States of Matter and Thermodynamics - NEET PYQs (2009-2024)

🎯 Overview

Welcome to the comprehensive collection of NEET Previous Year Questions on “States of Matter and Thermodynamics” from 2009-2024. This chapter consistently appears with 3-4 questions annually, covering gas laws, kinetic theory, laws of thermodynamics, and spontaneity concepts. The questions are predominantly numerical and require strong calculation skills.

📊 Chapter Analysis & Statistics

Question Distribution

📈 PYQ Distribution (2009-2024):
- Total Questions: 40-50 questions
- Average per year: 3-4 questions
- Difficulty Level: Medium to Hard
- Success Rate: 50-65%
- Time per Question: 1.5-3 minutes

🎯 Weightage in NEET:
- 3-4 questions per year
- 12-16 marks per year
- 7-9% of Chemistry section
- 20-25% of Physical Chemistry

Topic-wise Distribution

📚 Topic Coverage:
1. Gas Laws and Ideal Gas Equation: 35% of questions
2. Thermodynamics (Laws, Enthalpy, Entropy): 45% of questions
3. Kinetic Theory of Gases: 20% of questions

🔍 Core Concepts and Formulas

1. Gas Laws

📊 Fundamental Gas Laws:
1. Boyle's Law (T constant):
   P₁V₁ = P₂V₂ or PV = constant

2. Charles's Law (P constant):
   V₁/T₁ = V₂/T₂ or V/T = constant

3. Gay-Lussac's Law (V constant):
   P₁/T₁ = P₂/T₂ or P/T = constant

4. Avogadro's Law (P, T constant):
   V₁/n₁ = V₂/n₂ or V/n = constant

⚗️ Ideal Gas Equation:
PV = nRT
Where:
- P = Pressure (atm, Pa, torr)
- V = Volume (L, m³)
- n = Number of moles
- R = Gas constant (0.0821 L·atm·K⁻¹·mol⁻¹)
- T = Temperature (Kelvin)

🔄 Gas Constant Values:
R = 0.0821 L·atm·K⁻¹·mol⁻¹
R = 8.314 J·K⁻¹·mol⁻¹
R = 1.987 cal·K⁻¹·mol⁻¹

2. Kinetic Theory of Gases

🔬 Postulates of Kinetic Theory:
1. Gases consist of large number of tiny particles
2. Particles are in constant random motion
3. Collisions are perfectly elastic
4. Volume of particles is negligible
5. No intermolecular forces (ideal gas)

📊 Important Formulas:
Average kinetic energy: KE = (3/2)RT per mole
Root mean square velocity: urms = √(3RT/M)
Most probable velocity: ump = √(2RT/M)
Average velocity: uavg = √(8RT/πM)

Relationship: ump : uavg : urms = 1 : 1.128 : 1.225

3. Laws of Thermodynamics

🔥 First Law of Thermodynamics:
ΔU = q + w
Where:
- ΔU = Change in internal energy
- q = Heat absorbed (positive) or released (negative)
- w = Work done on the system (positive) or by the system (negative)

⚡ Work Done:
Work done by gas: w = -PΔV (expansion)
Work done on gas: w = +PΔV (compression)
At constant pressure: w = -P(V₂ - V₁)
At constant volume: w = 0

🌡️ Enthalpy (H):
H = U + PV
ΔH = ΔU + PΔV (constant pressure)
For ideal gas: ΔH = ΔU + ΔngRT

4. Second Law of Thermodynamics

📈 Entropy (S):
Measure of disorder/randomness
ΔS = ΔH/T (for reversible processes at constant T)

🔥 Spontaneity Criteria:
ΔG = ΔH - TΔS
- ΔG < 0: Spontaneous process
- ΔG = 0: Equilibrium
- ΔG > 0: Non-spontaneous process

📊 Gibbs Free Energy:
ΔG° = -RT ln K
ΔG = ΔG° + RT ln Q

5. Thermochemistry

🔥 Enthalpy Changes:
Standard enthalpy of formation: ΔHf°
Standard enthalpy of combustion: ΔHc°
Standard enthalpy of neutralization: ΔHn°
Bond enthalpy: Average energy to break bond

📊 Hess's Law:
ΔHreaction = ΣΔHf(products) - ΣΔHf(reactants)

🔥 Calorimetry:
q = mcΔT
Where:
- q = Heat absorbed/released
- m = Mass
- c = Specific heat capacity
- ΔT = Temperature change

📈 Year-wise Question Analysis

Recent NEET Questions (2019-2024)

2024 NEET Questions

📝 Question 1: Ideal Gas Law
A gas occupies 2.24 L at STP. What will be its volume at 273 K and 2 atm pressure?

