Complete Summary and Solutions for Chemical Kinetics – NCERT Class XII Chemistry Part I, Chapter 3 – Rate of Reaction, Factors Affecting Rate, Order and Molecularity, Rate Law, Integrated Rate Equations, Collision Theory
Detailed summary and explanation of Chapter 3 'Chemical Kinetics' from the NCERT Class XII Chemistry Part I textbook, covering the concept of reaction rate, factors affecting rate of reaction, rate law and rate constant, order and molecularity of reactions, integrated rate equations for zero, first, and second order reactions, concept of activation energy and collision theory with examples, along with solved exercises and all NCERT questions and answers.
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Categories: NCERT, Class XII, Chemistry Part I, Chapter 3, Chemical Kinetics, Rate of Reaction, Rate Law, Collision Theory, Summary, Questions, Answers
Tags: Chemical Kinetics, Rate of Reaction, Order of Reaction, Molecularity, Rate Constant, Integrated Rate Law, Activation Energy, Collision Theory, NCERT, Class 12, Chemistry, Summary, Explanation, Questions, Answers, Chapter 3
Chemical Kinetics - Class 12 Chemistry Chapter 3 Ultimate Study Guide 2025
Chemical Kinetics
Chapter 3: Chemistry - Ultimate Study Guide | NCERT Class 12 Notes, Questions, Derivations & Quiz 2025
Full Chapter Summary & Detailed Notes - Chemical Kinetics Class 12 NCERT
Overview & Key Concepts
Chapter Goal: Understand reaction rates, mechanisms; thermodynamics vs. kinetics; factors like concentration, temp, catalyst. Exam Focus: Rate laws, order, integrated equations; 2025 Updates: Real-life apps (e.g., food spoilage, dental materials). Fun Fact: Diamond to graphite slow. Core Idea: Kinetics studies speed, not just feasibility. Real-World: Fuel burn in engines. Expanded: All subtopics point-wise with evidence (e.g., Table 3.1 rates), examples (e.g., butyl chloride), debates (e.g., average vs. instantaneous).
Wider Scope: From macroscopic (rates) to molecular (collisions); sources: Text, figures (3.1-3.2), examples.
Expanded Content: Include calculations, graphs; links (e.g., equilibrium); point-wise breakdown.
Introduction to Chemical Kinetics
Definition: Study of reaction rates, mechanisms; from Greek 'kinesis' (movement).
Tip: Group by type (rates/laws/orders); examples for recall. Depth: Debates (e.g., order vs. molecularity). Errors: Confuse average/instant. Interlinks: To equilibrium (Ch4). Advanced: Integrated laws. Real-Life: Drug decay. Graphs: Conc-time. Coherent: Evidence → Interpretation. For easy learning: Flashcard per term with formula.
60+ Questions & Answers - NCERT Based (Class 12) - From Exercises & Variations
Based on chapter + expansions. Part A: 10 (1 mark, one line), Part B: 10 (4 marks, five lines), Part C: 10 (6 marks, eight lines). Answers point-wise in black text.
Part A: 1 Mark Questions (10 Qs - Short)
1. Define chemical kinetics.
1 Mark Answer:
Study of reaction rates and mechanisms.
2. What is average rate?
1 Mark Answer:
Change in concentration over time interval.
3. Define instantaneous rate.
1 Mark Answer:
Rate at specific time (d[ ]/dt).
4. What is rate law?
1 Mark Answer:
Rate = k[reactants]^orders.
5. Define order of reaction.
1 Mark Answer:
Sum of exponents in rate law.
6. What is rate constant?
1 Mark Answer:
k in rate law.
7. Units of rate?
1 Mark Answer:
mol L⁻¹ s⁻¹.
8. Factor affecting rate?
1 Mark Answer:
Concentration.
9. What is zero order?
1 Mark Answer:
Rate independent of conc.
10. Elementary reaction?
1 Mark Answer:
Single step.
Part B: 4 Marks Questions (10 Qs - Medium, Exactly 5 Lines Each)
1. Explain average rate.
4 Marks Answer:
Δ[R]/Δt for reactant decrease.
Δ[P]/Δt for product increase.
Negative for reactants.
Ex: Butyl chloride hydrolysis.
Over interval, not instant.
2. Differentiate average/instantaneous rate.
4 Marks Answer:
Average: Over time Δt.
Instant: Limit Δt→0, d/dt.
Average constant interval.
Instant from tangent.
Ex: Fig 3.1 curves.
3. Describe rate expression.
4 Marks Answer:
Rate = k[A]^x [B]^y.
x,y experimental orders.
Not from stoichiometry.
Ex: NO+O2 rate k[NO]^2[O2].
Differential form dR/dt.
4. What is order?
4 Marks Answer:
Sum powers rate law.
0,1,2,fraction.
Zero: independent conc.
Ex: CHCl3+Cl2 half Cl2.
Experimental only.
5. Trends in rates.
4 Marks Answer:
Decreases as reactants deplete.
Increases with conc.
Table 3.1 shows fall.
Instant lower late.
Ex: Hydrolysis data.
