Energy stored in chemicals — Chemistry, 7–10 years
Some substances can release energy when they change, while others take in energy during a change. This explains why food can power a body and a battery can power a torch.
Chemicals can be energy stores
A substance is not only made of matter; it can also hold energy in the way its tiny parts are arranged. When the substance changes, some of that stored energy may come out as heat, light or movement. Food and fuels are familiar examples.
Why do changes warm things?
People needed to explain more than the new substances made in a change. They also noticed that some changes heat their surroundings, while others make things colder or need warming first. Thinking about energy helps us predict these effects instead of treating them as surprises.
A hand warmer
A hand warmer contains iron powder, water and air inside a pouch. Open it and oxygen from the air reaches the iron; the iron slowly changes and the pouch becomes warm. The warmth is energy released by that chemical change, not heat appearing from nowhere.
Energy is not a substance
It is easy to imagine energy as a liquid hidden inside food or a battery, waiting to pour out. That picture is useful for talking, but energy is not an extra material you can scoop out. It is a way of describing what can cause movement, heating, light or other changes.
Food, batteries and fuels
Your body changes food and uses some of the released energy for movement and warmth. A battery changes chemicals to push electric charge through a circuit. A fuel can release energy to move a car or heat a home, although burning it also makes waste gases.
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