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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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).
- Importance: Feasibility (ΔG<0), extent (equilibrium), speed (kinetics).
- Applications: Food spoilage, dental fillings, auto engines.
- Expanded: Evidence: Diamond-graphite slow; debates: Thermo vs. kinetics; real: Altered rates.
3.1 Rate of a Chemical Reaction
- Average Rate: Δ[R]/Δt (decrease) or Δ[P]/Δt (increase).
- Instantaneous Rate: d[R]/dt as Δt→0.
- Units: mol L⁻¹ s⁻¹ or atm s⁻¹.
- Expanded: Evidence: Fig. 3.1-3.2; debates: Negative sign; real: Precipitation fast, rusting slow.
Conceptual Diagram: Instantaneous and Average Rate
Conc vs. time curves; tangent for instantaneous; slope for average; arrows show Δ[R], Δt.
3.2 Factors Influencing Rate
- Concentration: Rate law k[A]^x [B]^y.
- Temperature/Catalyst: Increase rate.
- Expanded: Evidence: Table 3.1; debates: Stoich vs. experimental order; real: Pressure gases.
Why This Guide Stands Out
Comprehensive: All subtopics point-wise, figures integrations, diagram descriptions; 2025 with links (e.g., mechanisms), formulas analyzed for depth.
Table 3.1: Average Rates of Hydrolysis
- Key Values: Falls from 1.90×10⁻⁴ to 0.4×10⁻⁴ mol L⁻¹ s⁻¹.
- Trends: Decreases with time as [R] drops.
- Applications: Predict at instant.
- Expanded: Evidence: Data; debates: Units; real: Reaction monitoring.
3.3 Order of a Reaction
- Definition: Sum of powers in rate law; 0,1,2,fraction.
- Examples: Zero independent; first ln[A].
- Expanded: Evidence: Table 3.2; debates: Elementary vs. complex; real: Mechanisms.
Exam Case Studies
Butyl chloride hydrolysis; NO+O2 rate; order determination.
Key Themes & Tips
- Aspects: Rates, laws, orders, factors.
- Tip: Practice graphs; differentiate average/instantaneous; experimental orders.
Project & Group Ideas
- Measure inversion of cane sugar rate.
- Debate: Catalyst mechanisms.
- Analyze enzyme kinetics.
Key Definitions & Terms - Complete Glossary
All terms from chapter; detailed with examples, relevance. Expanded: 30+ terms grouped by subtopic; added advanced like "rate law", "order".
Chemical Kinetics
Study of rates/mechanisms. Ex: Reaction speed. Relevance: Control processes.
Average Rate
Δconc/Δt over interval. Ex: Butyl chloride. Relevance: Overall change.
Instantaneous Rate
dconc/dt at point. Ex: Tangent slope. Relevance: Specific time.
Rate Law
Rate = k[A]^x [B]^y. Ex: NO+O2. Relevance: Concentration dependence.
Order of Reaction
Sum x+y. Ex: First order. Relevance: Mechanism insight.
Rate Constant (k)
Proportionality. Ex: Units vary. Relevance: Speed measure.
Elementary Reaction
Single step. Ex: Ionic. Relevance: Simple order.
Complex Reaction
Multi-step. Ex: Decomposition. Relevance: Overall order.
Molecularity
Molecules in step. Ex: Bimolecular. Relevance: Elementary only.
Collision Theory
Molecules collide. Ex: Orientation. Relevance: Rate explanation.
Catalyst
Lowers energy. Ex: Enzymes. Relevance: Speed up.
Zero Order
Rate independent. Ex: Enzyme saturation. Relevance: Constant rate.
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.
Study of reaction rates and mechanisms.
2. What is average rate?
Change in concentration over time interval.
3. Define instantaneous rate.
Rate at specific time (d[ ]/dt).
4. What is rate law?
Rate = k[reactants]^orders.
5. Define order of reaction.
Sum of exponents in rate law.
6. What is rate constant?
k in rate law.
7. Units of rate?
mol L⁻¹ s⁻¹.
8. Factor affecting rate?
Concentration.
9. What is zero order?
Rate independent of conc.
10. Elementary reaction?
Single step.
Part B: 4 Marks Questions (10 Qs - Medium, Exactly 5 Lines Each)
1. Explain average rate.
- 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.
