Many energy sources commonly used by humans are forms of chemical energy. They are usually labeled "fuels." The way to use the chemical energy in most fuels is by burning them, as we do with wood, natural gas, gasoline, coal, and others. When these fuels burn, they give off heat, because the chemical reaction called combustion is an exothermic reaction. That is, the reaction releases thermal energy in the form of heat.
Some chemicals contain a great deal of energy that can be released all at once. These chemicals are called explosives. For example, when dynamite explodes, its chemical energy changes very quickly into thermal and radiant energy and transfers from a potential state to a kinetic state.