Chemical Kinetics: Complete Guide & Formula Sheet with Free PDF Download (JEE & NEET)
Chemical Kinetics — Competishun
Chemical Kinetics: Complete Guide & Formula Sheet with Free PDF Download (JEE & NEET)
Chemical Kinetics is one of the most scoring and conceptually rich chapters in physical chemistry. It carries high weightage in JEE and NEET, with 2-3 questions appearing every year.
This chapter deals with the speed of chemical reactions, the factors that affect reaction rates, and the mechanisms by which reactions proceed. It covers rate laws, order and molecularity of reactions, integrated rate equations, half-life, and the Arrhenius equation.
This page gives you the complete guide to Chemical Kinetics with all concepts explained in depth. You will find clear definitions, derivations, worked examples, and common mistakes to avoid. Download the free PDF below and keep it handy for quick revision before your JEE Main, JEE Advanced, or NEET exam.
Download the Chemical Kinetics Complete Guide PDF
Get all Chemical Kinetics concepts, formulas, and derivations in one clean PDF, free. Perfect for JEE and NEET revision.
Download Free PDFWhat is Chemical Kinetics?
Chemical Kinetics is divided into two main areas of study:
Rate of Reaction
How fast a reaction occurs. Measured as the change in concentration of reactants or products per unit time.
Reaction Mechanism
The step-by-step sequence of elementary reactions by which a chemical change occurs.
Rate of Reaction
Average Rate vs Instantaneous Rate
| Type | Definition | Formula |
|---|---|---|
| Average Rate | Rate over a time interval | ravg = -Δ[R]/Δt = +Δ[P]/Δt |
| Instantaneous Rate | Rate at a specific instant | rinst = -d[R]/dt = +d[P]/dt |
| The instantaneous rate is the slope of the tangent to the concentration-time graph at that point. | ||
Factors Affecting Rate of Reaction
- Concentration: Higher concentration generally leads to a higher rate due to more frequent collisions.
- Temperature: Increasing temperature increases the rate because more molecules have energy greater than the activation energy.
- Catalyst: A catalyst provides an alternative pathway with lower activation energy, increasing the rate without being consumed.
- Surface Area: For heterogeneous reactions, a larger surface area increases the rate.
- Nature of Reactants: Ionic reactions are generally faster than covalent reactions.
Rate Law and Order of Reaction
| Concept | Definition | Example |
|---|---|---|
| Rate Law | r = k[A]m[B]n | For reaction 2NO + O₂ → 2NO₂, r = k[NO]²[O₂] |
| Order of Reaction | m + n (sum of exponents) | For the above, order = 2 + 1 = 3 (third order) |
| Molecularity | Number of molecules participating in the rate-determining step | Always a whole number (1, 2, or 3) |
| Rate Constant (k) | Proportionality constant in the rate law | Depends on temperature and catalyst |
| Order is determined experimentally; molecularity is derived from the reaction mechanism. | ||
Units of Rate Constant (k)
| Order | Units of k |
|---|---|
| Zero Order | mol L⁻¹ s⁻¹ |
| First Order | s⁻¹ |
| Second Order | L mol⁻¹ s⁻¹ |
| nth Order | (mol L⁻¹)1-n s⁻¹ |
| The units of k depend on the overall order of the reaction. Memorize these for JEE and NEET. | |
Integrated Rate Equations
Integrated rate equations relate the concentration of reactants to time. They are essential for solving kinetics problems in JEE and NEET.
| Order | Integrated Rate Equation | Straight Line Plot | Half-Life |
|---|---|---|---|
| Zero Order | [A] = [A]₀ - kt | [A] vs t | t½ = [A]₀ / 2k |
| First Order | ln[A] = ln[A]₀ - kt | ln[A] vs t | t½ = 0.693 / k |
| Second Order | 1/[A] = 1/[A]₀ + kt | 1/[A] vs t | t½ = 1 / k[A]₀ |
| The half-life of a first-order reaction is independent of the initial concentration. This is a key feature of first-order reactions. | |||
First-Order Reactions — Special Case
For a first-order reaction, the integrated rate equation can also be written as:
This form is often used in numerical problems.
Half-Life of a Reaction
| Order | Half-Life Formula | Dependence on [A]₀ |
|---|---|---|
| Zero Order | t½ = [A]₀ / 2k | Proportional to [A]₀ |
| First Order | t½ = 0.693 / k | Independent of [A]₀ |
| Second Order | t½ = 1 / k[A]₀ | Inversely proportional to [A]₀ |
| nth Order | t½ ∝ 1 / [A]₀n-1 | Depends on [A]₀ |
| The half-life of a first-order reaction is constant and does not depend on the initial concentration. This is a unique feature of first-order reactions. | ||
Arrhenius Equation — Temperature Dependence of Rate
| Form | Equation |
|---|---|
| Exponential Form | k = A e-Ea/RT |
| Logarithmic Form | ln k = ln A - Ea/RT |
| Two-Temperature Form | ln(k₂/k₁) = (Ea/R)(1/T₁ - 1/T₂) |
| Where: k = rate constant, A = frequency factor, Ea = activation energy, R = gas constant, T = temperature. | |
Activation Energy (Ea)
Activation energy is the minimum energy that reactant molecules must possess to undergo a reaction. It is the energy barrier that must be overcome for a reaction to occur.
