For reaction R → P , in 25 minutes the concentration of reactant changed from 0 . 03 M to 0 . 02 M . Give the average velocity in seconds and minutes.

The average velocity of the reaction is given by: V _ = - ∆ C ∆ t , where ∆ C , ∆ t are change in concentrations from reactants to products and change in time respectively. Given, ∆ t = 25 mins = 1500 s , C 2 = 0 . 02 M , C 1 = 0 . 03 M Substituting in the equation we get: V _ = C 1 - C 2 ∆ t = 0 . 03 - 0 . 02 25 = 4 × 10 - 4 M min - 1 In terms of seconds the average velocity is = 4 × 10 - 4 60 = 6 . 67 × 10 - 6 M sec - 1

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

The half life of a first order reaction is 900 min at 820 K . Estimate its half life at 720 K if the energy of activation of the reaction is 250 kJ mol - 1 .

t 1 2 = 900 min . T 1 = 720 K T 2 = 820 K ( t 1 2 ) 1 = ? k 2 = 0 . 693 t 1 2 = 0 . 693 900 = 0 . 00077 E a = 250 × 10 3 Jmol - 1 log k 2 k 1 = E a 2 . 303 R 1 T 1 - 1 T 2 log 0 . 693 900 × k = 250 × 10 3 2 . 303 × 8 . 314 1 720 - 1 820 0 . 84 - 3 . 94 - log k = 250 × 10 3 2 . 303 × 8 . 314 820 - 720 720 × 820 - 3 . 10 - log k = 2 . 21 log k = - 5 . 31 k = 5 × 10 - 6 minute - 1 ∴ ( t 1 2 ) 1 = 0 . 693 k = 0 . 693 5 × 10 - 6 = 1 . 4 × 10 5 minute

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 ICSE

IMPORTANT

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Graph of half life of zero-order reaction and initial concentration of reactant is a (straight line/parabola).

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Important Questions on Chemical Kinetics

MEDIUM

12th ICSE

IMPORTANT

Chemistry Crash Course (Based on Revised Syllabus-2023)>Chapter 1 - Chemical Kinetics>Exercise>Q 12

For reaction

R \to P

, in

25

minutes the concentration of reactant changed from

0.03 M

0.02 M

. Give the average velocity in seconds and minutes.

HARD

12th ICSE

IMPORTANT

Chemistry Crash Course (Based on Revised Syllabus-2023)>Chapter 1 - Chemical Kinetics>Exercise>Q 14

For the reaction- $2 A + B \to A_{2} B,$

The rate $= k [A] [B]^{2}$ with $k = 2.0 \times 10^{- 6} {mol}^{- 2} L^{2} s^{- 1}$ . Calculate the initial rate of reaction when $[A] = 0.1 mol L^{- 1}$ , $[B] = 0.2 mol L^{- 1}$ . Calculate the rate of reaction after $[A]$ is reduced to $0.06 mol L^{- 1}$ .

HARD

12th ICSE

IMPORTANT

Chemistry Crash Course (Based on Revised Syllabus-2023)>Chapter 1 - Chemical Kinetics>Exercise>Q 18

Consider the reaction

C + D \to

products. The rate of the reaction increases by a factor of

4

when concentration of

C

is doubled. The rate of the reaction is tripled when concentration of

D

is tripled. What is the order of the reaction? Write the rate law.

HARD

12th ICSE

IMPORTANT

Chemistry Crash Course (Based on Revised Syllabus-2023)>Chapter 1 - Chemical Kinetics>Exercise>Q 23

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 ICSE

IMPORTANT

Chemistry Crash Course (Based on Revised Syllabus-2023)>Chapter 1 - Chemical Kinetics>Exercise>Q 25

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 ICSE

IMPORTANT

Chemistry Crash Course (Based on Revised Syllabus-2023)>Chapter 1 - Chemical Kinetics>Exercise>Q 33

The half life of a first order reaction is

900 \min

820 K

. Estimate its half life at

720 K

if the energy of activation of the reaction is

250 kJ {mol}^{- 1}

HARD

12th ICSE

IMPORTANT

Chemistry Crash Course (Based on Revised Syllabus-2023)>Chapter 1 - Chemical Kinetics>Exercise>Q 34

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

HARD

12th ICSE

IMPORTANT

Chemistry Crash Course (Based on Revised Syllabus-2023)>Chapter 1 - Solved Chemistry Paper-2>Exercise>Q 24

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?

Graph of half life of zero-order reaction and initial concentration of reactant is a (straight line/parabola).

Important Questions on Chemical Kinetics

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