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Chemical Kinetics is a crucial chapter in Class 12 Chemistry syllabus that deals with the rate of chemical reactions, the factors affecting them, and the mechanisms by which reactions occur. This chapter is numerical-heavy and conceptual, forming the backbone of both board exam questions and competitive exams like JEE and NEET.
These notes are curated to simplify key concepts like rate laws, order of reaction, activation energy, Arrhenius equation, and integrated rate equations for different orders. Download and revise these notes to master the core formulas, derivations, and tricks.
This study material for Class 12 explains the basics of Chemical Kinetics in an easy-to-understand way. Download the PDF to learn key concepts and prepare well for your exams.
Below we have provided the links to downloadable PDFs of class 12 chemistry Ch 4 notes and get an in-depth explanation and understanding of the chapter.
The change in concentration of reactants or products per unit time.
Rate Law:
Rate = k[A]^m[B]^n
Where:
Order of Reaction: Sum of powers of concentration terms in rate law (m+n).
Rate = k
[A] = [A]₀ – kt
Graph: [A] vs t is a straight line.
Unit of k: mol L⁻¹ s⁻¹
Rate = k [A]
ln[A] = ln [A]₀ – kt
Or
k = (2.303 / t) × log ( [A]₀ / [A] )
Half-life (t½) = 0.693/k
Unit of k: s⁻¹
Rate = k[A]²1 / [A] = 1 / [A]₀ + ktHalf-life (t½) = 1 / ( k [A]₀ )Unit of k: L mol⁻¹ s⁻¹
Shows the effect of temperature on rate constant: k = Ae^(-Ea/RT)
Where:
Taking logarithm:
log k = log A – (Ea / 2.303RT)
Arrhenius plot: log k vs 1/T gives a straight line with slope = –Ea / 2.303R
Q: Define rate of a reaction.
Ans: Rate of a reaction is the change in concentration of a reactant or product per unit time.
Q: Write the unit of rate constant for a first-order reaction.
Ans: The unit of rate constant for a first-order reaction is s⁻¹.
Q: What is the half-life formula for a zero-order reaction?
Ans: Half-life for a zero-order reaction: t ½ = [ R0 ] / 2k
Q: Differentiate between order and molecularity.
Ans: Order is the sum of powers of concentration terms in the rate law; molecularity is the number of reacting species involved in an elementary step.
Q: Derive the expression for rate constant of a first-order reaction.
Ans: For A → Product
Q: Define activation energy and its significance.
Ans: Activation Energy (Ea) is the minimum energy required for reactants to convert into products. It determines the reaction speed—higher Ea means slower reaction.
Q: Explain the derivation of integrated rate law for a zero-order and first-order reaction.
Ans:
Q: What is Arrhenius equation? Show how Ea can be calculated from a plot.
Ans: The Arrhenius equation connects the rate constant of a chemical reaction to temperature and activation energy. It is a mathematical relationship that describes how the rate constant (k) varies with temperature and activation energy (Ea).
The Arrhenius equation is: k = A * e^(-Ea/RT)
Activation energy (Ea) can be determined from an Arrhenius plot by calculating the slope of the line when plotting ln(k) against 1/T.
Q: Describe the factors influencing rate of chemical reactions with examples.
Ans: Factors Influencing Rate of Reaction:
🚫 Confusing order of reaction with molecularity.
🚫 Using wrong units for rate constant (k) for different orders.
🚫 Ignoring log vs ln in integrated rate laws.
🚫 Forgetting to convert Celsius to Kelvin in Arrhenius calculations.
🚫 Mixing up rate law with stoichiometric coefficients in balanced reactions.
Chemical Kinetics is all about understanding the "how fast" and "why fast" of chemical reactions. With these well-structured Class 12 notes, you’ll grasp not only the formulas but also their real-world applications. Whether you're a visual learner or a number cruncher, having organized notes helps consolidate your learning effectively and confidently tackle both board and entrance exam questions.
Answer: Chemical kinetics is the branch of chemistry that deals with the study of the speed or rate of chemical reactions and the factors that influence it. It involves understanding how different conditions like temperature, concentration, and catalysts affect reaction rates.
Answer: The rate of a chemical reaction refers to the change in concentration of a reactant or product per unit time. In simple terms, it measures how fast or slow a reaction occurs.
Answer: Several factors can influence the rate of a reaction, including:
Answer: Activation energy is the minimum energy required to start a chemical reaction. It is the energy needed to break bonds in the reactants so that new bonds can form in the products.
Answer: A catalyst is a substance that speeds up a chemical reaction without being consumed in the process. It works by lowering the activation energy, making the reaction proceed faster, but it is not used up in the reaction.
Answer: The order of a reaction refers to the relationship between the concentration of reactants and the rate of the reaction:
Answer: Half-life is the time required for half of the reactant in a reaction to be consumed or to decrease to half of its initial concentration. It is an important concept in reactions that follow first-order kinetics.
Answer: The rate-determining step is the slowest step in a multi-step chemical reaction. This step controls the overall rate of the reaction because it takes the longest time.
Answer: The Arrhenius equation is a formula used to express the dependence of reaction rate on temperature. While it involves some specific terms, the basic idea is that the reaction rate increases with temperature due to higher energy, making the reactants more likely to overcome the activation energy.
Answer: The collision theory suggests that for a reaction to occur, the reactant molecules must collide with each other with sufficient energy and proper orientation. More frequent and energetic collisions increase the chances of a successful reaction.