What Are Chemical Changes?

A chemical change is a change that creates one or more new substances with different properties from the original materials. When a chemical change happens, the atoms in the materials rearrange to form something completely new. Chemical changes are important because they explain many everyday events, from cooking food to the way our bodies digest meals.

The key difference between chemical and physical changes is what happens to the substance. In a physical change, a material might look different, but it is still the same substance. For example, when water freezes into ice, it changes form but remains water. You can easily reverse this change by melting the ice. However, in a chemical change, the original substance is gone forever. You cannot easily reverse a chemical change because new substances with different properties (characteristics like color, texture, and smell) have formed.

Burning wood is a perfect example of a chemical change. When wood burns, it combines with oxygen in the air and creates ash, smoke, and gases. The ash and smoke have completely different properties from wood. Ash is gray powder that crumbles easily, while wood is brown and solid. You cannot turn ash and smoke back into wood. This is like mixing ingredients to bake a cake—once the cake is baked, you cannot separate it back into eggs, flour, and sugar.

Another common chemical change is rusting. When iron or steel gets wet and is exposed to oxygen, it forms rust. Rust is a reddish-brown substance that flakes off easily. It has different properties from shiny, strong iron. The iron has chemically changed into a new substance called iron oxide. Rusting is a slow chemical change that can take days or weeks.

Scientists look for clues to identify chemical changes. These clues include color changes, the production of gas (bubbles), the release of heat or light, and the formation of a solid from two liquids. For example, when baking soda mixes with vinegar, it produces bubbles of carbon dioxide gas. This is evidence that a chemical reaction (another name for a chemical change) has occurred.

Interesting Fact: When you digest food, your body uses chemical changes to break down what you eat into nutrients your cells can use. Without chemical changes, you could not get energy from food!