Chemical Changes in Matter

What are chemical changes?

In the previous lesson we looked at physical changes in matter. Chemical changes can also happen in matter. A chemical change involves a reaction which causes matter to change into a new substance. Look at the examples below:

• When we burn a piece of paper, we end up with ash. Ash is a very different substance from the paper we started with.

• If we leave a nail on the ground outside, it will rust. The metal will change into a substance which is different from the metal the nail was made out of.

• If we cook an egg, it will turn into a different substance. A cooked egg is very different from a raw egg.

• If a ripe mango is left on the ground outside for a long time, it will rot. A rotten mango is very different from a ripe mango. It looks and smells different. It probably tastes different too but let’s not try to find out.

The changes above are all chemical changes, because they cause matter to change into a different substance. Often, chemical changes cannot be reversed. For instance, you cannot turn a cooked egg back into a raw egg. Also, you cannot turn the ash back into paper.

You can observe some chemical changes

Chemical reactions can sometimes be observed. A rusty nail looks and feels different from one that is not rusty. When a piece of paper burns, heat and light are produced. You can also smell the paper burning.