# Question #66793

Coal formed from immense tropical swamp-forests millions of years ago. Some of the plants when they died did not rot away completely leaving the carbon (from the $C {O}_{2}$ they absorbed when alive and converted to carbohydrates by photosynthesis) to be compressed in bands for geological times to form coal.
When we burn it the carbon again bonds with oxygen to release heat energy in the reaction $C + {O}_{2} \rightarrow C {O}_{2} + h e a t$