Question: Why is fire hot?

David Pyle answered on 20 Mar 2011:

Fire – or combustion – is a process that releases a lot of energy. It usually involves the very rapid oxidation of a ‘fuel’ (e.g. a hydrocarbon – oil, methane gas) by oygen. At normal surface temperatures and pressures there aren’t many materials that will spontaneously combust (apart from things like sodium and potassium), but once the barrier to combustion has been overcome (e.g. by adding a spark), the process can then become self-sustaining as the heat from combustion allows further combustion to take place, until either the fuel or the oxidant have run out.