A chemical reaction occurs when reactants react to form new substances, called the products. The Law of Conservation of Mass says that matter can be neither created nor destroyed.
Ice melting is an example of a physical change, whereas magnesium being eaten away by an acid is an example of a chemical change.
Some reactions produce heat. These aree called exothermic reactions. With an endothermic reaction, the mixture feels colder.
Rusting is an example of a corrosion reaction. To prevent iron being corroded, it is often coated with a layer of zinc. It is then called galvanised iron.
Combustion reactions are those where burning occurs. When a single chemical breaks down into 2 or more chemical, this is known as a decomposition reaction.
A water based solution is also known as an aqueous solution. Sometimes when 2 solutions are added, a solid appears. This reaction is called a precipitation reaction.