Chemical reaction

A chemical reaction happens when one or more chemicals are changed into one or more other chemicals. Examples:

• iron and oxygen combining to make rust
• vinegar and baking soda combining to make sodium acetate, carbon dioxide and water
• things burning or exploding
• many reactions that happen inside living things, such as photosynthesis
• electrochemical reactions when discharging or recharging batteries

Some reactions are fast, and others are slow. Some happen at different speeds, depending on temperature or other things. For example, wood does not react with air when it is cold, but if it is made hot enough, it will start to burn. Some reactions give out energy. These are exothermic reactions. In other reactions, energy is taken in. These are endothermic reactions.

Nuclear reactions are not chemical reactions. Chemical reactions involve only the electrons of atoms; nuclear reactions involve the protons and neutrons in the atomic nuclei.