6. Stoich coefficients in rate.
4 Marks Answer:
Divide by coeff for equal rate.
Ex: 2HI → H2+I2, rate -Δ[HI]/2Δt.
For products +Δ/coeff Δt.
Ex: Br- + BrO3- +6H+.
Gas: partial pressure.
7. Collision theory brief.
4 Marks Answer:
Molecules collide to react.
Effective with energy/orientation.
Explains rate factors.
Ex: Temp increases collisions.
Molecular level.
8. Positive catalyst effect.
4 Marks Answer:
Lowers activation energy.
Increases rate.
Not consumed.
Ex: Enzymes in body.
Alternate path.
9. Temperature dependence.
4 Marks Answer:
Increases rate.
More effective collisions.
Rate law includes.
Ex: Food spoils faster warm.
Arrhenius equation.
10. Elementary vs complex.
4 Marks Answer:
Elementary: One step, order=molecularity.
Complex: Multi-step, overall order.
Ex: Ionic fast elementary.
Mechanism sequence.
Rare single step.
Part C: 6 Marks Questions (10 Qs - Long, Exactly 8 Lines Each)
1. Discuss rate calculation.
6 Marks Answer:
Average: Δconc/Δt.
Instant: dconc/dt.
Negative reactants, positive products.
Adjust stoich coeffs.
Ex: R→P, rate -Δ[R]/Δt = Δ[P]/Δt.
Units mol L⁻¹ s⁻¹.
Graph: Slope tangent.
Gas: Pressure change.
2. Explain factors influencing rate.
6 Marks Answer:
Concentration: Rate law dependence.
Temperature: Increases collisions.
Catalyst: Lowers Ea.
Pressure: Gases if volume change.
Ex: Food spoil temp.
Molecular: Orientation/energy.
Control for applications.
Ex: Dental fast set.
3. Analyze rate law determination.
6 Marks Answer:
Experimental: Vary conc, measure rate.
Orders from ratios.
Not from equation.
Ex: NO+O2, double NO quadruples rate (order 2).
Table data analysis.
Fractional possible.
Differential equation.
Initial rates method.
4. Derive instantaneous rate.
6 Marks Answer:
Average r_av = Δ[R]/Δt.
As Δt→0, r_inst = d[R]/dt.
Graph: Tangent slope.
Ex: Butyl at 600s 5.12×10⁻⁵.
More accurate specific.
Limit process.
Negative d[R]/dt.
Positive d[P]/dt.
5. Discuss order examples.
6 Marks Answer:
Zero: Rate=k, independent.
First: Rate=k[A], ln[A] linear.
Second: k[A]^2 or [A][B].
Fractional: Ex CHCl3+Cl2 1/2 Cl2.
Ex: Ester hydrolysis pseudo-first.
Determine experimentally.
Molecularity for elementary.
Sum for overall.
6. Calculate butyl instant rate.
6 Marks Answer:
Plot conc vs time.
Tangent at t=600s.
Slope - (0.023/450) ≈5.12×10⁻⁵ mol L⁻¹ s⁻¹.
At 250s 1.22×10⁻⁴.
Decreases over time.
From Fig 3.2.
Graphical method.
Compare averages.
7. Why rates decrease?
6 Marks Answer:
Reactants deplete.
Less collisions.
Table 3.1 shows fall.
Instant lower late.
Ex: Hydrolysis 1.9 to 0.4×10⁻⁴.
Approach equilibrium.
Reverse starts.
Conc dependence.
8. Collision theory explain.
6 Marks Answer:
Molecules must collide.
Effective if energy >Ea, proper orientation.
Temp increases speed/fraction.
Conc more collisions.
Catalyst alternate low Ea path.
Ex: Gas reactions.
Molecular level.
Limitations complex.
9. Link to thermo.
6 Marks Answer:
Thermo: Feasibility ΔG<0.
Kinetics: Speed to equilibrium.
Ex: Diamond-graphite feasible but slow.
Extent from equilibrium.
Both needed understanding.
Rate alter conditions.
No direct predict rate from thermo.
Activation energy barrier.
10. Evaluate applications.
6 Marks Answer:
Design fast/slow materials.
Control industrial processes.
Understand spoilage/burning.
Enzymes biology.
Pharmacokinetics drugs.
Ex: Catalysts in cars.
Future: Green chemistry.
Predict time to completion.
Tip: Diagrams for rates; practice numericals. Additional 30 Qs: Variations on orders, rates.
Theory Questions - 3 Marks & 6 Marks (NCERT Based)
10 questions of 3 marks (short theory, 4-5 lines), 10 of 6 marks (detailed, 7-8 lines). Answers in black text.
3 Marks Questions (10 Qs)
1. Explain importance of kinetics.
3 Marks Answer:
Studies rate beyond feasibility.
Controls spoilage, fillings, engines.
Alters conditions for speed.
Macro to molecular level.
2. Define rate for R→P.
3 Marks Answer:
-Δ[R]/Δt or +Δ[P]/Δt.
Conc in mol L⁻¹, time s.
Negative reactant decrease.
Volume constant assumed.
3. Why negative sign in rate?
3 Marks Answer:
Reactant conc decreases.
