A chemical reaction involves change. For example, two substances coming together to form a new substance is a chemical reaction. So, when you mix baking soda and vinegar together, you are causing a chemical reaction. In this reaction, a portion of the baking soda and vinegar is changed into carbon dioxide gas, which produces the bubbles you see!

A chemical is any substance that is involved in a chemical reaction. The reactants that cause the reaction (the baking soda and the vinegar) or a product of the reaction (the gas bubbles that form) are all chemicals. Based on this definition, almost anything can be considered a chemical, since almost anything can be made to undergo a chemical change given the right conditions (such as high temperature).

Some chemicals, though, are more valuable than others. For example, petrochemicals are a type of chemicals obtained from oil (also called petroleum) or natural gas. To produce petrochemicals, oil companies first drill into the ground to access reservoirs of crude oil (called crude because it is unrefined and consists of a mixture of natural chemicals). This crude oil is then sent to an oil refinery, where it is separated into different chemicals. Some of these chemicals include gasoline and diesel used in cars and trucks, and some are converted into petrochemicals. These petrochemicals include plastics, food additives, and even medicine!