When fossil are burned, their chemical potential energy is converted into?

Fossil fuel is a source of non-renewable energy. There are many examples of fossil fuels which we use in our daily lives. In fact, most of the energy that we consume is fossil fuels. Coal, petroleum, natural gas, these are all considered as fossil fuels. Many years ago, to be specific, during the carboniferous age, due to the change in atmospheric condition and other changes, there forests were destroyed and they were fossilized. With the action of bacteria and other microorganisms in the surface of the earth, these trees and other vegetation were decayed and disintegrated. Years after these trees were available in solid, liquid and gaseous state. The solid form is coal. It is the most widely used form of fossil fuel in domestic purposes.