CBSE Class 12 Chemistry Chemical Kinetics Notes Set 04

Official Class 12 Chemistry Revision Material: CBSE Class 12 Chemistry Chemical Kinetics Notes Set 04

Access comprehensive revision notes for Unit 3 Chemical Kinetics using the CBSE Class 12 Chemistry Chemical Kinetics Notes Set 04. Designed to align with the 2026-27 academic syllabus for Class 12 Chemistry, these concept summaries help students streamline their exam preparation and review complex topics efficiently.

Chapter-wise Concept Summaries: Unit 3 Chemical Kinetics

Access the complete concept summary PDF for Unit 3 Chemical Kinetics below. Regular review of these targeted notes builds familiarity with complex Class 12 Chemistry themes and helps secure higher marks in final school evaluations.

CHEMICAL KINETICS

CONCEPT

Thermodynamics helps us to predict the feasibility of chemical reaction by using ΔG as parameter but it cannot tell everything about the rate of reaction. Rate of chemical reaction is studied in another branch of chemistry called Chemical Kinetics.

Chemical kinetics- The branch of physical chemistry which deals with the study of rate of reaction and their mechanism is called chemical kinetics.

Rate of chemical reaction- The change in concentration of any reactant or product per unit time is called rate of reaction.

TYPES OF RATE OF REACTION-

1. Average rate of reaction- The rate of reaction measured over the long time interval is called average rate of reaction.

Avg rate Δx/Δt = -Δ[R]/Δt = +Δ[p]/Δt

2. Instantaneous rate of reaction- The rate of reaction measured at a particular time is called instantaneous rate of reaction.

Instantaneous rate dx/dt= -d[R]/dt=+d[P]/dt

FACTORS AFFECTING RATE OF REACTION-

1. Concentration of reactant

2. Surface area

3. Temperature

4. Nature of reactant

5. Presence of catalyst

6. Radiation

RATE CONSTANT (k)- It is equal to the rate of reaction when molecular concentration of reactant is at unity.

RATE LAW- The rate of reaction is directly proportional to the product of concentration of reactant and each concentration is raised to some power which may or may not be equal to stereochemistry experimentally.

For a reaction

aA+bB → cC+dD

Rate law = k[A]p[B]q                             Where powers P and Q are determined experimentally

MOLECULARITY – The total no. of reactants taking part in elementary chemical reaction is called molecularity.

ORDER OF REACTION- The sum of powers to which the concentrations terms are raised in a rate law expression is called order of reactions. For above case order = P+Q: orders of rn is determined experimentally

HALF-LIFE PERIOD- The time during which the concentration of the reactant is reduced to half of its initial concentration is called half-life period.

ACTIVATION ENERGY- The minimum extra amount of energy absorbed by reactant molecules so that their energy becomes equal to the threshold energy is called activation energy.

Activation energy = Threshold energy – kinetic energy

TEMPERATURE COEFFICIENT- The ratio of rate constant at two temperatures having difference of 100C is called temperature coefficient.

Temperature coefficient = Rate constant at T+100C/Rate constant at T0C

Arhenius Equation-

K= Ae-Ea/RT

K-rate constant

A-Arrhenius energy

Ea-Activation energy

R- Rate constant

T-Temperature

Log K = Log A- Eq / 2.303RT

Energy of activation can be evaluated as

1. Log [K2/K1] = Ea(1/T1-1/T2)/ 2.303RT

Log [K2/K1] = Ea(1/T1-1/T2)/ 19.15

 

1 MARKS QUESTION
 
1. The gas phase decomposition of acetaldehyde CH3CHO → CH4+CO Follows the rate law.
What are the units of its rate constant. 
Ans. Atm-1/2sec-1 
 
2. State the order with respect to each reactant and overall reaction. 
H2O + 3I- + 2H+ → 2H2O + I3-
Rate = k[H2O2]1[I-]1
Ans. Order of reaction= 1+1= 2

3. Give one example of pseudo first order reaction.

Ans. Hydrolysis of an ester 

CH3COOC2H5 + H2O → CH3COOH + C2H5OH
 
4. The conversion of molecules X to Y follows the second order of kinetics. If concentration of X is increased 3 times, how will it affect the rate of formation of Y. 
Ans. Rate = k [A] 2 
= k [3A] 2 
= k [9a] 2 
The rate of formation will become nine times. 
 
5. The rate law for a reaction is 
Rate = K [A] [B] 3/2 
Can the reaction be an elementary process? Explain. 
Ans. No, an elementary process would have a rate law with orders equal to its molecularities and therefore must be in integral form. 
 
6. What do you understand by ‘rate of reaction’? 
 
7. Name the factors on which the rate of a particular reaction depends. 
 
8. Why rate of reaction does not remain constant throughout? 
 
9. Define specific reaction rate or rate constant.

 

10. What is half-life period of a reaction?

 

 
2 MARKS QUESTION

 

1. The rate of a particular reaction quadruples when the temperature changes from 293K to 313K. Calculate activation energy.

 

Ans. K2/K1 = 4,

 

T1= 293K T2 = 313K

 

Log [K2/K1] = Ea[T2-T1]/19.15

 

Thus on calculating and substituting values we get…..

 

Ea = 52.86 KJ mol-1

 

2. If the decomposition of nitrogen oxide as

 

2N2O5────> 4NO2 + O2

 

follows a first order kinetics.

 

(i) Calculate the rate constant for a 0.05 M solution if the instantaneous rate is 1.5 x 10-6 mol/l/s?

 

Ans. Rate = K [N2O5]
CBSE Class 12 Chemistry notes and questions for Chemical Kinetics Part B 1
 

 

 

3) Write the difference between order and molecularity of reaction.

 

CBSE Class 12 Chemistry notes and questions for Chemical Kinetics Part B 2
 
4) Define Threshold energy and activation energy. How they are related?
Ans. Threshold Energy: It is the minimum amount of energy which the reactant molecules must possess for the effective collision in forming the products.
Activation Energy: It is the excess energy required by the reactants to undergo chemical reaction.
Activation energy = Threshold energy – Average kinetic energy of molecules.
 
 

 Please click the link below to download pdf file for CBSE Class 12 Chemistry notes and questions for Chemical Kinetics Part B.

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Study Material and Revision Notes for Class 12 Chemistry Unit 3 Chemical Kinetics

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