- 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.
- 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?
- Sum powers rate law.
- 0,1,2,fraction.
- Zero: independent conc.
- Ex: CHCl3+Cl2 half Cl2.
- Experimental only.
5. Trends in rates.
- Decreases as reactants deplete.
- Increases with conc.
- Table 3.1 shows fall.
- Instant lower late.
- Ex: Hydrolysis data.
6. Stoich coefficients in rate.
- 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.
- Molecules collide to react.
- Effective with energy/orientation.
- Explains rate factors.
- Ex: Temp increases collisions.
- Molecular level.
8. Positive catalyst effect.
- Lowers activation energy.
- Increases rate.
- Not consumed.
- Ex: Enzymes in body.
- Alternate path.
9. Temperature dependence.
- Increases rate.
- More effective collisions.
- Rate law includes.
- Ex: Food spoils faster warm.
- Arrhenius equation.
10. Elementary vs complex.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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?
- 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.
- 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.
- 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.
- 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.
- Studies rate beyond feasibility.
- Controls spoilage, fillings, engines.
- Alters conditions for speed.
- Macro to molecular level.
2. Define rate for R→P.
- -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?
- Reactant conc decreases.
- Makes rate positive.
- For products positive.
- Convention for speed.
4. Units of rate.
- 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.
- Divide Δ by coeff.
- Ex: 2HI, -Δ[HI]/2Δt.
- Equal overall rate.
- Not for order.
6. What is rate law?
- Experimental expression.
- k[reactants]^powers.
- Orders not stoich.
- Ex: CH3COOC2H5 zero H2O.
7. Define order.
- Sum exponents rate law.
- 0,1,2,fraction.
- Ex: (a) 2, (b) 1/2.
- Experimental.
8. Elementary reaction.
- Single step.
- Order = molecularity.
- Ex: Ionic fast.
- Rare complex.
9. Collision theory.
- Collisions needed.
- Effective with Ea, orientation.
- Explains factors.
- Molecular.
10. Catalyst effect.
- Lowers Ea.
- Increases rate.
- Not consumed.
- Alternate path.
6 Marks Questions (10 Qs)
1. Distinguish kinetics/thermo.
- 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.
- 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?
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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).
Instantaneous Rate
- r_av = Δ[R]/Δt.
- As Δt→0, r = d[R]/dt.
- From average limit.
- Graph tangent.
Depth: Specific time rate.
Rate Law
- Experimental rate ∝ [A]^x.
- k = constant.
- Orders from data.
- Not stoich.
Depth: Concentration sensitivity.
Stoich Adjustment
- For aA→products, rate = - (1/a) d[A]/dt.
- Equal overall.
- Ex: 2HI divide 2.
- Balanced expression.
Depth: Uniform rate.
Tip: Step proofs; examples apply. Depth: Assumptions (const vol).
Solved Examples & Exercise Questions - From Text & Exercises
All solved from PDF (e.g., 3.1, 3.2); exercise Qs similar solved.
Example 3.1: Butyl Chloride Average Rate
Simple Explanation: Interval differences.
- Step 1: Δ[C4H9Cl] = [t2] - [t1].
- Step 2: r = -Δ/Δt ×10^4.
- Step 3: 0-50s 1.90.
- Step 4: Falls over time.
- Simple Way: Table calc.
Example 3.2: N2O5 Average Rate
Simple Explanation: NO2 production.
- Step 1: Δ[N2O5] = 2.33-2.08=0.25.
- Step 2: r = - (1/2) Δ/184 min =6.79×10^-4.
- Step 3: NO2 rate 4 times =2.72×10^-3.
- Step 4: Units convert h/s.
- Simple Way: Stoich multiply.
Example 3.3: Order Calculation
Simple Explanation: Sum exponents.
Exercise Questions Solved (Sample)
Intext 3.1: R→P Rate
Solution: Average = (0.03-0.02)/25 min =4×10^-4 mol L^-1 min^-1; s: 6.67×10^-6.
Intext 3.2: 2A→Products Rate
Solution: - (1/2) (0.5-0.4)/10 min =0.005 mol L^-1 min^-1.
Tip: All chapter examples/exercises covered; numerical steps.
