#### Online Mock Tests

#### Chapters

Chapter 2: p-Block Elements - I

Chapter 3: p-Block Elements - II

Chapter 4: Transition and Inner Transition Elements

Chapter 5: Coordination Chemistry

Chapter 6: Solid State

Chapter 7: Chemical Kinetics

Chapter 8: Ionic Equilibrium

Chapter 9: Electro Chemistry

Chapter 10: Surface Chemistry

Chapter 11: Hydroxy Compounds and Ethers

Chapter 12: Carbonyl Compounds and Carboxylic Acids

Chapter 13: Organic Nitrogen Compounds

Chapter 14: Biomolecules

Chapter 15: Chemistry in Everyday Life

## Solutions for Chapter 7: Chemical Kinetics

Below listed, you can find solutions for Chapter 7 of Tamil Nadu Board of Secondary Education Tamil Nadu Board Samacheer Kalvi for Class 12th Chemistry Volume 1 and 2 Answers Guide.

### Tamil Nadu Board Samacheer Kalvi solutions for Class 12th Chemistry Volume 1 and 2 Answers Guide Chapter 7 Chemical Kinetics Evaluation [Pages 226 - 231]

#### Choose the best answer

For a first-order reaction \[\ce{A -> B}\] the rate constant is x min^{−1}. If the initial concentration of A is 0.01 M, the concentration of A after one hour is given by the expression.

0.01 e

^{−x}1 × 10

^{−2}(1 − e^{−60x})(1 × 10

^{−2}) e^{−60x}none of these

A zero-order reaction \[\ce{X -> Product}\], with an initial concentration 0.02 M has a half-life of 10 min. if one starts with concentration 0.04 M, then the half-life is

10 s

5 min

20 min

cannot be predicted using the given information

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

Both

and

For a first order reaction \[\ce{A ->Product}\] with initial concentration x mol L^{−1}, has a half life period of 2.5 hours. For the same reaction with initial concentration `("x"/2)` mol L^{−1} the half life is

(2.5 × 2) hours

`(2.5/2)` hours

2.5 hours

Without knowing the rate constant, t

_{1/2}cannot be determined from the given data

For the reaction, \[\ce{2NH3 -> N2 + 3H2}\], if `(-"d" ["NH"_3])/"dt"` = k_{1} [NH_{3}], `("d" ["N"_2])/"dt"` = k_{2} [NH_{3}], `("d" ["H"_2])/"dt"` = k_{3} [NH_{3}] then the relation between k_{1}, k_{2} and k_{3} is

k

_{1}= k_{2}= k_{3}k

_{1}= 3 k_{2}= 2 k_{3}1.5 k

_{1}= 3 k_{2}= k_{3}2 k

_{1}= k_{2}= 3 k_{3}

The decomposition of phosphine (PH_{3}) on tungsten at low pressure is a first-order reaction. It is because the

rate is proportional to the surface coverage

rate is inversely proportional to the surface coverage

rate is independent of the surface coverage

rate of decomposition is slow

For a reaction Rate = `"k" ["acetone"]^(3/2)` then unit of rate constant and rate of reaction respectively is

`("mol L"^-1 "s"^-1)`, `("mol"^((-1)/2) "L"^(1/2) "s"^-1)`

`("mol"^((-1)/2) "L"^(1/2) "s"^-1)`, `("mol L"^-1 "s"^-1)`

`("mol"^(1/2) "L"^(1/2) "s"^-1)`, `("mol L"^-1 "s"^-1)`

`("mol L s"^-1)`, `("mol"^(1/2) "L"^(1/2) "s")`

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

Enthalpy

Activation energy

Entropy

Internal energy

**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 E_{a} = 0

(iii) rate constant k is equal to collision frequency A if E_{a} = ∞

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

(v) a plot of ln (k) vs `(1/"T")` is a straight line with a positive slope.

