Foolestroupe is quite correct. In a chemical reaction, most times energy is either absorbed or released. The energy goes to make or to break a chemical bond and tends to be either heat or light depending on the reaction. If it takes a certain amount of energy to create bond, when the bond breaks an equivalent amount of energy is released.
Essentially no matter is created and no energy is created that wasn't already there. It is just moved around a bit.
A plant absorbs energy as light and uses it to convert water plus carbon dioxide from the air into woody tissue. When you put the log on a fire the log turns back to water vapour plus carbon dioxide, and the energy holding it all together is released as heat energy and ends up warming your room.
None of this has anything to do with a nuclear bomb converting mass to energy or Einstein's EE equals EMM SEE Squared, which, If I
recall is something to do with how mass being moved at the speed of light.
Quack!
GtD.