important points step by step under the relevant subtopics. Students are advised to read and memorize these subtopics thoroughly. Once you understand the main concepts, you’ll be able to connect other related points with real-life examples and confidently present them in your tests and exams.

    By going through this material, you’ll gain a strong understanding of Unit 7 along with the corresponding book back questions and answers (PDF format).

Question Types Covered:

• 1 Mark Questions: Choose the correct answer, Fill in the blanks, Identify the correct statement, Match the following 
• 2 Mark Questions: Answer briefly 
• 3, 4, and 5 Mark Questions: Answer in detail

All answers are presented in a clear and student-friendly manner, focusing on key points to help you score full marks.

All the best, Class 12 students! Prepare well and aim for top scores. Thank you!

I. Multiple Choice Questions

1. For a first order reaction A $\to$ B the rate constant is x min⁻¹  . If the initial concentration of A is 0.01M , the concentration of A after one hour is given by the expression.

a) 0.01 e^−x

b) 1×10⁻² (1−e^−60x )

c) (1×10⁻² )e^−60x

d) none of these

Answer Key:

c) (1×10⁻² )e^−60x 

  

2. A zero order reaction X $\to$ Product , with an initial concentration 0.02M has

a half life of 10 min. if one starts with concentration 0.04M, then the half life is

a) 10 s

b) 5 min

c) 20 min

d) cannot be predicted using the given information

Answer Key:

c) 20 min

  

3. Among the following graphs showing variation of rate constant with temperature (T) for a reaction, the one that exhibits Arrhenius behavior over the entire temperature range is

a) 

b) 

c) 

d) both (b) and (c)

Answer Key:

 

4. For a first order reaction A$\to$ product with initial concentration x mol L⁻¹ , has a half life period of 2.5 hours . For the same reaction with initial concentration  mol L⁻¹ the half life is

a) (2.5 × 2)hours

b) 

c) 2.5 hours

d) Without knowing the rate constant, ${\mathbf{t}}_{\mathbf{1}\mathbf{/}\mathbf{2}}$ cannot be determined from the given data

Answer Key:

c) 2.5 hours

  

5. For the reaction, 2NH₃ $\to$ N₂ + 3H₂

_{$\mathbf{,}\mathbf{i}\mathbf{f}\mathbf{ }\frac{\mathbf{-}\mathbf{d}\mathbf{\left[}\mathbf{N}{\mathbf{H}}_{\mathbf{3}}\mathbf{\right]}}{\mathbf{d}\mathbf{t}}\mathbf{=}{\mathbf{k}}_{\mathbf{1}}\left[{\mathbf{NH}}_{\mathbf{3}}\right]$} 

_{$\frac{\mathbf{d}\mathbf{\left[}{\mathbf{N}}_{\mathbf{2}}\mathbf{\right]}}{\mathbf{d}\mathbf{t}}\mathbf{=}{\mathbf{K}}_{\mathbf{2}}\left[{\mathbf{NH}}_{\mathbf{3}}\right],\frac{\mathbf{d}\mathbf{[}{\mathbf{H}}_{\mathbf{2}\mathbf{]}}}{\mathbf{d}\mathbf{t}}={\mathrm{K}}_3\left[{\mathbf{NH}}_{\mathbf{3}}\right]$} 

then the relation between k₁, k₂ and k₃ is

a) k₁ = k₂ = k₃

b) k₁ = 3 k₂ = 2 k₃

c) 1.5 k₁ = 3 k₂= k₃

d) 2k₁ = k₂ = 3 k₃

Answer Key:

c) 1.5 k₁ = 3 k₂= k₃

  

6. The decomposition of phosphine (PH₃) on tungsten at low pressure is a first

order reaction. It is because the

a) rate is proportional to the surface coverage

b) rate is inversely proportional to the surface coverage

c) rate is independent of the surface coverage

d) rate of decomposition is slow

Answer Key:

a) rate is proportional to the surface coverage

  