Correct statements are

(ii) only

(ii) and (iv)

(ii) and (v)

(i), (ii) and (v)

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

(y − x) kJ mol

^{−1}(x + y) J mol

^{−1}(x − y) kJ mol

^{−1}(x + y) × 10

^{3}J mol^{−1}

What is the activation energy for a reaction if its rate doubles when the temperature is raised from 200 K to 400 K? (R = 8.314 JK^{−1}mol^{−1})

234.65 kJ mol

^{−}^{1}434.65 kJ mol

^{−1}2.305 kJ mol

^{−}^{1}334.65 J mol

^{−}^{1}

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

0.125 M

0.215 M

0.25 × 2.303 M

0.05 M

For a first-order reaction, the rate constant is 6.909 min^{−1 }the time taken for 75% conversion in minutes is

`(3/2) log 2`

`(2/3) log 2`

`(3/2) log (3/4)`

`(2/3) log (4/3)`

In a first order reaction \[\ce{x -> y}\]; if k is the rate constant and the initial concentration of the reactant x is 0.1 M, then, the half life is

`((log 2)/"k")`

`(0.693/((0.1) "k"))`

`((ln 2)/"k")`

none of these

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

\[\ce{2A + B -> C + 3D}\]

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 |

rate = k [A]

^{2}[B]rate = k [A] [B]

^{2}rate = k [A] [B]

rate = `"k" ["A"]^(1/2) ["B"]^(3/2)`

**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.

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

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

Assertion is true but reason is false.

Both assertion and reason are false.

The rate constant of a reaction is 5.8 × 10^{−2 }s^{−1}. The order of the reaction is ____________.

First order

Zero order

Second order

Third order

For the reaction \[\ce{N2O5_{(g)} -> 2NO2_{(g)} + 1/2O2_{(g)}}\], the value of rate of disappearance of N_{2}O_{5} is given as 6.5 × 10^{−2} mol L^{−1}s^{−1}. The rate of formation of NO_{2} and O_{2} is given respectively as

(3.25 × 10

^{−}^{2}mol L^{-1}s^{−}^{1}) and (1.3 × 10^{−}^{2}mol L^{−}^{1}s^{−}^{1})(1.3 × 10

^{−}^{2}mol L^{−}^{1}s^{−}^{1}) and (3.25 × 10^{−}^{2}mol L^{−}^{1}s^{−}^{1})(1.3 × 10

^{−}^{1}mol L^{−}^{1}s^{−}^{1}) and (3.25 × 10^{−}^{2}mol L^{−}^{1}s^{−}^{1})None of these

During the decomposition of H_{2}O_{2} to give dioxygen, 48 g O_{2} is formed per minute at certain point of time. The rate of formation of water at this point is

0.75 mol min

^{−1}1.5 mol min

^{−1}2.25 mol min

^{−1}3.0 mol min

^{−1}

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

Zero

One

Fraction

None

In a homogeneous reaction \[\ce{A -> B + C + D}\], the initial pressure was P_{0} and after time t it was P. Expression for rate constant in terms of P_{0}, P and t will be

`"k" = (2.303/"t") log ((2"P"_0)/(3"P"_0 - "P"))`

`"k" = (2.303/"t") log ((2"P"_0)/("P"_0 - "P"))`

`"k" = (2.303/"t") log ((3"P"_0 - "P")/(2"P"_0))`

`"k" = (2.303/"t") log ((2"P"_0)/(3"P"_0 - 2"P"))`

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 ____________.

20 minutes

30 minutes

35 minutes

75 minutes

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

`(1/2) "g"`

`(1/4) "g"`

`(1/8) "g"`

`(1/16) "g"`

The correct difference between first and second order reactions is that

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

The half life of a first order reaction does not depend on [A

_{0}]; the half life of a second order reaction does depend on [A_{0}].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.

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.

After 2 hours, a radioactive substance becomes `(1/16)^"th"` of original amount. Then the half life ( in min) is

60 minutes

120 minutes

30 minutes

15 minutes

#### Answer the following questions:

Define average rate.

Define instantaneous rate.

Define rate law.

Define rate constant.

Derive integrated rate law for a zero-order reaction \[\ce{A -> Product}\].

Define half life of a reaction.

Show that for a first order reaction half life is independent of initial concentration.

What is an elementary reaction?

Give the differences between order and molecularity of a reaction.

Explain the rate determining step with an example.

Describe the graphical representation of first order reaction.

**Write the rate law for the following reaction.**

A reaction that is `3/2` order in x and zero order in y.

**Write the rate law for the following reaction.**

A reaction that is second order in NO and first order in Br_{2}.

Explain the effect of catalyst on reaction rate with an example.

The rate law for a reaction of A, B and C has been found to be rate = `"k" ["A"]^2["B"] ["L"]^(3/2)`. How would the rate of reaction change when

- Concentration of [L] is quadrupled
- Concentration of both [A] and [B] are doubled
- Concentration of [A] is halved
- Concentration of [A] is reduced to `(1/3)` and concentration of [L] is quadrupled.

