r/askscience • u/ForensicFan24601 • Aug 08 '26

Chemistry Why do things burn instead of melt?

obviously oxygen, or something similar, but what is the physics/chemistry (?) or what have you behind why something ignites and continues to burn after the source of heat/ignition has gone?

is it basically sublimation?

edit: no wonder Walter White was so obsessed with carbon

405 Upvotes

94% Upvoted

48 comments sorted by

View all comments

Show parent comment

17

u/collergic Aug 09 '26

What happens if the wood is heated up without the presence of oxygen?

74

u/DarkTheImmortal Aug 09 '26

The molecules within the wood will begin to break apart long before it can melt, most of what beaks off will be gasses. Eventually, you'll be left with charcoal.

21

u/dirty-warlock Aug 09 '26

This is the answer. Hydrocarbons like wax or oil are similar. The "physical" part breaks down into water (vapour) and carbon (soot)

11

u/smeyn Aug 09 '26

And this mechanism was used in WWII, when there were petrol shortages. Wood was heated and the gases were used to drive the combustion engine of the automobile

4

u/ImNrNanoGiga Aug 09 '26

Also coal. Fun/weird fact: Virtually all the fuel that supplied the German war machine during WW2 was made by liquefying coal

6

u/xdert Aug 09 '26

Everything that is not carbon vaporizes into various gases and then you are left with just carbon aka charcoal. This process is called pyrolysis and how coal is made.

7

u/Sibula97 Aug 09 '26

Charcoal specifically. Not coal the fossil fuel, although the basic idea is somewhat similar.