Makes rate positive.
For products positive.
Convention for speed.
4. Units of rate.
3 Marks Answer:
mol L⁻¹ s⁻¹ solution.
atm s⁻¹ gas pressure.
Conc time⁻¹ general.
Ex: Butyl mol L⁻¹ s⁻¹.
5. Role of stoich in rate.
3 Marks Answer:
Divide Δ by coeff.
Ex: 2HI, -Δ[HI]/2Δt.
Equal overall rate.
Not for order.
6. What is rate law?
3 Marks Answer:
Experimental expression.
k[reactants]^powers.
Orders not stoich.
Ex: CH3COOC2H5 zero H2O.
7. Define order.
3 Marks Answer:
Sum exponents rate law.
0,1,2,fraction.
Ex: (a) 2, (b) 1/2.
Experimental.
8. Elementary reaction.
3 Marks Answer:
Single step.
Order = molecularity.
Ex: Ionic fast.
Rare complex.
9. Collision theory.
3 Marks Answer:
Collisions needed.
Effective with Ea, orientation.
Explains factors.
Molecular.
10. Catalyst effect.
3 Marks Answer:
Lowers Ea.
Increases rate.
Not consumed.
Alternate path.
6 Marks Questions (10 Qs)
1. Distinguish kinetics/thermo.
6 Marks Answer:
Kinetics: Rate, mechanism.
Thermo: Feasibility ΔG, extent equilibrium.
Ex: Diamond-graphite slow despite feasible.
Kinetics alters speed conditions.
Both complete understanding.
Thermo no predict rate.
Ex: Food spoil rate.
2. Explain instantaneous rate determination.
6 Marks Answer:
Plot conc vs time.
Draw tangent at t.
Slope = rate.
Ex: Butyl 600s 5.12×10⁻⁵.
Better than average for point.
As Δt→0 limit.
Graph Fig 3.2.
3. How determine order?
6 Marks Answer:
Vary one conc, others constant.
Rate ratio = (conc ratio)^order.
Ex: Double conc, quadruple rate order 2.
Initial rates table.
Not stoich.
Ex: NO+O2 order 2 NO, 1 O2.
Fractional possible.
4. Discuss complex reactions.
6 Marks Answer:
Multi elementary steps.
Overall rate from law.
Mechanism sequence.
Order not molecularity.
Ex: N2O5 decomposition.
Rare single step.
Rate determining slow step.
5. Temperature effect on rate.
6 Marks Answer:
Increases kinetic energy.
More collisions exceed Ea.
Rate doubles ~10°C rise.
Ex: Spoilage faster warm.
Arrhenius k=Ae^(-Ea/RT).
Collision theory basis.
Control reactions.
6. Catalyst in kinetics.
6 Marks Answer:
Lowers Ea alternate path.
Increases rate, not yield.
Not consumed.
Ex: Enzymes biological.
Positive catalyst speed up.
Negative slow down.
Industrial importance.
7. Order vs molecularity.
6 Marks Answer:
Order: Experimental sum powers.
Molecularity: Molecules per step.
Order fraction, molecularity integer.
Order overall, molecularity elementary.
Ex: Complex order not molecularity.
Order from data, molecularity mechanism.
Equal for elementary.
8. Collision theory details.
6 Marks Answer:
React on collision.
Need min energy Ea.
Proper orientation.
Rate ∝ collisions.
Temp increases fraction with Ea.
Conc increases number.
Limitations: Not all collide react.
9. Zero order characteristics.
6 Marks Answer:
Rate = k, constant.
Independent conc.
[A] = [A]0 - kt linear.
Ex: Enzyme saturated.
Units mol L⁻¹ s⁻¹.
t1/2 = [A]0/2k.
Rare but important.
10. First order characteristics.
6 Marks Answer:
Rate = k[A].
ln[A] = ln[A]0 - kt linear.
t1/2 = 0.693/k constant.
Ex: Radioactive decay.
Units s⁻¹.
Pseudo-first high other conc.
Common unimolecular.
Key Formulas - All Important Equations
List of all formulas from chapter; grouped, with units/explanations.
Formula
Description
Units/Example
r_av = -Δ[R]/Δt
Average rate reactant
mol L⁻¹ s⁻¹; butyl example
r_inst = -d[R]/dt
Instantaneous rate
mol L⁻¹ s⁻¹; tangent slope
Rate = k[A]^x [B]^y
Rate law
k units vary; NO^2 O2
Order = x + y
Total order
Dimensionless; 3 for example
Rate = -Δ[HI]/2Δt
Stoich adjustment
For 2HI→H2+I2
r = - (1/5)Δ[Br-]/Δt
Br- reaction example
Multi-reactant
k = rate / [conc]^order
Rate constant
Varies by order
[A] = [A]0 - kt
Zero order integrated
Linear plot
ln[A] = ln[A]0 - kt
First order integrated
ln plot linear
1/[A] = 1/[A]0 + kt
Second order integrated
1/[A] linear
Tip: Memorize with orders; practice units change.
Derivations - Detailed Guide
Key derivations with steps; from PDF (e.g., instantaneous, rate law).
