11 Oct 2026
Exothermic And Endothermic Reactions IGCSE Examples
Based on the Cambridge IGCSE Chemistry 0620 syllabus for exams in 2026, 2027 and 2028 (Version 2). Always confirm details on the official Cambridge website.
Written by an experienced chemistry teacher.
Last updated: October 2026.
Quick Answer Box
Exothermic reactions give out heat energy to the surroundings, causing the temperature to rise. Endothermic reactions take in heat energy from the surroundings, causing the temperature to drop. In Cambridge IGCSE Chemistry 0620, knowing these energy changes helps you pass your exams.
Table of Contents
What Are Exothermic And Endothermic Reactions? [Core + Extended]
Do you know how heat moves during chemical changes? Exothermic and endothermic reactions show how energy flows between chemicals and the world around them. When chemical bonds break or form, energy moves.
Exothermic: heat goes OUT, the surroundings get hotter. If you touch the test tube, it feels hot. Burning wood in a campfire is a classic chemical reaction that releases heat energy.
Endothermic: heat goes IN, the surroundings get colder. If you touch the container, it feels cold. Thermal decomposition of limestone is a chemical reaction that absorbs heat energy.
Melting ice cubes take in warmth from the air. That is a physical process, not a chemical reaction. Students often lose marks when they confuse temperature changes with heat changes.
For complete syllabus details, check the official Cambridge Assessment International Education website. You can also review our [internal link: pillar page] for more study materials.
Step-by-Step Explanation [Extended]
To fully understand how these reactions work, follow this step-by-step breakdown of particle behavior and energy flow:
Particle Collision: Reactant particles must collide with each other with enough speed and energy for a reaction to begin.
Breaking Old Bonds: Energy must be taken in from the surroundings to break the bonds holding the reactant atoms together. This step is always endothermic.
Forming New Bonds: New bonds form between atoms to create products. This step releases energy back into the surroundings and is always exothermic.
Net Energy Balance: If more energy is released making bonds than was used breaking them, the overall reaction is exothermic and ΔH is negative. If more energy is absorbed breaking bonds than is released making them, the reaction is endothermic and ΔH is positive.
Worked Examples [Extended]
Exam questions often test your understanding using practical chemical calculations. Here is a complete worked calculation example:
Scenario: Consider the combustion of hydrogen gas in oxygen to form water: 2H₂ + O₂ -> 2H₂O.
Bond Energies: H-H is 436 kJ/mol, O=O is 498 kJ/mol, O-H is 464 kJ/mol.
Step 1 (Break Bonds): Energy to break 2 moles of H-H and 1 mole of O=O is (2 x 436) + 498 = 872 + 498 = 1370 kJ.
Step 2 (Form Bonds): Energy released making 4 moles of O-H bonds is 4 x 464 = 1856 kJ.
Step 3 (Calculate ΔH): ΔH = Energy in (break) - Energy out (make) = 1370 - 1856 = -486 kJ/mol.
Final Answer: The enthalpy change is -486 kJ/mol, confirming the reaction is exothermic.
Diagram Guide [Core + Extended]
Reaction pathway diagrams are vital for showing energy changes visually. Here is how to draw and label them correctly:
Axes Setup: Draw a vertical y-axis labeled "Energy" and a horizontal x-axis labeled "Progress of reaction".
Reactants Line: Draw a horizontal line on the left representing the energy level of the reactants.
Activation Energy Hill: Draw a curved hill going upward from the reactants line to show the Eₐ barrier.
Products Line: For an exothermic reaction, draw the products line below the reactants line. For an endothermic reaction, draw the products line above the reactants line.
Enthalpy Arrow: Draw a vertical double-headed arrow between the reactants and products level and label it as ΔH.
Practical Skills [Core + Extended]
When studying heat changes in the lab, you must follow strict experimental procedures. Here is how to investigate a neutralization reaction safely:
Apparatus: Polystyrene cup, glass beaker, thermometer, measuring cylinder, hydrochloric acid, sodium hydroxide solution.
Steps: Measure 25 cm³ of acid into the polystyrene cup. Record its initial temperature. Add 25 cm³ of alkali and stir gently with the thermometer. Record the highest temperature reached.
Safety Points: Wear safety goggles and a lab coat. Avoid skin contact with dilute acids.
Measurements and Recording: Record initial temperature, final temperature, and calculate the temperature change in a structured results table.
Graphing and Conclusion: Plot temperature change against volume added. Conclude that neutralization is exothermic because heat energy transfers to the liquid, raising its temperature.
Past Paper Question Types [Core + Extended]
Part A: Question Types You Will See
Drawing a Diagram: Sketching energy pathways with labeled Eₐ and ΔH arrows. How to answer: ensure peaks and product lines align correctly. Common mistake: starting activation energy from products.
Doing a Calculation: Working out bond energy sums. How to answer: list bond values, compute breaking and making totals separately. Common mistake: mixing up math signs.
