CBSE Class 12 Chemistry Chemical Kinetics Worksheet Set 04

Class 12 Chemistry Practice Set: Unit 3 Chemical Kinetics

Review targeted practice sets for Class 12 Chemistry Unit 3 Chemical Kinetics. Built according to official educational guidelines for the 2026-27 academic year, these downloadable worksheets support daily revision and core concept reinforcement.

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Question. (i) What is the order of the reaction whose rate constant has same units as the rate of reaction ?
(ii) For a reaction A + H2O → B; Rate ∝ [A]. What is the order of this reaction?
Answer. (i) Zero order
(ii) Pseudo-first order

Question. State a condition under which a bimolecular reaction is kinetically first order reaction. 
Answer. Let us take a bimolecular reaction :
A + B → Product
Rate = k [A] [B]
When concentration of [B] is taken in excess then rate law will become:
Rate = k [A]
where, k = constant
The rate depends only on one of the reactant as there is negligible change in its concentration so it is bimolecular but is of first order.

Question. (i) For which reaction, the rate of reaction does not decrease with time?
(ii) What is the order of photochemical reaction?
Answer. (i) For zero order reaction the rate of reaction does not decrease with time because it does not depend on concentration of reactants.
(ii) Zero Order reaction.

Question. Explain the following terms:
(i) Rate constant (k)
(ii) Half-life period of reaction (t1/2).
Answer. (i) Rate constant (k): Rate constant is rate of the reaction when the concentration of reactants is unity.
(ii) Half-life period of a reaction (t1/2): Half-life of a reaction is the time in which the concentration of a reactant is reduced to half of its original value.

Question. (i) Explain why H2 and O2 do not react at room temperature.
(ii) Write the rate equation for the reaction
A2 + 3B2 → 2C, if the overall order of the reaction is zero. 
Answer. (i) Due to high activation energy of the reaction between O2 and H2.
(ii) Rate = k [A2]0[B2]0

Question. (i) The rate of reaction decreases with the progress of reaction. Why?
(ii) Reactions having molecularity more than three occur rarely. Why? 
Answer. (i) The rate of reaction depends on the concentration of reactants. Since, the concentration of reactants decreases with time, so rate of reaction also decreases.
(ii) It is because of the fact that collision of more than three molecules is not possible at a time.

Question. (i) What is the order of the reaction whose rate constant has same units as the rate of reaction ?
(ii) For a reaction A + H2O → B; Rate ∝ [A].
What is the order of this reaction ?
Answer. (i) Zero order 
(ii) Pseudo-first order

 

CHEMICAL KINETICS
 
1. Why does the rate of a reaction not remain constant throughout the reaction process? (2010)
 
2. The rate of a reaction is 1.2 x 10-3 L/mol/s. What is the order of the reaction?
 
3. Define the following terms :
 
a) Half-life of a reaction (t½)
b) Rate constant (k) (2015)
 
4. A first order decomposition reaction takes 40 minutes for 30% decomposition. Calculate its t1/2 value. (2008)
 
5. Show that for a first order reaction, the time required for half the change is independent of initial concentration. (2010)
 
6. A reaction is first order in A and second order in B.
a) Write differential rate equation.
b) How is the rate affected when the concentration of A is tripled?
How is the rate affected when the concentration of both A and B are doubled?
 
7. An artifact containing wood has only 80% of the C14 activity found in a living tree. Estimate the age of the artifact if t1/2 of C14 is 5730 years.
 
8. The time required for 10% completion of a first order reaction at 298 K is equal to that required for its 25% completion at 308K.if the value of A is 4 x 1010/s, calculate k at 318K and Ea
 
9. (a) For a reaction A + B → P, the rate is given by Rate = k[A]2[B]
(i) How is the rate of reaction affected if the concentration of A is doubled?
(ii) What is the overall order of reaction if B is present in large excess?
(b) A first order reaction takes 23.1 minutes for 50% completion. Calculate the time required for 75% completion of this reaction.
(Given : log 2 = 0.301, log 3 = 0.4771, log 4 = 0.6021)
 
10. a) Explain the following terms:
i) Order of reaction
ii) Molecularity of a reaction
b) The rate of a reaction increases four times when the temperature changes from 300K to 320K. Calculate the energy of activation of the reaction assuming that it does not change with temperature. (R = 8.314 J K-1 mol-1)
 
11.Time required to decompose SO2Cl2 to half of its initial amount is 60 minutes. If the decomposition is a first order reaction, calculate the rate constant of the reaction.
 
12.The following results have been obtained during the kinetic studies of the reaction: 2A + B → C + D

CBSE Class 12 Chemistry Chemical Kinetics Worksheet Set A 1

Determine the rate law and rate constant for the reaction.
 
13.For the decomposition of azoisopropane into hexane and nitrogen at 543K , the following data were obtained. Calculate the rate constant.
 
T(sec)                 P (mm of Hg)
  0                          35
  360                      54
  720                      63

 

Please click on below link to download CBSE Class 12 Chemistry Chemical Kinetics Worksheet Set A

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Practice Worksheet and Study Resources for Class 12 Chemistry Unit 3 Chemical Kinetics

Download Practice Sheet: Unit 3 Chemical Kinetics (Class 12 Chemistry)

Access structured practice worksheets for Unit 3 Chemical Kinetics designed in alignment with the latest CBSE curriculum for Class 12 Chemistry. These printable problem sets help students build accuracy and prepare effectively for school tests.

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