Chemical Kinetics and Surface Chemistry - NEET PYQs (2009-2024)

🎯 Overview

Welcome to the comprehensive collection of NEET Previous Year Questions on “Chemical Kinetics and Surface Chemistry” from 2009-2024. This important chapter consistently appears with 3-4 questions annually, covering reaction rates, rate laws, collision theory, catalysts, adsorption, colloids, and surface phenomena. The questions require both mathematical skills and conceptual understanding.

📊 Chapter Analysis & Statistics

Question Distribution

📈 PYQ Distribution (2009-2024):
- Total Questions: 40-50 questions
- Average per year: 3-4 questions
- Difficulty Level: Medium
- Success Rate: 55-70%
- Time per Question: 1-2 minutes

🎯 Weightage in NEET:
- 3-4 questions per year
- 12-16 marks per year
- 7-9% of Chemistry section
- 15-20% of Physical Chemistry

Topic-wise Distribution

📚 Topic Coverage:
1. Chemical Kinetics (Rate Laws, Order, Molecularity): 60% of questions
2. Surface Chemistry (Adsorption, Colloids): 40% of questions

🔍 Core Concepts and Formulas

1. Chemical Kinetics - Rate of Reaction

⚡ Rate of Reaction:
Rate = -d[Reactant]/dt = +d[Product]/dt

📊 Units of Rate:
- For concentration: mol·L⁻¹·s⁻¹
- For pressure: atm·s⁻¹ or Pa·s⁻¹

🔢 Rate Law Expression:
For reaction: aA + bB → Products
Rate = k[A]^m[B]^n

Where:
- k = Rate constant
- m, n = Orders with respect to A and B
- Overall order = m + n

2. Order and Molecularity

📊 Order of Reaction:
- Sum of powers of concentration terms in rate law
- Determined experimentally
- Can be zero, fractional, or integer

📊 Molecularity:
- Number of molecules colliding in elementary step
- Always a positive integer
- Theoretical concept

📊 Common Orders and Rate Laws:
Zero order: Rate = k
First order: Rate = k[A]
Second order: Rate = k[A]² or k[A][B]
Pseudo first order: Rate = k'[A] when [B] is constant

3. Integrated Rate Equations

📊 Zero Order Reaction:
Rate = k
[A]t = [A]₀ - kt
t₁/₂ = [A]₀/(2k)

📊 First Order Reaction:
Rate = k[A]
ln[A]t = ln[A]₀ - kt
log[A]t = log[A]₀ - (kt/2.303)
t₁/₂ = 0.693/k

📊 Second Order Reaction (single reactant):
Rate = k[A]²
1/[A]t = 1/[A]₀ + kt
t₁/₂ = 1/(k[A]₀)

4. Temperature Dependence

🌡️ Arrhenius Equation:
k = A × e^(-Ea/RT)

Where:
- k = Rate constant
- A = Pre-exponential factor (frequency factor)
- Ea = Activation energy
- R = Gas constant (8.314 J·K⁻¹·mol⁻¹)
- T = Temperature (Kelvin)

📊 Linear Form:
ln k = ln A - Ea/(RT)
log k = log A - Ea/(2.303RT)

📊 Temperature Coefficient:
k(T+10)/k(T) = temperature coefficient (usually 2-3)

5. Collision Theory

💥 Collision Theory Requirements:
1. Proper orientation of molecules
2. Sufficient kinetic energy (≥ Ea)
3. Effective collisions

📊 Rate Expression:
Rate = Z × e^(-Ea/RT) × p
Where:
- Z = Collision frequency
- e^(-Ea/RT) = Fraction of molecules with sufficient energy
- p = Orientation factor (steric factor)

6. Catalysts

🚀 Catalyst Effects:
- Provide alternative reaction pathway
- Lower activation energy
- Do not affect equilibrium position
- Speed up both forward and reverse reactions equally

📊 Catalysis Types:
1. Homogeneous: Catalyst and reactants in same phase
2. Heterogeneous: Catalyst and reactants in different phases
3. Enzyme: Biological catalysts

7. Adsorption

📊 Definition:
Accumulation of molecules on surface

🔬 Types of Adsorption:
1. Physical Adsorption (Physisorption):
   - Weak van der Waals forces
   - Low heat of adsorption (20-40 kJ/mol)
   - Reversible
   - Multi-layer formation
   - No specificity

2. Chemical Adsorption (Chemisorption):
   - Strong chemical bonds
   - High heat of adsorption (40-400 kJ/mol)
   - Irreversible
   - Mono-layer formation
   - Highly specific

