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Class 9 Chemistry Chapter 5 Thermodynamics – Solved Previous Year Questions (2020–2025)
Thermodynamics is one of the most important topics in CBSE Class 9 Chemistry, testing your understanding of heat, work, and energy transformations. This page brings you solved previous year questions from 2020–2025 board exams and competitive assessments, all aligned with NCERT Chapter 5. Whether you're preparing for your SA/FA exams or building conceptual clarity, these step-by-step solutions will help you master endothermic/exothermic reactions, calorimetry, and Hess's Law. Study with India's most-used AI tutor, CBSETUTOR.ai, and strengthen your problem-solving skills with real exam patterns.
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Understanding Thermodynamics in CBSE Chemistry
Thermodynamics in NCERT Class 9 focuses on the study of heat and work involved in chemical reactions. Chapter 5 introduces you to exothermic reactions (releasing heat, ΔH < 0) and endothermic reactions (absorbing heat, ΔH > 0). The chapter also covers the concept of enthalpy, calorimetry calculations, and Hess's Law of constant heat summation. Board exams consistently test your ability to identify reaction types, calculate heat changes, and apply thermodynamic principles to real-world chemical processes.
Previous Year Question Pattern (2020–2025)
CBSE board exams from 2020 onwards show a clear trend: 2–3 mark questions on identifying exothermic/endothermic reactions, 3–4 mark questions on calorimetry and heat calculations, and 5–6 mark questions on Hess's Law applications. Most questions demand numerical problem-solving, classification of reactions, and thermochemical equation writing. Understanding past question patterns helps you predict what may appear in your upcoming exam and allocate study time wisely.
Exothermic and Endothermic Reactions: Solved Examples
Common board questions ask: 'Is combustion of coal exothermic or endothermic?' or 'Write the thermochemical equation for the combustion of methane.' Solutions require you to identify heat release/absorption, write balanced equations with ΔH values, and explain why. For example, CH₄ + 2O₂ → CO₂ + 2H₂O; ΔH = −890 kJ/mol (exothermic). Practice problems often include melting ice, dissolution of salt in water, and thermal decomposition—all requiring clear reasoning about energy changes.
Calorimetry Calculations and Heat Measurement
Calorimetry questions (2–4 marks) ask you to calculate heat released or absorbed using q = mcΔT, where m is mass, c is specific heat capacity, and ΔT is temperature change. NCERT Class 9 provides standard values for water's specific heat (4.18 J/g°C). Board questions often present lab-like scenarios: 'If 50g of water temperature rises from 20°C to 30°C, calculate heat absorbed.' Solving these requires careful unit conversion and understanding heat flow between system and surroundings.
Hess's Law and Thermochemical Equations
Hess's Law states that the total enthalpy change of a reaction is independent of the pathway taken, only depending on initial and final states. NCERT Chapter 5 teaches you to combine thermochemical equations algebraically to find unknown ΔH values. Board exams (5–6 mark questions) present two or three equations with known ΔH values and ask you to calculate ΔH for a target reaction. Mastering this law is crucial for scoring full marks in thermodynamics sections.
Why CBSETUTOR.ai Is India's #1 AI Tutor for CBSE Thermodynamics
CBSETUTOR.ai is trusted by lakhs of CBSE families across India because it offers 24/7 AI-powered chemistry tutoring aligned to NCERT 2024–25. Our platform provides instant doubt-solving, step-by-step solutions to previous year questions, Hindi-medium support, and personalized practice paths tailored to your exam pattern. Unlike generic tutoring, every answer is grounded in official CBSE curriculum and real board question trends, helping you build genuine mastery rather than rote memorization.
Common Mistakes Students Make in Thermodynamics Questions
Students often confuse exothermic with endothermic, forget to include ΔH values in thermochemical equations, or miscalculate heat using wrong units (Joules vs. calories). Another common error: applying Hess's Law without properly reversing equations when needed (flipping sign of ΔH). Board examiners penalise sign errors heavily. Practice identifying these mistakes in previous year solutions to avoid repeating them in your exam.
