An organic substance, as coal, petroleum etc. found
underground in deposits formed in previous geologic
period and used as a source of energy.
They are
formed from the remains of living organisms and all
have a high carbon or hydrogen content.
Their values
as fuel relies on the exothermic oxidation of carbon
to form carbon dioxide
(C + O2 _> CO2) and the
oxidation of hydrogen to form water
(H2 +
½O2
_> H2O)