📈 Adsorption Isotherms:
Freundlich: x/m = kP^(1/n)
Langmuir: x/m = (KP)/(1+KP)

8. Colloids

🧪 Colloidal System:
Dispersed phase (1-1000 nm) in dispersion medium

📊 Classification:
1. Based on physical state:
   - Sol: Solid in liquid
   - Gel: Liquid in solid
   - Emulsion: Liquid in liquid
   - Foam: Gas in liquid
   - Solid foam: Gas in solid

2. Based on nature:
   - Lyophilic (solvent-loving): Stable
   - Lyophobic (solvent-hating): Unstable

🔬 Properties of Colloids:
- Tyndall effect (light scattering)
- Brownian motion
- Electrophoresis (charged particles)
- Coagulation (destabilization)

9. Catalysis and Surface Chemistry

🏭 Heterogeneous Catalysis:
- Surface adsorption important
- Active sites on catalyst surface
- Langmuir-Hinshelwood mechanism
- Example: Haber process, Contact process

🧪 Enzyme Catalysis:
- Highly specific
- Optimum temperature and pH
- Lock and key mechanism
- Michaelis-Menten kinetics

📈 Year-wise Question Analysis

Recent NEET Questions (2019-2024)

2024 NEET Questions

📝 Question 1: First Order Reaction
A first order reaction is 50% complete in 40 minutes. Calculate the rate constant.

Solution:
For first order reaction:
t₁/₂ = 0.693/k
Given t₁/₂ = 40 minutes

k = 0.693/40 = 0.01733 min⁻¹

Answer: 0.01733 min⁻¹

📝 Question 2: Activation Energy
The rate constant doubles when temperature increases from 300 K to 310 K. Calculate activation energy.

Solution:
Using Arrhenius equation:
k₂/k₁ = e^[-Ea/R(1/T₂ - 1/T₁)]
Given k₂/k₁ = 2, T₁ = 300 K, T₂ = 310 K

2 = e^[-Ea/8.314(1/310 - 1/300)]
ln 2 = -Ea/8.314 × (0.003226 - 0.003333)
0.693 = -Ea/8.314 × (-0.000107)
0.693 = Ea × 0.000107/8.314
Ea = 0.693 × 8.314/0.000107 = 53866 J/mol = 53.9 kJ/mol

Answer: 53.9 kJ/mol

2023 NEET Questions

📝 Question 1: Order of Reaction
For the reaction: 2A + B → Products
The following data was obtained:
Experiment 1: [A] = 0.1 M, [B] = 0.1 M, Rate = 4.0 × 10⁻⁴
Experiment 2: [A] = 0.2 M, [B] = 0.1 M, Rate = 8.0 × 10⁻⁴
Experiment 3: [A] = 0.1 M, [B] = 0.2 M, Rate = 8.0 × 10⁻⁴

Find the order with respect to A and B.

Solution:
Compare Experiment 1 and 2 (B constant, A doubles):
Rate doubles (8.0/4.0 = 2) when [A] doubles
Order w.r.t A = 1

Compare Experiment 1 and 3 (A constant, B doubles):
Rate doubles (8.0/4.0 = 2) when [B] doubles
Order w.r.t B = 1

Answer: Order w.r.t A = 1, Order w.r.t B = 1

📝 Question 2: Colloids
Tyndall effect is observed in:
(A) True solution
(B) Colloidal solution
(C) Suspension
(D) Both colloidal solution and suspension

Solution:
Tyndall effect is the scattering of light by particles in a colloidal solution. It is observed in colloidal solutions where particle size is 1-1000 nm. True solutions have particles too small to scatter light, while suspensions have particles too large that settle down.

Answer: (B) Colloidal solution

2022 NEET Questions

📝 Question 1: Half Life Calculation
A first order reaction has rate constant 2.0 × 10⁻⁵ s⁻¹. Calculate the time required for 75% completion.

Solution:
For first order reaction:
t = (2.303/k) × log([A]₀/[A]t)

For 75% completion: [A]t = 25% of [A]₀
[A]₀/[A]t = 100/25 = 4

t = (2.303/2.0 × 10⁻⁵) × log(4)
t = 115150 × 0.602 = 69320 seconds

Answer: 69320 seconds

📝 Question 2: Adsorption
Which of the following statements about adsorption is correct?
(A) Adsorption is always endothermic
(B) Physisorption involves chemical bond formation
(C) Chemisorption is reversible
(D) Adsorption leads to decrease in surface energy

