Class 12 Chemistry Ch 3 Chemical Kinetics Notes - Download PDF

Class 12 Chemistry Chapter 3 Chemical Kinetics carries 6 to 8 marks in the CBSE Board paper and 4 to 6% weight in JEE Main, placing it among the top scoring physical chemistry chapters of the rationalised 2026-27 NCERT. This page hosts the full revision notes PDF, sub-topic weightage map, important derivations, and the 2025 PYQ trend for boards and entrance exams.

• CBSE Boards: 6 to 8 marks every year, usually one 3-mark numerical on rate constant plus one 5-mark long answer on order, half-life or Arrhenius equation.
• JEE Main: 4 to 6% of the Chemistry paper, with 2 to 3 questions per shift on integrated rate laws, half-life, and the temperature coefficient.
• NEET: 2 to 3 questions per year, almost always from order of reaction, pseudo first-order and Arrhenius-type numericals.

The notes below build the chapter the way examiners actually test it: rate of reaction first, then order and molecularity, then the integrated rate equations for zero and first order, and finally collision and Arrhenius theory. Each sub-topic ends with the formula or graph that CBSE markers actually look for on the answer sheet.

These Collegedunia Chemical Kinetics notes are curated by subject experts, mapped to the 2026-27 NCERT print, and refined against the last five years of CBSE Board, JEE Main, and NEET papers.

Also Check:

• Chemical Kinetics Class 12 Chemistry NCERT Solutions
• Chemical Kinetics Class 12 Chemistry Formula Sheet
• CBSE Class 12 Chemistry Syllabus 2026-27

Most Important Sub-Topics in Chemical Kinetics and Their Mark Distribution

An audit of CBSE, JEE Main and NEET papers from 2021 to 2025 shows the chapter's marks concentrate on a small set of sub-topics. The table below ranks them by frequency of appearance, so revision time can be apportioned correctly.

Chemical Kinetics Video Walkthrough

Source: Magnet Brains on YouTube

Chemical Kinetics Topic-by-Topic Notes for Class 12 Chemistry

Rate sets up order, order sets up the integrated rate law, and the integrated rate law sets up half-life. Arrhenius then explains the temperature dependence of k . Each H3 below follows that order.

Rate of a Chemical Reaction: Average and Instantaneous Rate

For a reaction aA + bB → cC + dD , the rate is the change in concentration per unit time, divided by the stoichiometric coefficient: rate = -1ad[A]dt = +1cd[C]dt . The average rate over an interval is the concentration change divided by elapsed time; the instantaneous rate is the slope of the concentration vs time graph at that instant.

Rate Law, Rate Constant and the Difference Between Order and Molecularity

The rate law expresses rate as rate = k[A]^x[B]^y , where the exponents are experimental, not stoichiometric. Their sum is the order of the reaction. The rate constant k carries units that depend on the order: mol L^-1s^-1 for zero order, s^-1 for first order, mol^-1L s^-1 for second order.

Order is experimental and can be zero, fractional or negative. Molecularity is the count of molecules colliding in an elementary step, always a positive integer. Order applies to overall or elementary reactions; molecularity only to elementary steps.

Integrated Rate Equation for Zero Order Reactions

For a zero order reaction A → products with rate = k , integration gives [A] = [A]₀ - kt . The concentration falls linearly with time and the half-life is t_1/2 = [A]₀2k , directly proportional to the initial concentration. Decomposition of HI on a gold surface and photochemical reactions are classic textbook examples.

Integrated Rate Equation for First Order Reactions and Half-Life

For a first order reaction with rate = k[A] , integration gives k = 2.303tlog[A]₀[A] . A plot of log[A] versus t is a straight line with slope -k/2.303 . The half-life is t_1/2 = 0.693k , independent of initial concentration, the signature of first order kinetics. Radioactive decay, decomposition of N₂O₅ and inversion of cane sugar are the standard examples.

Arrhenius Equation, Activation Energy and Collision Theory

The Arrhenius equation, k = A e^{-E_a / RT} , captures temperature dependence. Taking the log, a plot of ln k versus 1/T is linear with slope -E_a/R . For two temperatures, logk₂k₁ = E_a2.303 R[T₂ - T₁T₁ T₂] , the form CBSE numericals use. A 10 K rise near room temperature roughly doubles the rate, the temperature coefficient. Collision theory frames the same idea molecularly: rate = collision frequency × steric factor × e^-E_a/RT . Effective collisions are both energetic and properly oriented.

Chemical Kinetics Important Derivations for Class 12 Boards

Four derivations have appeared repeatedly on CBSE and JEE Main. The list below states what each one proves and the years it surfaced, so revision time goes to the highest-yield set.

How will Collegedunia's Notes Help You with Chemical Kinetics?

These notes are written by experts who have decoded the last five years of CBSE marking schemes for Class 12 Chemistry, so what you read here is what scores on the answer sheet.

• 2026-27 NCERT Alignment: Every concept matches the current 2026-27 syllabus, including the order of rate-law and Arrhenius sections in the new print.
• Graphs and Derivations: Concentration vs time graphs for zero and first order, plus the two-point Arrhenius derivation, are explained step by step in CBSE-style script.
• Expert Verification: Subject experts have re-checked every formula, unit, and graph against the latest NCERT textbook print.
• Last-Day Revision Anchors: Each topic ends with the one formula or graph CBSE markers most often reward, marked in yellow for quick recall.

Chemical Kinetics Class 12: Glossary of Must-Know Terms

These eight terms appear in CBSE one-mark MCQs and assertion-reason questions almost every year. Lock in the one-line definition for each before attempting the PYQ set.

