This mini-lesson walks you through energetics for KS3 Science: how energy changes when a substance changes state, what happens in exothermic and endothermic reactions, some everyday examples, and the big idea that breaking and making bonds involves energy.
Work through each screen, answer the questions as you go and collect ⭐ stars. Press Start when you're ready.
Whenever matter changes state or a chemical reaction happens, energy is either taken in from the surroundings or given out to them. We usually notice this as a change in temperature.
Golden rule: energy is never made or destroyed — it only moves between the chemicals and their surroundings. This is called conservation of energy.
To go from a more ordered state to a more spread-out one (solid → liquid → gas), particles need more energy, so energy is taken in. Going the other way (gas → liquid → solid) gives energy out.
Watch out: in a change of state no new substance is made — it is still water, just in a different form. Energy still moves though!
An exothermic reaction gives out energy to the surroundings, usually as heat. Because energy leaves the reaction and warms everything around it, the temperature rises.
Remember: exo = exit — heat exits the reaction, so it feels hot and the thermometer reading goes up.
An endothermic reaction takes in energy from the surroundings. Because energy is pulled out of everything nearby, the temperature falls and the mixture feels cold.
Remember: endo = into — heat goes into the reaction, so it feels cold and the thermometer reading goes down.
The easiest way to tell the two apart is to measure the temperature before and after with a thermometer:
Misconception buster: "exothermic" does not mean "gets cold". It means heat exits the reaction, so the surroundings get warmer.
Tap a change, then tap the box it belongs in.
These energy changes are all around you. Here are ones you should be able to name:
Tip: most reactions you meet at KS3 (especially burning and neutralisation) are exothermic. Endothermic ones are rarer, which is why cold packs feel surprising!
Tap an example on the left, then its matching type on the right.
Atoms in molecules are joined by bonds. During a reaction the old bonds must be broken and new bonds are made. The key idea:
Whether a reaction is exo- or endothermic depends on the balance: if making the new bonds gives out more than breaking the old ones took in, energy is left over as heat — that's exothermic.
In an exothermic reaction it can look like energy is created — but it isn't. The energy was already stored in the chemical bonds. The reaction simply releases it to the surroundings.
In an endothermic reaction it can look like energy disappears — but it doesn't. It has been taken in and stored in the new bonds instead.
Misconception buster: energy is never made or destroyed. It only moves between the chemicals and their surroundings — this is conservation of energy.
It is exothermic. The hand-warmer gives out heat to the surroundings, which is why it feels hot and the temperature rises. Energy is being released from the chemicals inside it.
Exothermic: gives out heat → temperature rises (burning, neutralisation, hand-warmers).
Endothermic: takes in heat → temperature falls, feels cold (cold packs, thermal decomposition).
Changes of state: melting/boiling take energy in; freezing/condensing give energy out.
Bonds: breaking bonds takes energy in; making bonds gives energy out.
Conservation: energy is never made or destroyed — it only moves.
You've covered the whole of KS3 Energetics. Press Finish to see your score.
You've worked through Chemistry — Energetics for KS3 Science. 🎉
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Next: test yourself in the Evaluate stage Confidence Quiz, then lock it in with Verify.