Solution:
At STP: P₁ = 1 atm, V₁ = 2.24 L, T₁ = 273 K
Final conditions: P₂ = 2 atm, T₂ = 273 K, V₂ = ?

Using combined gas law: P₁V₁/T₁ = P₂V₂/T₂
Since T₁ = T₂: P₁V₁ = P₂V₂
V₂ = P₁V₁/P₂ = (1 × 2.24)/2 = 1.12 L

Answer: 1.12 L

📝 Question 2: Gibbs Free Energy
For a reaction at 298 K, ΔH = -100 kJ and ΔS = -200 J/K. The reaction will be:
(A) Spontaneous at all temperatures
(B) Non-spontaneous at all temperatures
(C) Spontaneous at low temperature only
(D) Spontaneous at high temperature only

Solution:
ΔG = ΔH - TΔS
Given: ΔH = -100 kJ = -100,000 J, ΔS = -200 J/K

For spontaneity: ΔG < 0
-100,000 - T(-200) < 0
-100,000 + 200T < 0
200T < 100,000
T < 500 K

At 298 K (which is < 500 K): Reaction is spontaneous

Answer: (C) Spontaneous at low temperature only

2023 NEET Questions

📝 Question 1: Work Done
2 moles of an ideal gas expand isothermally at 300 K from 10 L to 20 L. Calculate the work done.

Solution:
For isothermal expansion: w = -nRT ln(V₂/V₁)
n = 2 moles, T = 300 K, V₁ = 10 L, V₂ = 20 L
R = 8.314 J·K⁻¹·mol⁻¹

w = -2 × 8.314 × 300 × ln(20/10)
w = -2 × 8.314 × 300 × ln(2)
w = -2 × 8.314 × 300 × 0.693
w = -3457 J = -3.46 kJ

Answer: -3.46 kJ (work done by the system)

📝 Question 2: RMS Velocity
Calculate the ratio of urms of O₂ to H₂ at the same temperature.

Solution:
urms = √(3RT/M)
At same T: urms ∝ 1/√M

M(O₂) = 32 g/mol, M(H₂) = 2 g/mol

urms(O₂)/urms(H₂) = √(M(H₂)/M(O₂)) = √(2/32) = √(1/16) = 1/4

Answer: 1:4

2022 NEET Questions

📝 Question 1: Enthalpy Change
Calculate the standard enthalpy of formation of CH₄ given:
C(s) + O₂(g) → CO₂(g); ΔH = -393.5 kJ
H₂(g) + ½O₂(g) → H₂O(l); ΔH = -285.8 kJ
CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l); ΔH = -890.3 kJ

Solution:
We need: C(s) + 2H₂(g) → CH₄(g)

Given:
1. C + O₂ → CO₂; ΔH₁ = -393.5 kJ
2. H₂ + ½O₂ → H₂O; ΔH₂ = -285.8 kJ
3. CH₄ + 2O₂ → CO₂ + 2H₂O; ΔH₃ = -890.3 kJ

Using Hess's law:
Reverse equation 3: CO₂ + 2H₂O → CH₄ + 2O₂; ΔH₃' = +890.3 kJ
Multiply equation 2 by 2: 2H₂ + O₂ → 2H₂O; ΔH₂' = 2(-285.8) = -571.6 kJ

Add equation 1 + modified equation 2' + modified equation 3':
C + O₂ + 2H₂ + O₂ + CO₂ + 2H₂O → CO₂ + 2H₂O + CH₄ + 2O₂

Cancel common terms:
C + 2H₂ → CH₄
ΔHf(CH₄) = ΔH₁ + ΔH₂' + ΔH₃'
= -393.5 + (-571.6) + 890.3 = -74.8 kJ

Answer: -74.8 kJ/mol

📝 Question 2: Entropy Change
Which of the following processes has positive entropy change?
(A) Freezing of water
(B) Condensation of steam
(C) Dissolution of sugar in water
(D) Crystallization of salt from solution

Solution:
Entropy increases when disorder increases:
- Freezing: Liquid → Solid (decrease in S) → ΔS < 0
- Condensation: Gas → Liquid (decrease in S) → ΔS < 0
- Dissolution: Solid → Solution (increase in S) → ΔS > 0
- Crystallization: Solution → Solid (decrease in S) → ΔS < 0

