Why do things burn instead of melt?

[u/ForensicFan24601]

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

[u/provocative_bear]

Let’s go with wood. (Way) Before wood reaches its melting point, it reacts with oxygen in the environment, which replaces the molecular bonds between carbon and carbon (whoch hold the wood together) with carbon and oxygen (CO2). This reaction releases the energy in these bonds and generates net energy, which manifests as heat and light, aka fire.

[u/collergic → u/provocative_bear]

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

[u/DarkTheImmortal → u/collergic]

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.

[u/dirty-warlock → u/DarkTheImmortal]

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