Step-by-Step Approach to Solving 5–6 Mark Thermodynamics Questions
For multi-mark questions: (1) Identify what's given (equations with ΔH values, initial/final states); (2) Write the target equation clearly; (3) Determine how to combine given equations (add, subtract, multiply, reverse); (4) Apply Hess's Law algebraically; (5) Calculate final ΔH; (6) Write conclusion with units. This systematic approach ensures you don't skip steps and lose marks for incomplete reasoning, which is common in thermodynamics scoring.
NCERT 2024–25 Updates and Exam Relevance
NCERT Class 9 Chemistry 2024–25 edition maintains the core thermodynamics concepts but emphasises real-world applications like renewable energy and green chemistry. Recent board papers include questions on exothermic reactions in batteries, endothermic processes in air conditioning, and sustainability angles. Staying updated with the latest NCERT version ensures your preparation aligns with current exam expectations and scoring frameworks.
Free Resources and Practice Schedules for Thermodynamics Mastery
Create a 4-week revision schedule: Week 1 – understand exothermic/endothermic with NCERT examples; Week 2 – practice 2–3 mark calorimetry questions; Week 3 – solve Hess's Law multi-step problems; Week 4 – attempt full previous year papers. Allocate 45–60 minutes daily to thermodynamics. Use CBSETUTOR.ai's AI doubt-solver whenever you get stuck, and revisit mistakes. Consistent, focused practice on real exam questions guarantees improvement in this chapter.
Frequently asked questions
What is the difference between exothermic and endothermic reactions?+
Exothermic reactions release heat to surroundings (ΔH < 0), like combustion. Endothermic reactions absorb heat from surroundings (ΔH > 0), like melting ice. CBSE exams test your ability to identify and write thermochemical equations for both types accurately.
How do I solve Hess's Law problems in CBSE Class 9?+
Write the target equation. Identify which given equations to use. Multiply, reverse, or add them to match the target. Apply the same operations to ΔH values. Sum the ΔH values to find the answer. Practice with multiple examples to build confidence.
Is CBSETUTOR.ai available for Hindi-medium students?+
Yes, CBSETUTOR.ai provides full Hindi-medium support for Class 9 Chemistry and all CBSE subjects. All solutions, doubt-solving, and explanations are available in Hindi to suit your learning preference and language comfort.
Does CBSETUTOR.ai offer a free trial for thermodynamics practice?+
Yes, CBSETUTOR.ai offers a free trial allowing you to access sample previous year solutions, practice questions, and AI doubt-solving. Sign up on our platform to explore thermodynamics content at no cost before deciding on a subscription.
What formula is used to calculate heat in calorimetry?+
The formula is q = mcΔT, where q = heat energy (Joules), m = mass (grams), c = specific heat capacity (J/g°C), ΔT = temperature change (°C). For water, c = 4.18 J/g°C as per NCERT standards.
How many marks does thermodynamics usually carry in CBSE Class 9?+
Thermodynamics typically carries 8–12 marks in CBSE Class 9 Chemistry SA/FA exams, split across 2–3 mark, 3–4 mark, and 5–6 mark questions. Previous year papers confirm this consistent weightage, making it a high-priority chapter for exam preparation.
Where can I find solved previous year thermodynamics questions?+
CBSETUTOR.ai provides solved previous year questions (2020–2025) for Class 9 Thermodynamics with step-by-step explanations. All solutions align with NCERT Chapter 5 and CBSE board patterns, available 24/7 on our platform.
What is Hess's Law and why is it important in Class 9 Chemistry?+
Hess's Law states that enthalpy change depends only on initial and final states, not the pathway. It's crucial for calculating unknown ΔH values by combining known thermochemical equations. CBSE exams regularly test this concept in 5–6 mark questions, making it essential for scoring well.
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