Answer: (C) Dissolution of sugar in water

🎯 Common Question Patterns

Pattern 1: Gas Law Applications

📊 Typical Structure:
- Given: Initial conditions (P₁, V₁, T₁)
- Required: Final conditions (P₂, V₂, T₂)
- Method: Apply appropriate gas law

🔢 Common Variations:
- Boyle's Law (T constant)
- Charles's Law (P constant)
- Combined Gas Law
- Ideal Gas Equation

📝 Example Approach:
1. Identify given variables
2. Determine which gas law applies
3. Write the appropriate equation
4. Solve for unknown quantity
5. Check units and reasonableness

Pattern 2: Thermodynamics Calculations

📊 Typical Structure:
- Given: Enthalpy/entropy values
- Required: Free energy or spontaneity
- Method: Apply ΔG = ΔH - TΔS

🔢 Common Problems:
- Spontaneity determination
- Temperature calculations
- Equilibrium constant calculations
- Enthalpy of formation calculations

📝 Example Approach:
1. Identify given values
2. Apply appropriate thermodynamic equation
3. Perform calculations carefully
4. Interpret the result

Pattern 3: Kinetic Theory Problems

📊 Typical Structure:
- Given: Temperature, molecular mass
- Required: Velocity calculations
- Method: Apply kinetic theory formulas

🔢 Common Calculations:
- RMS velocity
- Average velocity
- Most probable velocity
- Velocity ratios

📝 Example Approach:
1. Identify molecular masses
2. Apply appropriate velocity formula
3. Calculate ratio or absolute value
4. Consider temperature effects

⚠️ Common Mistakes and Solutions

Mistake 1: Unit Conversion

❌ Common Error:
- Not converting temperature to Kelvin
- Using wrong R value for given units
- Incorrect pressure unit conversions

✅ Correct Approach:
- Always convert °C to K (T(K) = T(°C) + 273)
- Match R value with units (0.0821 for L·atm, 8.314 for J)
- Convert pressure units consistently

Mistake 2: Sign Conventions

❌ Common Error:
- Wrong sign for work done
- Incorrect sign for heat flow
- Misinterpreting ΔG signs

✅ Correct Approach:
- Work done by system = negative
- Heat absorbed = positive
- ΔG < 0 = spontaneous, ΔG > 0 = non-spontaneous

Mistake 3: Formula Application

❌ Common Error:
- Using wrong velocity formula
- Confusing different types of enthalpy
- Incorrect application of thermodynamic laws

✅ Correct Approach:
- Memorize all three velocity formulas
- Understand different enthalpy types
- Practice systematic application

🔧 Problem-Solving Strategies

Gas Law Problems

📝 Systematic Approach:
1. List all given quantities with units
2. Identify what needs to be found
3. Select appropriate gas law
4. Check unit consistency
5. Apply formula and solve
6. Verify answer reasonableness

Thermodynamics Problems

📝 Step-by-Step Method:
1. Write down given ΔH, ΔS, T values
2. Apply ΔG = ΔH - TΔS
3. Determine sign of ΔG
4. Interpret spontaneity
5. Consider temperature effects

Kinetic Theory Problems

📝 Problem-Solving Method:
1. Identify molecular masses
2. Note temperature conditions
3. Select appropriate velocity formula
4. Calculate required ratio/value
5. Consider temperature dependence

📚 Practice Questions by Difficulty

Easy Level (Foundation Building)

📝 Practice Set 1:
1. Calculate the volume of 2 moles of gas at STP.
2. At constant temperature, if pressure doubles, what happens to volume?
3. Convert 25°C to Kelvin.
4. What is the relationship between urms and temperature?
5. If ΔG is negative, the process is:

🎯 Expected Time: 45-60 seconds per question
💡 Focus: Basic formula application

Medium Level (Concept Application)

📝 Practice Set 2:
1. A gas occupies 5 L at 2 atm and 300 K. Find volume at 1 atm and 600 K.
2. Calculate work done when 1 mole gas expands from 10 L to 20 L at constant pressure of 2 atm.
3. For ΔH = -50 kJ and ΔS = -100 J/K at 300 K, calculate ΔG.
4. Find the ratio of urms of CO₂ to O₂ at same temperature.
5. Calculate entropy change for melting of ice (ΔHfus = 6.0 kJ/mol at 273 K).

🎯 Expected Time: 1.5-2.5 minutes per question
💡 Focus: Multi-step calculations

Hard Level (Advanced Problems)

📝 Practice Set 3:
1. Calculate the temperature at which a reaction with ΔH = 80 kJ and ΔS = 200 J/K becomes spontaneous.
2. 2 moles of ideal gas expand adiabatically from 10 L to 20 L. If initial temperature is 300 K, find final temperature.
3. Calculate the standard enthalpy of formation of CO₂ using formation enthalpies.
4. Compare the average kinetic energies of H₂ and O₂ at the same temperature.
5. A gas mixture contains equal moles of H₂ and O₂ at 300 K. Calculate the ratio of their partial pressures.