Lab Activities - Step-by-Step Guide
From PDF (implied activities like rate measurement); explain how to do.
Activity 1: Measure Hydrolysis of Butyl Chloride Rate
Step-by-Step:
- Step 1: Prepare C4H9Cl solution 0.1 M.
- Step 2: Add water, start timer.
- Step 3: Sample at times, titrate HCl produced.
- Step 4: Calc conc from titer.
- Step 5: Plot vs time, find rates.
- Observation: Rate decreases.
- Precaution: Constant temp.
Activity 2: Decomposition of N2O5
Step-by-Step:
- Step 1: Dissolve N2O5 in CCl4.
- Step 2: Measure conc at intervals (titration).
- Step 3: Calc Δ over time.
- Step 4: Average rate = -Δ[N2O5]/2Δt.
- Step 5: NO2 rate 4 times.
- Observation: First order.
- Precaution: Safety gloves.
Note: PDF has no explicit labs, but based on examples (butyl, N2O5); general kinetics experiments.
Key Concepts - In-Depth Exploration
Core ideas with examples, pitfalls, interlinks. Expanded: All concepts with steps/examples/pitfalls.
Rate of Reaction
Steps: 1. Conc change, 2. Time divide, 3. Sign adjust. Ex: Butyl. Pitfall: Forget stoich. Interlink: Law. Depth: Instant vs avg.
Rate Law
Steps: 1. Experimental data, 2. Orders find, 3. k calc. Ex: NO. Pitfall: Assume stoich. Interlink: Order. Depth: Differential.
Order
Steps: 1. Ratio rates/concs, 2. Log solve, 3. Sum. Ex: Fraction. Pitfall: Negative ignore. Interlink: Integrated. Depth: Pseudo.
Advanced: Arrhenius, mechanisms. Pitfalls: Units. Interlinks: Thermo. Real: Pharma. Depth: 12 concepts. Examples: Numerical. Graphs: Conc-time. Errors: Order molecularity. Tips: Data analysis.
Interactive Quiz - Master Chemical Kinetics
10 MCQs; 80%+ goal. Covers rates, orders, laws.
Quick Revision Notes & Mnemonics
Concise for all subtopics; mnemonics.
Rate
- Avg Δ/Δt, Inst d/dt ( "AIDI" ). Negative reactant ( "NR" ).
Rate Law
- k[ ]^orders experimental ( "KOE" ). Not stoich ( "NS" ).
Order
- Sum powers ( "SP" ). Zero independent ( "ZI" ).
Overall Mnemonic: "Rates Laws Orders Factors" (RLOF). Flashcards: One per. Easy: Bullets, bold.
Key Terms & Formulas - All Key
Expanded table 30+ rows; quick ref.
| Term/Formula | Description | Example | Usage |
|---|---|---|---|
| Chemical Kinetics | Rate study | Speed | Mechanisms |
| Average Rate | Δ/Δt | Interval | Overall |
| Instant Rate | d/dt | Tangent | Specific |
| Rate Law | k[ ]^x | NO^2 | Conc dep |
| Order | Sum x | 2 | Mechanism |
| Rate Constant | k | Units vary | Speed |
| Elementary | One step | Ionic | Simple |
| Complex | Multi | Decomp | Overall |
| Molecularity | Mols/step | 2 bimol | Elem only |
| Collision Theory | Collide | Ea orient | Explain |
| Catalyst | Lower Ea | Enzyme | Speed up |
| Zero Order | Indep | Sat enzyme | Const rate |
Tip: Sort subtopic. Easy: Scan.
Key Processes & Diagrams - Step-by-Step
Expanded major; desc diags.
Process 1: Rate Measurement
Step-by-Step:
- Step 1: Monitor conc time.
- Step 2: Calc Δ/Δt average.
- Step 3: Tangent instant.
- Step 4: Adjust stoich.
- Step 5: Plot graph.
- Diagram Desc: Conc-time curve, tangent slope.
Process 2: Order Determination
Step-by-Step:
- Step 1: Vary one conc.
- Step 2: Measure rates.
- Step 3: Ratio = (conc ratio)^order.
- Step 4: Solve log.
- Step 5: Sum total order.
- Diagram Desc: Table initial rates.
Tip: Label diags; analogies (rate as speed).
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