The rate constant for a first order reaction is 1 . 15 × 10 - 3 s - 1 . How much time will be taken to reduce the amount of reactants from 5 gm to 3 gm ?

Given a first order reaction with, k = 1 . 15 × 10 - 3 s - 1 Initial weight = 5 gm Weight after time 't' = 3 gm From the integrated rate equation for first order reaction: t = 2 . 303 k log R 1 R 2 = 2 . 303 1 . 15 × 10 - 3 log 5 3 = 2 . 303 1 . 15 × 10 - 3 × 0 . 2219 ⇒ 444 sec The time taken for the required conversion is 444 seconds.

For the decomposition of azoisopropane to hexane and nitrogen at 543 K , the following data are obtained : t ( sec ) P ( mm of Hg ) 0 35 . 0 360 54 . 0 720 63 . 0 Calculate the rate constant.

The reaction is: CH 3 2 CHN = NCH CH 3 2 → C 6 H 14 + N 2 At time t = 0 P 0 0 0 At time t = t P 0 - P P P The total pressure after time t is P total = P 0 - P + P + P = P 0 + P ⇒ P = P total - P 0 Hence, P 0 - P = 2 P 0 - P total From integrated rate equation for first order reaction: k = 2 . 303 t log P 0 P 0 - P = 2 . 303 t log P 0 2 P 0 - P total For time t = 360 sec , k 1 = 2 . 303 360 log 35 2 35 - 54 = 2 . 175 × 10 - 3 sec - 1 For time t = 720 sec , k 2 = 2 . 303 720 log 35 2 35 - 63 = 2 . 235 × 10 - 3 sec - 1 Therefore, the average value of rate constant is : k = k 1 + k 2 2 = 2 . 175 + 2 . 235 × 10 - 3 2 k = 2 . 205 × 10 - 3 sec - 1

For the chemical reaction N 2 g + 3 H 2 g ⇋ 2 N H 3 g , the correct option is:

- d [ N 2 ] d t = 1 2 d [ N H 3 ] d t

- 1 3 d [ H 2 ] d t = - 1 2 d [ N H 3 ] d t

- d [ N 2 ] d t = 2 d [ N H 3 ] d t

3 d [ H 2 ] d t = 2 d [ N H 3 ] d t

MEDIUM

12th Tamil Nadu Board

IMPORTANT

Earn 100

What is an elementary reaction? Give the differences between order and molecularity of a reaction.

Important Questions on Chemical Kinetics

HARD

12th Tamil Nadu Board

IMPORTANT

Chemistry Crash Course (Based on Revised Syllabus-2023)>Chapter 7 - Chemical Kinetics>Exercise>Q 12

The rate constant for a first order reaction is

1.15 \times 10^{- 3} s^{- 1}

. How much time will be taken to reduce the amount of reactants from

5 gm

3 gm

HARD

12th Tamil Nadu Board

IMPORTANT

Chemistry Crash Course (Based on Revised Syllabus-2023)>Chapter 7 - Chemical Kinetics>Exercise>Q 13

The rate constant for a first order reaction is

60 s^{- 1}

. How much time will it take to reduce the initial concentration of the reactant to its

1 / 16^{th}

value?

HARD

12th Tamil Nadu Board

IMPORTANT

Chemistry Crash Course (Based on Revised Syllabus-2023)>Chapter 7 - Chemical Kinetics>Exercise>Q 14

For a first order reaction, show that time required for

99 %

completion is twice the time required for the completion of

90 %

of reaction.

HARD

12th Tamil Nadu Board

IMPORTANT

Chemistry Crash Course (Based on Revised Syllabus-2023)>Chapter 7 - Chemical Kinetics>Exercise>Q 15

For the decomposition of azoisopropane to hexane and nitrogen at $543 K$ , the following data are obtained :

$t (\sec)$	$P (mm of Hg)$
$0$	$35.0$
$360$	$54.0$
$720$	$63.0$

Calculate the rate constant.

HARD

12th Tamil Nadu Board

IMPORTANT

Chemistry Crash Course (Based on Revised Syllabus-2023)>Chapter 7 - Chemical Kinetics>Exercise>Q 16

Consider a reaction;

A \to Products

, with

k = 2.0 \times 10^{- 2} s^{- 1}

. Calculate the concentration of

A

remaining after

100 s

if the initial concentration of

A

1.0 mol L^{- 1}

HARD

12th Tamil Nadu Board

IMPORTANT

Chemistry Crash Course (Based on Revised Syllabus-2023)>Chapter 7 - Chemical Kinetics>Exercise>Q 17

Benzene diazonium chloride in aqueous solution decomposes according to the equation $C_{6} H_{5} N_{2} Cl \to C_{6} H_{5} Cl + N_{2}$ . 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):	$6$	$12$	$18$	$24$	$30$	$\infty$
Volume 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?

HARD

12th Tamil Nadu Board

IMPORTANT

Chemistry Crash Course (Based on Revised Syllabus-2023)>Chapter 7 - Chemical Kinetics>Exercise>Q 18

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?

HARD

12th Tamil Nadu Board

IMPORTANT

Chemistry Crash Course (Based on Revised Syllabus-2023)>Chapter 7 - Chemical Kinetics>Exercise>Q 19

A first order reaction takes

40

min for

30 %

decomposition. Calculate the

t_{1 / 2}

What is an elementary reaction? Give the differences between order and molecularity of a reaction.

Important Questions on Chemical Kinetics

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