Chemical Kinetics Class 12 Notes for CBSE, JEE and NEET

Chemical kinetics tells us how fast a reaction happens and which factors change its speed. These chemical kinetics class 12 notes cover the NCERT chapter in a revision-friendly way for board exams, JEE and NEET. Read the key concepts and formulas below, then use the handwritten pages to practise. eSaral also offers NCERT Solutions, previous year questions, test series and important questions. For the other chapters, see the complete Class 12 Chemistry notes. Download the eSaral app for free study material and video tutorials.

India's Best Exam Preparation for Class 12th - Download Now

Chemical Kinetics Class 12 Notes

India's Best Exam Preparation for Class 12th - Download Now

India's Best Exam Preparation for Class 12th - Download Now

India's Best Exam Preparation for Class 12th - Download Now

India's Best Exam Preparation for Class 12th - Download Now

India's Best Exam Preparation for Class 12th - Download Now

India's Best Exam Preparation for Class 12th - Download Now

Chemical Kinetics Class 12 Notes: Chapter Overview
The chapter covers the rate of a reaction, rate law and rate constant, order and molecularity, integrated rate equations for zero and first order reactions, half-life, and the Arrhenius equation. Together these explain how concentration, temperature and a catalyst affect the speed of a reaction.

India's Best Exam Preparation for Class 12th - Download Now

Rate of Reaction and Rate Law

The rate of reaction is the change in concentration of a reactant or product per unit time. For a reaction aA + bB → cC + dD, rate = −(1/a) d[A]/dt = −(1/b) d[B]/dt = (1/c) d[C]/dt = (1/d) d[D]/dt. The rate law expresses the rate in terms of concentrations: rate = k[A]^x[B]^y, where k is the rate constant. The powers x and y are found by experiment, not from the balanced equation.

Order of Reaction and Molecularity: Key Differences

Order of reaction is the sum of the powers of concentration terms in the rate law (x + y). It is found experimentally and can be zero, a fraction or a whole number. Molecularity is the number of reacting species that collide in an elementary step. It is always a whole number, is never zero, and applies only to elementary reactions. For a complex reaction, the overall order is decided by the slowest step, called the rate-determining step.

Units of Rate Constant for Zero and First Order Reactions

• Zero order: mol L⁻¹ s⁻¹
• First order: s⁻¹
• Second order: L mol⁻¹ s⁻¹

For order n, the unit is (mol L⁻¹)^(1−n) s⁻¹.

Integrated Rate Equations and Half-Life of a First-Order Reaction

Zero order: [R] = [R]₀ − kt, and t₁/₂ = [R]₀/2k. A graph of [R] against t is a straight line with slope −k.
First order: k = (2.303/t) log([R]₀/[R]), and ln[R] = ln[R]₀ − kt. A graph of ln[R] against t is a straight line with slope −k.

Half-Life of First Order Reaction Formula

For a first order reaction, t₁/₂ = 0.693/k. The half-life does not depend on the initial concentration. For example, if k = 0.0693 min⁻¹, then t₁/₂ = 0.693/0.0693 = 10 minutes, whether you start with 1 M or 0.1 M.

Arrhenius Equation: Effect of Temperature and Catalyst

The Arrhenius equation is k = A e^(−Ea/RT), or log k = log A − Ea/(2.303RT). Here A is the frequency factor, Ea is the activation energy, R = 8.314 J mol⁻¹ K⁻¹ and T is in Kelvin. A plot of log k against 1/T is a straight line with slope −Ea/2.303R. For many reactions near room temperature, the rate constant roughly doubles for every 10 K rise. A catalyst lowers the activation energy, so k increases, but it does not change the enthalpy of the reaction or the equilibrium position.

Arrhenius Equation Numericals for JEE

Most numericals use the two-temperature form: log(k₂/k₁) = (Ea/2.303R)(1/T₁ − 1/T₂). You are given two rate constants at two temperatures and asked for Ea, or the other way round. Convert temperature to Kelvin and keep Ea and R in the same units, either J or kJ.

Important Topics in Chemical Kinetics Class 12 Notes for JEE and NEET

Chemical kinetics is a regular chapter in CBSE boards, JEE and NEET. In the current CBSE blueprint it carries about 7 marks, so check the latest blueprint for your year. These chemical kinetics class 12 notes focus on the topics asked most often:

• Units of rate constant and order from the rate law
• Half-life and time-based calculations for first order reactions
• Graphs of concentration against time for zero and first order reactions
• Effect of temperature and catalyst, and Arrhenius numericals
• Rate-determining step and mechanism-based questions, mainly in JEE Advanced

How to Revise Chemical Kinetics Class 12 Notes

• Write the units of k, the integrated equations and the half-life formulas on one page.
• Practise graphs, because many MCQs ask you to identify the order from a plot.
• Solve the exercises of this chapter and compare your steps with the NCERT Solutions for Class 12 Chemistry.

eSaral is a Kota-based platform for JEE, NEET and Class 8–10 preparation, with the mission of making quality education available to every student in India. We hope these chemical kinetics class 12 notes help you remember the key points and revise with confidence. To read notes for every chapter, get the complete Class 12 Chemistry notes, and for video lectures and practice, download the eSaral app.