Reading a Graph: Interpreting temperature traces. How to answer: locate peak values carefully. Common mistake: reading initial baseline incorrectly.
Planning an Experiment: Describing calorimeter setups. How to answer: mention insulation and stirring. Common mistake: forgetting heat loss precautions.
Part C: How to Practise
Review core definitions every morning.
Sketch ten pathway diagrams from memory.
Complete five bond energy calculation sums.
Check your answers against official mark schemes.
Fix any errors in a dedicated revision notebook.
Time yourself on a 15-minute energetics mini-test.
Common Mistakes [Core + Extended]
Students frequently lose easy marks on energetics questions by making these avoidable errors:
Saying that heat is created or coldness is produced instead of explaining that heat energy is transferred.
Starting the activation energy arrow from the top of the curve instead of the reactant energy level.
Forgetting to write the positive or negative sign in front of the enthalpy change value.
Making arithmetic errors when adding up bond breaking and bond making energies.
Confusing physical melting processes with chemical exothermic reactions.
Writing incorrect units for enthalpy change calculations.
Quick Revision Notes [Core + Extended]
Exothermic reactions release heat energy, cause temperatures to rise, and have a negative ΔH.
Endothermic reactions absorb heat energy, cause temperatures to drop, and have a positive ΔH.
Bond breaking absorbs energy, while bond making releases energy.
Eₐ is the minimum energy required for colliding particles to react.
Polystyrene cups provide good insulation during neutralization experiments.
Combustion and respiration are key everyday examples of exothermic changes.
Thermal decomposition requires a continuous supply of heat energy.
Always check the official syllabus for exact paper formats and current assessment guidelines.
Student Checklist [Core + Extended]
[ ] Memorized definitions for exothermic and endothermic reactions
[ ] Can interpret and draw reaction pathway diagrams with correct energy levels
[ ] Understands why bond breaking is endothermic and bond making is exothermic
[ ] Practiced bond energy math calculations with correct units
[ ] Reviewed practical steps for polystyrene cup calorimeter tests
[ ] Memorized command words and how to answer them
[ ] Completed past paper questions on chemical energetics
[ ] Reviewed all revision notes before test day
[ ] Prepared pencils, pens, and calculator for exam morning
[ ] Got a good night of sleep before the exam paper
Frequently Asked Questions [Core + Extended]
What is an exothermic reaction in IGCSE Chemistry?
An exothermic reaction is a chemical process that transfers heat energy to the surroundings. This transfer leads to an increase in the temperature of those surroundings. Common examples include combustion and neutralization reactions between acids and alkalis.
What is an endothermic reaction in simple terms?
An endothermic reaction takes in heat energy from the surroundings. This absorption leads to a noticeable decrease in the temperature of those surroundings. Everyday examples include thermal decomposition of limestone and sports instant cold packs.
How do you identify an exothermic reaction from its enthalpy change?
You can identify an exothermic reaction because its enthalpy change value, written as ΔH, is negative. This negative sign indicates that energy has been released from the chemical system into the surrounding environment during the chemical reaction.
What does activation energy mean in chemical energetics?
Activation energy, represented as Eₐ, is defined as the minimum amount of energy that colliding reactant particles must possess in order for a chemical reaction to successfully take place. Catalysts help speed up reactions by lowering this required activation energy threshold.
Why is bond breaking considered an endothermic process?
Bond breaking is an endothermic process because energy must be absorbed from the surroundings to overcome the strong forces holding the bonded atoms together. Conversely, forming new chemical bonds releases energy, making bond making an exothermic process.
How do you calculate enthalpy change using bond energies?
To calculate the enthalpy change of a reaction, you sum the total energy required to break all bonds in the reactants and subtract the total energy released when new bonds form in the products. This gives you the net energy change for the transformation.
What are common everyday examples of exothermic processes?
Common everyday examples of exothermic processes include burning fossil fuels, the reaction of water with quicklime, and hand warmers that rely on iron oxidation. These processes always transfer heat outward into the immediate environment.
How do reaction pathway diagrams show energy changes?
Reaction pathway diagrams show energy changes by plotting energy levels on the y-axis against reaction progress on the x-axis. They illustrate whether products sit lower than reactants for exothermic changes or higher for endothermic changes alongside the activation energy peak.
Key Takeaways [Core + Extended]
Exothermic reactions release heat energy and feature negative enthalpy changes.
Endothermic reactions absorb heat energy and feature positive enthalpy changes.
Bond breaking requires energy intake, whereas bond formation releases energy outward.
Mastering reaction pathway diagrams and bond calculations secures top exam marks.
Safety precautions are essential during lab calorimeter experiments.
Temperature measures surroundings while ΔH measures the chemical system.
Regular past paper practice builds confidence for exam day.
Final Thoughts [Core + Extended]
Studying chemical energetics gives you a solid foundation in Cambridge IGCSE Chemistry. Keep practicing your pathway diagrams and calculation steps regularly. Review past paper questions today and build complete confidence for your exam!