Chemistry/Content/Chemical Reactions

Water boils to become vapor. Only the form changes i.e. liquid becomes gas, but the chemical nature of water -- the water molecule -- remains the same. This is an example of physical reaction. A piece of coal burns up on igniting. The carbon in the coal combines with oxygen in the air to become Carbon Dioxide (CO2). CO2 is a completely different chemical with properties different from carbon or oxygen. This is an example of a chemical reaction.