The rate of formation of a dimer in a second order reaction is 7.5 × 10^{−3} mol L^{−1}s^{−1} at 0.05 mol L^{−1} monomer concentration. Calculate the rate constant.

For a reaction \[\ce{x + y + z -> products}\] the rate law is given by rate = `"k" ["x"]^(3/2) ["y"]^(1/2)` what is the overall order of the reaction and what is the order of the reaction with respect to z.

Explain briefly the collision theory of bimolecular reactions.

Write Arrhenius equation and explains the terms involved.

The decomposition of Cl_{2}O7 at 500 K in the gas phase to Cl_{2} and O_{2} is a first order reaction. After 1 minute at 500 K, the pressure of Cl_{2}O_{7} falls from 0.08 to 0.04 atm. Calculate the rate constant in s^{−1}.

Give two examples for zero order reaction.

Explain pseudo-first-order reaction with an example.

**Identify the order for the following reaction.**

Rusting of Iron

**Identify the order for the following reaction.**

Radioactive disintegration of _{92}U^{238}

**Identify the order for the following reaction.**

\[\ce{2A + 3B -> products}\]; rate = `"k" ["A"]^(1/2) ["B"]^2`

A gas phase reaction has energy of activation 200 kJ mol^{−1}. If the frequency factor of the reaction is 1.6 × 10^{13} s^{−1}. Calculate the rate constant at 600 K. `("e"^-40.09 = 3.8 xx 10^-18)`

For the reaction \[\ce{2x + y -> L}\] find the rate law from the following data.

[x](M) |
[y](M) |
rate(M s^{−1}) |

0.2 | 0.02 | 0.15 |

0.4 | 0.02 | 0.30 |

0.4 | 0.08 | 1.20 |

How do concentrations of the reactant influence the rate of reaction?

How do nature of the reactant influence rate of reaction?

The rate constant for a first order reaction is 1.54 × 10^{−3} s^{−1}. Calculate its half life time.

The half life of the homogeneous gaseous reaction \[\ce{SO2Cl2 -> SO2 + Cl2}\] which obeys first order kinetics is 8.0 minutes. How long will it take for the concentration of SO_{2}Cl_{2} to be reduced to 1% of the initial value?

The time for half change in a first order decomposition of a substance A is 60 seconds. Calculate the rate constant. How much of A will be left after 180 seconds?

A zero order reaction is 20% complete in 20 minutes. Calculate the value of the rate constant. In what time will the reaction be 80% complete?

The activation energy of a reaction is 22.5 k Cal mol^{−1} and the value of rate constant at 40°C is 1.8 × 10^{−5} s^{−1}. Calculate the frequency factor, A.

Benzene diazonium chloride in aqueous solution decomposes according to the equation \[\ce{C6H5N2Cl -> C6H5Cl + N2}\]. Starting with an initial concentration of 10 g L^{−1}, the volume of N_{2} gas obtained at 50°C at different intervals of time was found to be as under:

t (min): |
6 | 12 | 18 | 24 | 30 | ∞ |

Vol. of N_{2}(ml) |
19.3 | 32.6 | 41.3 | 46.5 | 50.4 | 58.3 |

Show that the above reaction follows the first order kinetics. What is the value of the rate constant?

From the following data, show that the decomposition of hydrogen peroxide is a reaction of the first order:

t (min) |
0 | 10 | 20 |

V (ml) |
46.1 | 29.8 | 19.3 |

Where t is the time in minutes and V is the volume of standard KMnO_{4} solution required for titrating the same volume of the reaction mixture.

A first order reaction is 40% complete in 50 minutes. Calculate the value of the rate constant. In what time will the reaction be 80% complete?

## Solutions for Chapter 7: Chemical Kinetics

## Tamil Nadu Board Samacheer Kalvi solutions for Class 12th Chemistry Volume 1 and 2 Answers Guide chapter 7 - Chemical Kinetics

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Concepts covered in Class 12th Chemistry Volume 1 and 2 Answers Guide chapter 7 Chemical Kinetics are Integrated Rate Equations, First Order Reactions, Zero Order Reactions, Rate of a Chemical Reaction, Molecularity, Collision Theory, Arrhenius Equation – the Effect of Temperature on Reaction Rate, Factors Affecting the Reaction Rate, Pseudo First Order Reaction, Half Life Period of a Reaction.

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