7. For a reaction Rate = k$\mathbf{[}\mathbf{a}\mathbf{c}\mathbf{e}\mathbf{t}\mathbf{o}\mathbf{n}\mathbf{e}{\mathbf{]}}^{\raisebox{1ex}{$\mathbf{3}$}\!\left/ \!\raisebox{-1ex}{$\mathbf{2}$}\right.}$ then unit of rate constant and rate of reaction

respectively is

a) $\mathbf{(}\mathbf{m}\mathbf{o}\mathbf{l}\mathbf{ }{\mathbf{L}}^{\mathbf{-}\mathbf{1}}{\mathbf{s}}^{\mathbf{-}\mathbf{1}}\mathbf{)}\mathbf{,}\mathbf{ }\mathbf{\left(}{\mathbf{mol}}^{\raisebox{1ex}{$\mathbf{-}\mathbf{1}$}\!\left/ \!\raisebox{-1ex}{$\mathbf{2}$}\right.}{\mathbf{L}}^{\raisebox{1ex}{$\mathbf{1}$}\!\left/ \!\raisebox{-1ex}{$\mathbf{2}$}\right.}{\mathbf{s}}^{\mathbf{-}\mathbf{1}}\mathbf{\right)}$

b) $\mathbf{\left(}\mathbf{m}\mathbf{o}{\mathbf{l}}^{\raisebox{1ex}{$\mathbf{-}\mathbf{1}$}\!\left/ \!\raisebox{-1ex}{$\mathbf{2}$}\right.}{\mathbf{L}}^{\raisebox{1ex}{$\mathbf{1}$}\!\left/ \!\raisebox{-1ex}{$\mathbf{2}$}\right.}{\mathbf{s}}^{\mathbf{-}\mathbf{1}}\mathbf{\right)}\mathbf{,}\mathbf{ }\mathbf{(}\mathbf{m}\mathbf{o}\mathbf{l}\mathbf{ }{\mathbf{L}}^{\mathbf{-}\mathbf{1}}{\mathbf{s}}^{\mathbf{-}\mathbf{1}}\mathbf{)}$

c) $\mathbf{\left(}{\mathbf{mol}}^{\raisebox{1ex}{$\mathbf{1}$}\!\left/ \!\raisebox{-1ex}{$\mathbf{2}$}\right.}{\mathbf{L}}^{\raisebox{1ex}{$\mathbf{1}$}\!\left/ \!\raisebox{-1ex}{$\mathbf{2}$}\right.}{\mathbf{s}}^{\mathbf{-}\mathbf{1}}\mathbf{\right)}\mathbf{,}\mathbf{ }\mathbf{(}\mathbf{mol}\mathbf{ }{\mathbf{L}}^{\mathbf{-}\mathbf{1}}{\mathbf{s}}^{\mathbf{-}\mathbf{1}}\mathbf{)}$

d) $\mathbf{(}\mathbf{m}\mathbf{o}\mathbf{l}\mathbf{ }\mathbf{L}{\mathbf{s}}^{\mathbf{-}\mathbf{1}}\mathbf{)}\mathbf{,}\mathbf{ }\mathbf{(}{\mathbf{mol}}^{\raisebox{1ex}{$\mathbf{1}$}\!\left/ \!\raisebox{-1ex}{$\mathbf{2}$}\right.}{\mathbf{L}}^{\raisebox{1ex}{$\mathbf{1}$}\!\left/ \!\raisebox{-1ex}{$\mathbf{2}$}\right.}\mathbf{s}\mathbf{ }\mathbf{)}$

Answer Key:

b) $\mathbf{\left(}\mathbf{m}\mathbf{o}{\mathbf{l}}^{\raisebox{1ex}{$\mathbf{-}\mathbf{1}$}\!\left/ \!\raisebox{-1ex}{$\mathbf{2}$}\right.}{\mathbf{L}}^{\raisebox{1ex}{$\mathbf{1}$}\!\left/ \!\raisebox{-1ex}{$\mathbf{2}$}\right.}{\mathbf{s}}^{\mathbf{-}\mathbf{1}}\mathbf{\right)}\mathbf{,}\mathbf{ }\mathbf{(}\mathbf{m}\mathbf{o}\mathbf{l}\mathbf{ }{\mathbf{L}}^{\mathbf{-}\mathbf{1}}{\mathbf{s}}^{\mathbf{-}\mathbf{1}}\mathbf{)}$

