Chemical reactions don't just change substances - they also involve... Show more
Chemistry132 views·Updated May 20, 2026·2 pagesUnderstanding Exothermic and Endothermic Reactions
1
of 2
Exothermic & Endothermic Reactions
Ever wondered why hand warmers get hot or why some chemical reactions make things cold? It's all about energy transfer during chemical reactions.
Exothermic reactions are the energy releasers - they transfer energy from the reacting molecules to their surroundings, making the temperature around them increase. Think of combustion (burning), some oxidation reactions, and neutralisation reactions. In these reactions, the products end up with less energy than the reactants because energy has been given off to the surroundings.
Endothermic reactions work the opposite way - they're energy absorbers that take in energy from their surroundings, causing the temperature to drop. Thermal decomposition is a classic example. Here, the products have more energy than the reactants because they've absorbed energy from around them.
Real-world tip: Hand warmers and self-heating food cans use exothermic reactions to generate heat, whilst some instant cold packs use endothermic reactions to cool down!
2
of 2
Activation Energy
Not all particle collisions lead to chemical reactions - there's an energy barrier that must be overcome first.
Activation energy is the minimum amount of energy that particles must possess before they can react with each other. Think of it as the "entry fee" for a chemical reaction to occur. Particles need to collide with sufficient energy to break existing bonds and form new ones.
This concept applies to both exothermic and endothermic reactions. Even though exothermic reactions release energy overall, they still need that initial energy input to get started. It's like needing a spark to start a fire - once it begins, the fire releases much more energy than the spark provided.
Exam focus: Remember that activation energy is always required regardless of whether the overall reaction releases or absorbs energy!
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Chemistry132 views·Updated May 20, 2026·2 pagesUnderstanding Exothermic and Endothermic Reactions
Chemical reactions don't just change substances - they also involve energy changes that you can actually feel! Understanding whether a reaction releases or absorbs energy is crucial for predicting how reactions behave and explaining everyday phenomena like hand warmers and... Show more
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Exothermic & Endothermic Reactions
Ever wondered why hand warmers get hot or why some chemical reactions make things cold? It's all about energy transfer during chemical reactions.
Exothermic reactions are the energy releasers - they transfer energy from the reacting molecules to their surroundings, making the temperature around them increase. Think of combustion (burning), some oxidation reactions, and neutralisation reactions. In these reactions, the products end up with less energy than the reactants because energy has been given off to the surroundings.
Endothermic reactions work the opposite way - they're energy absorbers that take in energy from their surroundings, causing the temperature to drop. Thermal decomposition is a classic example. Here, the products have more energy than the reactants because they've absorbed energy from around them.
Real-world tip: Hand warmers and self-heating food cans use exothermic reactions to generate heat, whilst some instant cold packs use endothermic reactions to cool down!
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of 2Sign up to see the content. It's free!
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Activation Energy
Not all particle collisions lead to chemical reactions - there's an energy barrier that must be overcome first.
Activation energy is the minimum amount of energy that particles must possess before they can react with each other. Think of it as the "entry fee" for a chemical reaction to occur. Particles need to collide with sufficient energy to break existing bonds and form new ones.
This concept applies to both exothermic and endothermic reactions. Even though exothermic reactions release energy overall, they still need that initial energy input to get started. It's like needing a spark to start a fire - once it begins, the fire releases much more energy than the spark provided.
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