Question #dcfef

1 Answer
Jul 9, 2017

Well, the simple explanation is that combustion involves using #"O"_2#, oxygen gas, to burn... something. Could be a hydrocarbon, could be an alcohol, could be something else.

For example, if you burn methane completely, in open air:

#"CH"_4(g) + 2"O"_2(g) -> "CO"_2(g) + 2"H"_2"O"(g)#

And well, if you burn something, you're going to release heat into the atmosphere.

So, by definition, the reaction is exothermic, because it releases heat from the system (the reaction) out to the surroundings (the atmosphere).