Topics Covered in Class 12 Chemistry Chapter 3 Chemical Kinetics Notes

The notes resolve every high-search-volume sub-topic students ask Google before the board paper. Use the list as a checklist for the final revision pass.

• Rate of reaction class 12: average vs instantaneous rate, expression from stoichiometry, units mol L^-1 s^-1.
• Order of reaction vs molecularity: experimental vs theoretical, fractional vs whole-number, when each applies.
• First order reaction half life formula: derivation of t_1/2 = 0.693/k and the independence from [A]₀ .
• Second order reaction integrated rate law: 1/[A] - 1/[A]₀ = kt with unit check L mol^-1 s^-1.
• Arrhenius equation derivation: CBSE-style derivation from k = A e^-E_a/RT to the two-temperature log form.
• Activation energy graph: potential-energy profile, threshold energy, catalyst overlay.
• Pseudo first order reaction: ester hydrolysis, inversion of cane sugar; k' = k[H₂O] .
• Ester hydrolysis rate: acid-catalysed methyl acetate kinetics, NCERT Section 3.4 in full.
• k vs T plot: exponential rise of k with temperature; rate-doubling per 10 K rise.
• Rate constant units (zero, first, second order): general formula mol^1-n L^n-1 s^-1 with worked unit tables.
• Collision theory class 12: rate = P · Z_AB · e^-E_a/RT ; steric and energy factors.
• Temperature coefficient rate: k_T+10/k_T ≈ 2 to 3 as the empirical rate-doubling rule.
• Catalyst effect on E_a: lowers activation energy without altering Δ H or K_eq .
• Graph of ln k vs 1/T: slope -E_a/R of the Arrhenius line; the JEE Main MCQ trap.
• Arrhenius plot slope: the negative sign and the ₁₀ variant with slope -E_a/(2.303 R) .
• Half life formulas table: zero, first, and second-order half-lives compared side by side.

Chemical Kinetics Top 6 Formulae for Quick Recall

The six lines below are the formulae you will use most often in CBSE and JEE Main numericals on this chapter. The complete master sheet with dimensional checks and a when-to-use decision tree sits on the dedicated Collegedunia Formula Sheet for this chapter.

Full master table: Chemical Kinetics Class 12 Chemistry Formula Sheet

Frequently Asked Chemical Kinetics Questions in CBSE Board Exams (2021 to 2026)

The three patterns below recur almost every year in CBSE Class 12 Chemistry. Practise the technique behind each, not just the surface numbers.

Ques. A first order reaction takes 40 minutes for 30% decomposition. Calculate t_1/2 (CBSE 2023, 2025)

[3-Mark Question] Use k = 2.303tlog10070 to get k = 8.918 × 10^-3 min^-1 . Then t_1/2 = 0.693/k ≈ 77.7 minutes.

Ques. The rate constant of a reaction doubles when the temperature rises from 300 K to 310 K. Calculate E_a (CBSE 2021, JEE Main 2025)

[3-Mark Question] Use log 2 = E_a2.303 × 8.314[10300 × 310] . Solving gives E_a ≈ 53.6 kJ mol^-1 .

Ques. For a zero order reaction, derive the integrated rate law and show that t_1/2 ∝ [A]₀ (CBSE 2023, 2024)

[3-Mark Question] Start from -d[A]/dt = k , integrate from [A]₀ to [A] and 0 to t to get [A] = [A]₀ - kt . Setting [A] = [A]₀/2 gives t_1/2 = [A]₀/(2k) .

Class 12 Chemistry Chapter 3 Previous Year Questions Snapshot

A quick year-wise scan of where Chemical Kinetics surfaced across CBSE, JEE Main and NEET in the last six cycles. The fuller year-wise question map with topic tagging lives on the NCERT Solutions page for this chapter.

Full year-wise PYQ map: Chemical Kinetics Class 12 Chemistry NCERT Solutions

Common Misconceptions Students Hold in 12th Chemistry Chapter 3

These four wrong-beliefs are responsible for most of the dropped marks on this chapter. Address them before the board paper and the chapter becomes a steady scorer.

• Treating order and molecularity as the same thing. They agree only for single-step elementary reactions. A clear 1-mark loss in every cycle since 2022.
• Believing rate constant depends on concentration. The rate constant depends on temperature and the catalyst, not on reactant concentration. Rate depends on concentration; k does not.
• Reading half-life as half the total time. Half-life is the time for the concentration to fall to half its initial value, and for a first order reaction it stays constant through every successive half-life.
• Forgetting to convert ln to log when using 2.303 . The CBSE-friendly form of the first order law uses ₁₀ , so the factor of 2.303 must be retained.

Chemical Kinetics Weightage Compared Across Class 12 Chemistry Chapters

The visual below maps the typical CBSE marks distribution across all 10 chapters of the Class 12 Chemistry NCERT, averaged over the last five board papers. Chemical Kinetics shares the top band with Solutions, Coordination Compounds and Aldehydes-Ketones-Carboxylic Acids.

Related Links:

• Chemical Kinetics Class 12 Chemistry Handwritten Notes
• Chemical Kinetics Class 12 Chemistry Exemplar Solutions
• CBSE Class 12 Chemistry Sample Papers 2026

More Chemical Kinetics Chemistry Class 12 Resources

NCERT Notes for Class 12 Chemistry: All Chapters

Cycle through any of the other nine chapters of the Class 12 Chemistry NCERT below. Each link opens the chapter's full revision notes page.