Solution:
- Adsorption is generally exothermic (surface energy decreases)
- Physisorption involves weak van der Waals forces
- Chemisorption is generally irreversible
- Adsorption decreases surface energy (more stable state)

Answer: (D) Adsorption leads to decrease in surface energy

🎯 Common Question Patterns

Pattern 1: Rate Law Determination

📊 Typical Structure:
- Given: Experimental data (concentrations and rates)
- Required: Determine rate law and order
- Method: Compare experiments systematically

🔢 Steps:
1. Write general rate law: Rate = k[A]^m[B]^n
2. Compare experiments keeping one concentration constant
3. Determine order for each reactant
4. Write complete rate law
5. Calculate rate constant if needed

Pattern 2: Half-Life Calculations

📊 Typical Structure:
- Given: Rate constant or half-life
- Required: Calculate time for certain completion
- Method: Apply appropriate integrated rate equation

🔢 Formulas:
- First order: t₁/₂ = 0.693/k
- Zero order: t₁/₂ = [A]₀/(2k)
- Second order: t₁/₂ = 1/(k[A]₀)

Pattern 3: Arrhenius Equation Applications

📊 Typical Structure:
- Given: Rate constants at different temperatures
- Required: Calculate activation energy
- Method: Apply Arrhenius equation

🔢 Formula:
log(k₂/k₁) = Ea/(2.303R) × (1/T₁ - 1/T₂)

⚠️ Common Mistakes and Solutions

Mistake 1: Order vs Molecularity

❌ Common Error:
- Confusing order with molecularity
- Assuming order equals stoichiometric coefficient
- Not recognizing fractional orders

✅ Correct Approach:
- Order is determined experimentally
- May differ from stoichiometric coefficients
- Can be zero, fractional, or integer
- Molecularity is always integer

Mistake 2: Integrated Rate Equations

❌ Common Error:
- Using wrong equation for given order
- Incorrect logarithm base
- Unit conversion errors

✅ Correct Approach:
- Use correct equation for reaction order
- Natural log (ln) or log base 10 as appropriate
- Maintain consistent units throughout

Mistake 3: Arrhenius Equation

❌ Common Error:
- Wrong temperature conversion
- Incorrect sign in exponent
- Unit errors in activation energy

✅ Correct Approach:
- Always use Kelvin temperature
- Remember negative sign in exponent
- Convert between J/mol and kJ/mol appropriately

🔧 Problem-Solving Strategies

Rate Law Problems

📝 Systematic Approach:
1. Write general rate law expression
2. Compare experiments systematically
3. Calculate order for each reactant
4. Verify with all experimental data
5. Write complete rate law
6. Calculate rate constant if required

Kinetic Calculations

📝 Step-by-Step Method:
1. Identify reaction order
2. Select appropriate integrated equation
3. Substitute known values
4. Solve for unknown quantity
5. Check units and reasonableness

Surface Chemistry Problems

📝 Problem-Solving Method:
1. Identify type of process (adsorption, catalysis)
2. Apply appropriate concepts
3. Use relevant formulas
4. Consider practical applications

📚 Practice Questions by Difficulty

Easy Level (Foundation Building)

📝 Practice Set 1:
1. Define order of reaction.
2. What is the unit of rate constant for zero order reaction?
3. Name two factors affecting rate of reaction.
4. What is Tyndall effect?
5. Define catalyst.

🎯 Expected Time: 30-45 seconds per question
💡 Focus: Basic concept recall

Medium Level (Concept Application)

📝 Practice Set 2:
1. For first order reaction, if k = 2.0 × 10⁻³ min⁻¹, calculate t₁/₂.
2. Determine order from data: A(0.1, rate 2), A(0.2, rate 4).
3. Calculate activation energy if rate constant doubles from 300K to 310K.
4. Differentiate between physisorption and chemisorption.
5. What happens when colloidal solution is electrolyzed?

🎯 Expected Time: 1-2 minutes per question
💡 Focus: Formula application and comparison

Hard Level (Advanced Problems)

📝 Practice Set 3:
1. For reaction A + B → C, when [A] doubles, rate quadruples; when [B] triples, rate triples. Find rate law.
2. Calculate time for 90% completion of first order reaction with k = 1.0 × 10⁻³ s⁻¹.
3. At what temperature will rate constant be 4 times its value at 300K (Ea = 50 kJ/mol)?
4. Explain mechanism of enzyme catalysis with lock and key model.
5. Calculate rate constant from Arrhenius plot with slope = -5000 K and intercept = 10.

