Why Paper Burns

This week's experiment is a result of a question sent to me by a list member. It is one of those questions that seems so simple until you try to explain it. To get started, you will need:

- a strip of paper about 4 inches long
- a pan of water
- a match or lighter

Warning: This experiment uses fire. Never work with fire unless there is an adult with you. That gives you someone to blame if something goes wrong.

Hold the paper over the water. Use the match to light the end of the paper. Watch it burn for a second, noticing the light and heat coming from the flame. Then drop it into the water to put it out. Why does the paper produce that light and heat? Why does it burn?

The key to the answer is energy. There are many kinds of energy, such as heat, light, electrical, nuclear (pronounced nu-cle-ar, not nuk-u-ler), etc. The laws of thermodynamics tell us that we cannot make energy, and we cannot get rid of it. We can only change it from one form to another.

The light and heat energy of the burning paper had to come from somewhere. It came from the paper. Now, where did the paper come from? Paper is made from wood. And where does wood come from? Trees.

Trees are plants. Where do plants get their energy? From the sun. Plants use a process called photosynthesis to trap energy from the sun. They combine water, carbon (The black stuff left behind when you burned the paper.) and the energy from sunlight to make sugar.

This sugar is then used to make other chemicals. By connecting many sugar molecules together into a long chain, the plant produces cellulose. That is what wood is made of. A piece of wood is really just a big chunk of sugar. The chemical structure has been changed, so it does not taste sweet, but it still contains the energy that was put into the sugar. When you burn a piece of wood, the heat causes the molecules to come apart, releasing the trapped energy, as the light and heat of the flame.

If you take the piece of wood and mash it into a pulp, then you can process it into a sheet of paper. Although it looks different, it is still made of cellulose, so it still contains the trapped energy. Burning the paper releases the energy, just as it does when you burn a piece of wood.

Now, look at another piece of paper. You can't see the energy, but it is there, hidden inside. Science is hidden all around you, if you just take the time to wonder about things.