IGCSE Chemistry 0620 | Chemical Energetics Past Paper | Graph based Questions Numericals

We do a thorough, exam-oriented revision of the chapter Chemical Energetics using actual Board-level questions, many of them taken directly from the 2025 Board Papers in this lecture. The session is designed to help you recognize question patterns, understand the logic, and solve both MCQs and numericals with confidence.

00:00 Welcome & Overview – What to Expect in This Chemical Energetics Lecture
01:50 Quick Revision: Endothermic vs Exothermic Reactions (Must Understand!)
07:55 Type 1 MCQs – Identifying Graphs
14:50 Type 2 _ Calculating Enthalpy Numericals
25:40 Numerical 2 _ Enthalpy
33:20 Numerical 3 _ Enthalpy
41:30 Numerical 4 _ Enthalpy

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What this lecture covers:
1⃣ Core concepts of Chemical Energetics (Quick Revision)
System vs surroundings
Energy entering vs leaving the system
Sign convention for energy changes
Bond breaking (energy absorbed, +ve)
Bond formation (energy released, –ve)
Clear meaning of ΔH (enthalpy change)

2⃣ Endothermic vs Exothermic Reactions – Made Intuitive
Why energy is absorbed in endothermic reactions
Why energy is released in exothermic reactions
Real-life analogy to make concepts stick
Mnemonics to avoid confusion
Relation between:
Energy of reactants
Energy of products
Sign of ΔH

3⃣ Reaction Pathway Diagrams (Very Important for MCQs)
Identifying:
Exothermic vs endothermic reactions from graphs
Activation energy (Ea)
Enthalpy change (ΔH)
Labeling diagrams exactly as required in board exams
Questions asked directly in 2025 Board MCQs

4⃣ Activation Energy & Catalysts
Meaning of activation energy
Symbol used in textbooks (asked as 1-mark question)
Effect of catalyst:
Lowers activation energy
Does NOT change ΔH

5⃣ Bond Energy Calculations – Step by Step
Calculating ΔH using bond energies:
Energy required to break bonds (EB)
Energy released when new bonds form (EF)
Careful handling of:
Number of bonds
Number of moles
Correct signs (+ / –)
Multiple board-level numericals fully solved

6⃣ Combustion Reactions as Classic Examples
Why combustion reactions are always exothermic
Predicting sign of ΔH before calculation
Eliminating wrong MCQ options logically

7⃣ Advanced Board-Type Numericals
Questions where:
ΔH is given and bond energy is unknown
Bond energy is calculated using algebra (assuming unknown = x)
Problems asked in Feb–March 2025 Board Exams
Common mistakes students make—and how to avoid them

8⃣ Reactions Covered in Detail
Methane combustion
Formation of methane from atoms
Iodine–Bromine reactions
Iodine–Chlorine reactions
Carbonyl chloride (COCl₂) bond-energy problems
Each numerical is solved with:
Clear logic
Diagrams and visualization
Proper units (kJ mol⁻¹)
Exam-ready presentation
🎯 Who should watch this lecture?
Students revising Chemical Energetics for Board Exams
Those confused between endothermic and exothermic reactions
Students struggling with bond energy numericals
Anyone aiming for full marks in MCQs + numericals
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Disclaimer:
📝📝📝 While I have taken care to ensure the accuracy of the information presented, this channel assumes no responsibility or liability for any errors or omissions. You are requested to consult standard textbooks in case of any confusion.
Thank you.

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