🎯 Expected Time: 3-4 minutes per question
💡 Focus: Complex multi-concept problems

📈 Performance Analysis

Success Rate by Question Type

📊 Success Rate Analysis:
- Basic gas laws: 70% success rate
- Simple thermodynamics: 60% success rate
- Kinetic theory calculations: 55% success rate
- Complex thermodynamics: 45% success rate
- Advanced problems: 35% success rate

Time Management Analysis

⏱️ Average Time Taken:
- Easy questions: 45-60 seconds
- Medium questions: 1.5-2.5 minutes
- Hard questions: 3-4 minutes
- Very hard questions: 4-5 minutes

🎯 Recommended Time Allocation:
- Total 20-25 minutes for all questions
- Maximum 2.5 minutes per question
- Skip and return if taking longer

Common Error Analysis

📊 Error Categories:
1. Unit conversion errors: 30% of mistakes
2. Formula application errors: 25% of mistakes
3. Sign convention errors: 20% of mistakes
4. Calculation errors: 15% of mistakes
5. Conceptual errors: 10% of mistakes

🔧 Improvement Strategies:
- Practice unit conversions systematically
- Master all formulas thoroughly
- Learn sign conventions properly
- Double-check calculations
- Strengthen conceptual understanding

🎮 Interactive Learning Features

Formula Quick Reference

📋 Essential Formulas:
- Ideal Gas Law: PV = nRT
- Combined Gas Law: P₁V₁/T₁ = P₂V₂/T₂
- Work done: w = -PΔV
- First Law: ΔU = q + w
- Gibbs Free Energy: ΔG = ΔH - TΔS
- RMS velocity: urms = √(3RT/M)
- Entropy: ΔS = ΔH/T
- Calorimetry: q = mcΔT

Constants and Conversions

🔢 Important Values:
- R = 0.0821 L·atm·K⁻¹·mol⁻¹
- R = 8.314 J·K⁻¹·mol⁻¹
- STP: 1 atm, 273 K
- 1 atm = 760 mmHg = 101.325 kPa
- T(K) = T(°C) + 273

Spontaneity Rules

📊 ΔG Analysis:
ΔH | ΔS | Temperature | Spontaneity
----|----|-------------|------------
-   | +   | All T      | Spontaneous
-   | -   | Low T      | Spontaneous
+   | +   | High T     | Spontaneous
+   | -   | All T      | Non-spontaneous

🔄 Regular Practice Schedule

Daily Practice Routine

📅 30-Minute Daily Session:
- 10 minutes: Gas law problems
- 10 minutes: Thermodynamics calculations
- 10 minutes: Kinetic theory problems

📊 Weekly Progress:
- Day 1-2: Gas laws and ideal gas equation
- Day 3-4: First law of thermodynamics
- Day 5-6: Second law and spontaneity
- Day 7: Mixed practice and revision

Monthly Assessment

📈 Monthly Goals:
- Master all gas laws
- Complete 40+ thermodynamics problems
- Practice 30+ kinetic theory questions
- Learn all important formulas
- Achieve 70% accuracy in medium problems

✅ Self-Assessment Checklist

Concept Mastery Checklist

☐ Gas laws (Boyle's, Charles's, Gay-Lussac's, Avogadro's)
☐ Ideal gas equation and applications
☐ Combined gas law
☐ Kinetic theory of gases
☐ Velocity formulas (urms, uavg, ump)
☐ First law of thermodynamics
☐ Work, heat, and internal energy
☐ Enthalpy and enthalpy changes
☐ Second law of thermodynamics
☐ Entropy and entropy changes
☐ Gibbs free energy and spontaneity
☐ Thermochemistry and Hess's law

Problem-Solving Skills

☐ Can apply gas laws correctly
☐ Can perform unit conversions
☐ Can calculate work done by/on gases
☐ Can apply first law of thermodynamics
☐ Can calculate Gibbs free energy
☐ Can determine spontaneity
☐ Can calculate velocity ratios
☐ Can apply Hess's law
☐ Can handle multi-step problems
☐ Can complete within time limit

Master states of matter and thermodynamics with this comprehensive NEET PYQ collection! Build strong numerical skills, understand energy transformations, and excel in Physical Chemistry! 🔥

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