Boxi Learn › Chemistry › Stage 4 · Systems and Argument
Where reaction heat comes from
CHEM-3 Reactions trade energyCHEM-1 Atoms are rearranged, never lost
What many people think
Breaking a chemical bond releases energy.
The idea
Breaking bonds costs energy and making bonds releases it; a reaction is exothermic when the new bonds are stronger.
Explain it
A friend says: “Food gives you energy because the bonds in sugar break and release it.” Use bond energies to explain what really happens.
Try at home
With an adult: measure the temperature of some vinegar, stir in a spoon of baking soda and measure again (it gets a little colder). Then open a disposable hand warmer and feel it heat up. Which reaction makes stronger bonds than it breaks?