$\mathbf{ }$ 

8. The addition of a catalyst during a chemical reaction alters which of the following quantities?

a) Enthalpy

b) Activation energy

c) Entropy

d) Internal energy

Answer Key:

b) Activation energy

  

9. Consider the following statements :

(i) increase in concentration of the reactant increases the rate of a zero order reaction.

(ii) rate constant k is equal to collision frequency A if ${\mathbf{E}}_{\mathbf{a}}$ = 0 a

(iii) rate constant k is equal to collision frequency A if ${\mathbf{E}}_{\mathbf{a}}$=∞

(iv) a plot of ln(k)vs T is a straight line.

(v) a plot of ln k vs  is a straight line with a positive slope.

Correct statements are

a) (ii) only

b) (ii) and (iv)

c) (ii) and (v)

d) (i), (ii) and (v)

Answer Key:

a) (ii) only 

  

10. In a reversible reaction, the enthalpy change and the activation energy in the forward direction are respectively −x kJ mol⁻¹ and y kJ mol⁻¹. Therefore , the energy of activation in the backward direction is

a) (y −x)kJ mol⁻¹

b) (x + y)J mol⁻¹

c) (x −y)kJ mol⁻¹

d) (x + y) × 103 J mol⁻¹

Answer Key:

d) (x + y) × 103 J mol⁻¹

 

11. What is the activation energy for a temperature is raised from 200K to 400K?

(R = 8.314 JK^-1mol^-1)

a) 234.65 kJ mol⁻¹

b) 434.65 kJ mol⁻¹

c) 2.305 kJ mol^-1

d) 334.65 J mol⁻¹

Answer Key:

c) 2.305 kJ mol^-1

  

12.

; This reaction nfollows first order kinetics. The rate constant at particular temperature is 2.303 × 10−2 hour−1. The initial concentration of cyclopropane is 0.25M. What will be the concentration of cyclopropane after 1806 minutes? (log 2 = 0.3010)

a) 0.125M

b) 0.215M

c) 0.25 × 2.303M

d) 0.05M

Answer Key:

a) 0.125M 

  

13. For a first order reaction, the rate constant is 6.909 min-1.the time taken for 75% conversion in minutes is

a) 

b) 

c) 

d) 

Answer Key:

b) 

 

14. In a first order reaction x $\to$y ; if k is the rate constant and the initial

concentration of the reactant x is 0.1M, then, the half life is

a) 

b) 

c) 

d) none of these

Answer Key:

c) 

 

15. Predict the rate law of the following reaction based on the data given below

2A + B  $\to$C + 3D

Reaction number	[A] (min)	[B] (min)	Initial rate (M s-1)
1	0.1	0.1	x
2	0.2	0.1	2x
3	0.1	0.2	4x
4	0.2	0.2	8x

a) rate = k$\mathbf{[}\mathbf{A}{\mathbf{]}}^{\mathbf{2}}$[B]

b) rate = k[A]$\mathbf{[}\mathbf{B}{\mathbf{]}}^{\mathbf{2}}$

c) rate = k[A][B]

d) rate = k$\mathbf{\left[}\mathbf{A}{\mathbf{]}}^{\raisebox{1ex}{$\mathbf{1}$}\!\left/ \!\raisebox{-1ex}{$\mathbf{2}$}\right.}\mathbf{\right[}\mathbf{B}{\mathbf{]}}^{\raisebox{1ex}{$\mathbf{1}$}\!\left/ \!\raisebox{-1ex}{$\mathbf{2}$}\right.}$

Answer Key:

b) rate = k[A]$\mathbf{[}\mathbf{B}{\mathbf{]}}^{\mathbf{2}}$ 

  

16. Assertion: rate of reaction doubles when the concentration of the reactant is doubles if it is a first order reaction.