🎯 Expected Time: 2-3 minutes per question
💡 Focus: Complex multi-step problems

📈 Performance Analysis

Success Rate by Question Type

📊 Success Rate Analysis:
- Basic definitions: 80% success rate
- Simple rate calculations: 70% success rate
- Order determination: 65% success rate
- Half-life problems: 60% success rate
- Arrhenius equation: 50% success rate
- Surface chemistry: 55% success rate

Time Management Analysis

⏱️ Average Time Taken:
- Easy questions: 30-45 seconds
- Medium questions: 1-2 minutes
- Hard questions: 2-3 minutes
- Very hard questions: 3-4 minutes

🎯 Recommended Time Allocation:
- Total 15-20 minutes for all kinetics questions
- Maximum 2 minutes per question
- Skip and return if taking longer

Common Error Analysis

📊 Error Categories:
1. Formula application errors: 25% of mistakes
2. Mathematical calculation errors: 20% of mistakes
3. Order determination errors: 20% of mistakes
4. Conceptual understanding errors: 20% of mistakes
5. Unit conversion errors: 15% of mistakes

🔧 Improvement Strategies:
- Master all kinetic formulas
- Practice mathematical calculations
- Learn systematic order determination
- Strengthen conceptual understanding
- Practice unit conversions

🎮 Interactive Learning Features

Formula Quick Reference

📋 Essential Formulas:
- First order: t₁/₂ = 0.693/k
- Zero order: t₁/₂ = [A]₀/(2k)
- Second order: t₁/₂ = 1/(k[A]₀)
- Arrhenius: log(k₂/k₁) = Ea/(2.303R) × (1/T₁ - 1/T₂)
- Integrated first order: log[A]t = log[A]₀ - (kt/2.303)
- Freundlich: x/m = kP^(1/n)

Important Constants

🔢 Key Values:
- R = 8.314 J·K⁻¹·mol⁻¹
- 2.303 (log conversion factor)
- 0.693 (ln 2)
- e = 2.718 (natural log base)

Catalyst Types

🚀 Classification:
- Positive catalyst: Increases rate
- Negative catalyst (poison): Decreases rate
- Auto-catalyst: Product acts as catalyst
- Enzyme: Biological catalyst

🔄 Regular Practice Schedule

Daily Practice Routine

📅 25-Minute Daily Session:
- 10 minutes: Rate law and order problems
- 10 minutes: Integrated rate equations
- 5 minutes: Surface chemistry concepts

📊 Weekly Progress:
- Day 1-2: Basic rate laws and order determination
- Day 3-4: Integrated rate equations and half-life
- Day 5-6: Arrhenius equation and temperature effects
- Day 7: Surface chemistry and revision

Monthly Assessment

📈 Monthly Goals:
- Master all rate law determinations
- Complete 40+ integrated rate equation problems
- Practice 30+ Arrhenius equation applications
- Learn surface chemistry concepts
- Achieve 75% accuracy in medium problems

✅ Self-Assessment Checklist

Concept Mastery Checklist

☐ Rate of reaction and factors affecting it
☐ Order and molecularity of reactions
☐ Rate laws and rate constants
☐ Integrated rate equations
☐ Half-life of reactions
☐ Temperature dependence (Arrhenius equation)
☐ Collision theory
☐ Catalysis and types of catalysts
☐ Adsorption (physisorption and chemisorption)
☐ Colloids and their properties
☐ Tyndall effect and Brownian motion
☐ Enzyme catalysis

Problem-Solving Skills

☐ Can determine rate laws from experimental data
☐ Can calculate order of reactions
☐ Can apply integrated rate equations
☐ Can calculate half-life and completion time
☐ Can use Arrhenius equation
☐ Can solve catalyst problems
☐ Can differentiate adsorption types
☐ Can identify colloidal properties
☐ Can handle multi-step problems
☐ Can complete within time limit

📊 Additional Resources

Rate Constant Units

📋 Units by Order:
- Zero order: mol·L⁻¹·s⁻¹
- First order: s⁻¹
- Second order: L·mol⁻¹·s⁻¹
- nth order: L^(n-1)·mol^(1-n)·s⁻¹

Colloidal Examples

🧪 Common Colloids:
- Sol: Paint, blood plasma
- Gel: Jelly, cheese
- Emulsion: Milk, butter
- Foam: Whipped cream, shaving cream
- Aerosol: Fog, smoke

Master chemical kinetics and surface chemistry with this comprehensive NEET PYQ collection! Build strong understanding of reaction rates, surface phenomena, and excel in Physical Chemistry! ⚡

Every reaction rate understood and surface phenomenon explored enhances your grasp of dynamic chemical processes! Begin your kinetics exploration today! 🚀