- Higher Ea: Slower reaction, stronger temperature dependence
- Lower Ea: Faster reaction, weaker temperature dependence
- Catalyst: Lowers Ea by providing an alternative pathway
This is the most frequently used form of the Arrhenius equation in JEE and NEET numerical problems.
Reaction Mechanism and Molecularity
Types of Molecularity
| Type | Number of Molecules | Example |
|---|---|---|
| Unimolecular | 1 | A → Products |
| Bimolecular | 2 | A + B → Products |
| Termolecular | 3 | 2A + B → Products |
| Molecularity is always a whole number (1, 2, or 3). Termolecular reactions are rare. | ||
Order vs Molecularity
| Feature | Order | Molecularity |
|---|---|---|
| Definition | Sum of powers in rate law | Number of molecules in elementary step |
| Determination | Experimentally determined | Theoretically from mechanism |
| Values | Can be zero, fractional, or integer | Always a whole number |
| Applicability | Applies to overall reaction | Applies to elementary steps |
| For elementary reactions, order equals molecularity. For complex reactions, order is determined by the slowest step (rate-determining step). | ||
All Chemical Kinetics Formulas at a Glance
| Formula | What It Means |
|---|---|
| Rate = -d[R]/dt = +d[P]/dt | Rate of reaction |
| r = k[A]m[B]n | Rate law |
| [A] = [A]₀ - kt | Zero-order integrated rate equation |
| ln[A] = ln[A]₀ - kt | First-order integrated rate equation |
| 1/[A] = 1/[A]₀ + kt | Second-order integrated rate equation |
| t½ = 0.693 / k | Half-life for first-order |
| k = A e-Ea/RT | Arrhenius equation |
| ln(k₂/k₁) = (Ea/R)(1/T₁ - 1/T₂) | Two-temperature Arrhenius equation |
| Memorise these formulas for Chemical Kinetics. They are the key to scoring full marks in this chapter. | |
Common Mistakes in Chemical Kinetics
- Confusing order and molecularity: Order is experimental, molecularity is theoretical. For complex reactions, they are not the same.
- Forgetting the units of k: The units of k depend on the overall order of the reaction. This is a common source of errors.
- Misapplying the half-life formula: t½ = 0.693/k is only for first-order reactions. For other orders, the formula is different.
- Using the wrong form of the Arrhenius equation: Make sure you use the correct form depending on whether you have one temperature or two.
- Forgetting that the rate of a reaction depends on the concentration of reactants, not products: This is a fundamental principle in Chemical Kinetics.
Why Chemical Kinetics Matters for JEE and NEET
- High weightage: Chemical Kinetics appears in 2-3 questions in every JEE Main, JEE Advanced, and NEET chemistry paper.
- Foundation for physical chemistry: Understanding Chemical Kinetics helps you with thermodynamics, equilibrium, and electrochemistry.
- Direct scoring: Many questions are direct formula-based, especially rate laws, integrated equations, and the Arrhenius equation.
- Real-world applications: Chemical Kinetics connects to drug metabolism, enzyme kinetics, catalysis, and environmental chemistry.
- Conceptual clarity: This chapter rewards students who understand the concepts rather than just memorizing formulas.
Get the Complete Chemical Kinetics PDF for Free
Download the full Chemical Kinetics guide with all concepts, definitions, formulas, and derivations. Perfect for last-minute revision before JEE and NEET.
Download Free PDFMaster Chemistry with Competishun
Competishun teaches complete JEE and NEET chemistry with structured lectures, DPPs, PYQs and an All India Test Series.
All taught by faculty with 18 to 25 years of experience.
Pratham
Two-year foundation program that builds strong Class 11 chemistry, physics and maths concepts.
Explore PrathamPrakhar
Class 12 program balancing boards, JEE Main and Advanced preparation together.
Explore PrakharPraveen & Fast Lane
Dropper program for a focused repeat attempt, including the accelerated Fast Lane batch.
Explore PraveenPragyaan
Live interactive batch with real-time classes and mentorship for JEE and NEET.
Explore PragyaanDLP Study Material
Complete printed material with DPPs and PYQs for Class 11, Class 12 and droppers, delivered home.
Explore DLPAll India Test Series
Regular JEE and NEET level tests with detailed analysis to track and improve your rank.
Explore Test SeriesFree Chemistry Lectures on YouTube
Want to see Chemical Kinetics taught step by step with real problem-solving? Competishun's full concept lectures are free on its YouTube channel.
More than 2.2 million+ students follow the channel for free concept lectures, PYQ solutions and exam strategy.
Learn the concepts, then use this Chemical Kinetics guide to revise.
Build Your Chemistry Foundation
Class 11, Class 12 or dropper, explore every Competishun program.
Or start free with full concept lectures on YouTube.
About Competishun
Competishun is an online JEE and NEET coaching platform with programs for Class 11, Class 12 and droppers.
Complete DLP study material and an All India Test Series covering JEE Main, Advanced and NEET.
Taught by faculty with 18 to 25 years of experience.
More than 2.2 million+ students follow the Competishun YouTube channel.
Free JEE and NEET Concept Lectures
Follow Competishun for free Physics, Chemistry and Biology lectures, PYQ solutions and strategy.
Read These Next
Galvanic cells, Nernst equation, conductance, Kohlrausch law, Faraday's laws and batteries explained in depth.
Acids, bases, pH, hydrolysis, buffers and solubility product explained in depth.
First law, enthalpy, entropy, Gibbs free energy and Hess's law with examples.
Frequently Asked Questions — Chemical Kinetics
Tags