Reason: rate constant also doubles

a) Both assertion and reason are true and reason is the correct explanation of assertion.

b) Both assertion and reason are true but reason is not the correct explanation of assertion.

c) Assertion is true but reason is false.

d) Both assertion and reason are false.

Answer Key:

c) Assertion is true but reason is false.

  

17. The rate constant of a reaction is 5.8 × 10⁻² s⁻¹ . The order of the reaction is

a) First order

b) zero order

c) Second order

d) Third order

Answer Key:

a) First order 

  

18. For the reaction N₂O₅ $\to$ 2NO₂ (g) + $\frac{\mathbf{1}}{\mathbf{2}}$O₂, the value of rate of disappearance of N₂O₅ is given as 6.5 × 10⁻² mol L⁻¹s⁻¹. The rate of formation of NO₂ and O₂ is given respectively as

a) (3.25 × 10⁻² mol L⁻¹s⁻¹ ) and (1.3 × 10⁻² mol L⁻¹s⁻¹ )

b) (1.3 × 10⁻² mol L⁻¹s⁻¹ ) and (3.25 × 10⁻² mol L⁻¹s⁻¹ )

c) (1.3 × 10⁻¹ mol L⁻¹s⁻¹ ) and (3.25 × 10⁻² mol L⁻¹s⁻¹ )

d) None of these

Answer Key:

c) (1.3 × 10⁻¹ mol L⁻¹s⁻¹ ) and (3.25 × 10⁻² mol L⁻¹s⁻¹ )

 

19. During the decomposition of H₂O₂ to give dioxygen, 48 g O₂ is formed per minute at certain point of time. The rate of formation of water at this point is

a) 0.75 mol min⁻¹

b) 1.5 mol min⁻¹

c) 2.25 mol min⁻¹

d) 3.0 mol min⁻¹

Answer Key:

d) 3.0 mol min⁻¹

 

20. If the initial concentration of the reactant is doubled, the time for half reaction is also doubled. Then the order of the reaction is

a) Zero

b) one

c) Fraction

d) none

Answer Key:

a) Zero 

  

21. In a homogeneous reaction A$\to$B + C + D, the initial pressure was P₀ and after time t it was P. expression for rate constant in terms of P₀, P and t will be

a) k=  $log$

b) k= $$$log$$$

c) k= $log$

d)k= $log$

Answer Key:

a) k=  $log$

 

22. If 75% of a first order reaction was completed in 60 minutes , 50% of the same reaction under the same conditions would be completed in

a) 20 minutes

b) 30 minutes

c) 35 minutes

d) 75 minutes

Answer Key:

b) 30 minutes

  

23. The half life period of a radioactive element is 140 days. After 560 days , 1 g of element will be reduced to

a) g

b) g

c) g

d) g

Answer Key:

d) g

 

24. The correct difference between first and second order reactions is that (NEET)

a) A first order reaction can be catalysed; a second order reaction cannot be catalysed.

b) The half life of a first order reaction does not depend on [A₀]; the half life of a second order reaction does depend on [A₀].

c) The rate of a first order reaction does not depend on reactant concentrations; the rate of a second order reaction does depend on reactant concentrations.

d) The rate of a first order reaction does depend on reactant concentrations; the rate of a second order reaction does not depend on reactant concentrations.

Answer Key:

b) The half life of a first order reaction does not depend on [A₀]; the half life of a second order reaction does depend on [A₀].

  

25. After 2 hours, a radioactive substance becomes  of original amount.

Then the half life ( in min) is

a) 60 minutes

b) 120 minutes

c) 30 minutes

d) 15 minutes

Answer Key:

b) The half life of a first order reaction does not depend on [A₀]; the half life of a second order reaction does depend on [A₀]. 

 

II. Short Answer Questions.

12th Chemistry

III. Long Answer Questions. 

12th Chemistry

IV. Exercise.   

12th Chemistry