How It Works: Why Energy is Released
Part of Exothermic Reactions — GCSE Chemistry
This how it works covers How It Works: Why Energy is Released within Exothermic Reactions for GCSE Chemistry. Revise Exothermic Reactions in Energy Changes for GCSE Chemistry with 20 exam-style questions and 14 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 3 of 12 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 3 of 12
Practice
20 questions
Recall
14 flashcards
⚙️ How It Works: Why Energy is Released
Every chemical reaction involves breaking existing bonds in the reactants and forming new bonds in the products. Breaking bonds always requires energy (it is endothermic). Forming new bonds always releases energy (it is exothermic).
In an exothermic reaction, the energy released when NEW bonds form in the products is GREATER than the energy needed to break the OLD bonds in the reactants. The "surplus" energy is released to the surroundings as heat (and sometimes light). This is why the temperature of the surroundings increases — the reaction is literally warming up everything around it.
Think of it this way: the new bonds being made in the products are stronger (more stable) than the old bonds that were broken. Strong bonds hold atoms more tightly, and when atoms snap into a more stable arrangement, they release the extra energy as heat. Combustion is a perfect example — the C=O bonds in CO₂ and the O-H bonds in water are much stronger than the C-H and C-C bonds in the original fuel, so vast amounts of energy are released.